[PATCH v2] netlabel: Fix NULL pointer exception caused by CALIPSO on IPv4 sockets

[Debin Zhu <mowenroot@163.com>]

Vulnerability Description:

	From Linux Kernel v4.0 to the latest version, 
	a type confusion issue exists in the `netlbl_conn_setattr` 
	function (`net/netlabel/netlabel_kapi.c`) within SELinux, 
	which can lead to a local DoS attack.

	When calling `netlbl_conn_setattr`, 
	`addr->sa_family` is used to determine the function behavior. 
	If `sk` is an IPv4 socket, 
	but the `connect` function is called with an IPv6 address, 
	the function `calipso_sock_setattr()` is triggered. 
	Inside this function, the following code is executed:

	sk_fullsock(__sk) ? inet_sk(__sk)->pinet6 : NULL;

	Since `sk` is an IPv4 socket, `pinet6` is `NULL`, 
	leading to a null pointer dereference and triggering a DoS attack.

<TASK>
calipso_sock_setattr+0x4f/0x80 net/netlabel/netlabel_calipso.c:557
netlbl_conn_setattr+0x12a/0x390 net/netlabel/netlabel_kapi.c:1152
selinux_netlbl_socket_connect_helper 
selinux_netlbl_socket_connect_locked+0xf5/0x1d0 
selinux_netlbl_socket_connect+0x22/0x40 security/selinux/netlabel.c:611
selinux_socket_connect+0x60/0x80 security/selinux/hooks.c:4923
security_socket_connect+0x71/0xb0 security/security.c:2260
__sys_connect_file+0xa4/0x190 net/socket.c:2007
__sys_connect+0x145/0x170 net/socket.c:2028
__do_sys_connect net/socket.c:2038 [inline]
__se_sys_connect net/socket.c:2035 [inline]
__x64_sys_connect+0x6e/0xb0 net/socket.c:2035
do_syscall_x64 arch/x86/entry/common.c:51 

Affected Versions:

- Linux 4.0 - Latest Linux Kernel version

Reproduction Steps:

	Use the `netlabelctl` tool and 
	run the following commands to trigger the vulnerability:

	netlabelctl map del default
	netlabelctl cipsov4 add pass doi:8 tags:1
	netlabelctl map add default address:192.168.1.0/24 protocol:cipsov4,8
	netlabelctl calipso add pass doi:7
	netlabelctl map add default address:2001:db8::1/32 protocol:calipso,7

Then, execute the following PoC code:

	int sockfd = socket(AF_INET, SOCK_STREAM, 0);

	struct sockaddr_in6 server_addr = {0};
	server_addr.sin6_family = AF_INET6;     
	server_addr.sin6_port = htons(8080);    

	const char *ipv6_str = "2001:db8::1";    
	inet_pton(AF_INET6, ipv6_str, &server_addr.sin6_addr);

	connect(sockfd, (struct sockaddr*)&server_addr, sizeof(server_addr));

Suggested Fix:

	When using an IPv4 address on an IPv6 UDP/datagram socket, 
	the operation will invoke the IPv4 datagram code through 
	the IPv6 datagram code and execute successfully. 
	It is necessary to check whether the `pinet6` pointer 
	returned by `inet6_sk()` is NULL; otherwise, 
	unexpected issues may occur.

Signed-off-by: Debin Zhu <mowenroot@163.com>
Signed-off-by: Bitao Ouyang <1985755126@qq.com>
---
 net/ipv6/calipso.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/calipso.c b/net/ipv6/calipso.c
index dbcea9fee..a8a8736df 100644
--- a/net/ipv6/calipso.c
+++ b/net/ipv6/calipso.c
@@ -1072,8 +1072,13 @@ static int calipso_sock_getattr(struct sock *sk,
 	struct ipv6_opt_hdr *hop;
 	int opt_len, len, ret_val = -ENOMSG, offset;
 	unsigned char *opt;
-	struct ipv6_txoptions *txopts = txopt_get(inet6_sk(sk));
+	struct ipv6_pinfo *pinfo = inet6_sk(sk);
+	struct ipv6_txoptions *txopts;
 
+	if (!pinfo)
+		return -EAFNOSUPPORT;
+
+	txopts = txopt_get(pinfo);
 	if (!txopts || !txopts->hopopt)
 		goto done;
 
@@ -1125,8 +1130,13 @@ static int calipso_sock_setattr(struct sock *sk,
 {
 	int ret_val;
 	struct ipv6_opt_hdr *old, *new;
-	struct ipv6_txoptions *txopts = txopt_get(inet6_sk(sk));
-
+	struct ipv6_pinfo *pinfo = inet6_sk(sk);
+	struct ipv6_txoptions *txopts;
+
+	if (!pinfo)
+		return -EAFNOSUPPORT;
+
+	txopts = txopt_get(pinfo);
 	old = NULL;
 	if (txopts)
 		old = txopts->hopopt;
@@ -1153,8 +1163,13 @@ static int calipso_sock_setattr(struct sock *sk,
 static void calipso_sock_delattr(struct sock *sk)
 {
 	struct ipv6_opt_hdr *new_hop;
-	struct ipv6_txoptions *txopts = txopt_get(inet6_sk(sk));
+	struct ipv6_pinfo *pinfo = inet6_sk(sk);
+	struct ipv6_txoptions *txopts;
 
+	if (!pinfo)
+		return;
+
+	txopts = txopt_get(pinfo);
 	if (!txopts || !txopts->hopopt)
 		goto done;
 
-- 
mowenroot@163.com