[syzbot] [wireless?] BUG: using smp_processor_id() in preemptible code in ieee80211_tx_control_port

[syzbot] [wireless?] BUG: using smp_processor_id() in preemptible code in ieee80211_tx_control_port

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    a9d7ced84989 Add linux-next specific files for 20260908
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=149cfaf9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=17eeb09695a2b3c9
dashboard link: https://syzkaller.appspot.com/bug?extid=d979bd35c8a76fd1b6f5
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=129cfaf9580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=139866f9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4f470407358e/disk-a9d7ced8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/858b9d7ba687/vmlinux-a9d7ced8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ef971d22d75f/bzImage-a9d7ced8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d979bd35c8a76fd1b6f5@syzkaller.appspotmail.com

BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor240/5639
caller is dev_sw_netstats_tx_add include/linux/netdevice.h:3086 [inline]
caller is ieee80211_tx_control_port+0xac7/0x1100 net/mac80211/tx.c:6656
CPU: 0 UID: 0 PID: 5639 Comm: syz-executor240 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 check_preemption_disabled+0xcd/0xd0 lib/smp_processor_id.c:47
 dev_sw_netstats_tx_add include/linux/netdevice.h:3086 [inline]
 ieee80211_tx_control_port+0xac7/0x1100 net/mac80211/tx.c:6656
 rdev_tx_control_port net/wireless/rdev-ops.h:783 [inline]
 nl80211_tx_control_port+0x624/0x960 net/wireless/nl80211.c:18603
 genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114
 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
 genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x7c3/0xae0 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800
 __sock_sendmsg net/socket.c:815 [inline]
 ____sys_sendmsg+0x54e/0x850 net/socket.c:2713
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2767
 __sys_sendmsg net/socket.c:2799 [inline]
 __do_sys_sendmsg net/socket.c:2804 [inline]
 __se_sys_sendmsg net/socket.c:2802 [inline]
 __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2802
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2fe280ba69
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 d0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc9ac26a08 EFLAGS: 00000246 ORIG_RAX: 000000000000002e



---
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Forwarded: [PATCH] mac80211: fix using smp_processor_id() in preemptible code in ieee80211_tx_control_port()

[syzbot]

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***

Subject: [PATCH] mac80211: fix using smp_processor_id() in preemptible code in ieee80211_tx_control_port()
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master


ieee80211_tx_control_port() can be called from nl80211_tx_control_port()
in normal process context via netlink sendmsg(), where BH/preemption
is not disabled. dev_sw_netstats_tx_add() uses this_cpu_ptr() internally,
which requires preemption to be disabled, triggering a
"BUG: using smp_processor_id() in preemptible code" warning.

Fix this by moving the local_bh_disable()/local_bh_enable() section to
also cover dev_sw_netstats_tx_add() and ieee80211_tpt_led_trig_tx().

Reported-by: syzbot+d979bd35c8a76fd1b6f5@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d979bd35c8a76fd1b6f5
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 net/mac80211/tx.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 74ab27534076..7b1a3c63e5dc 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -6687,10 +6687,9 @@ int ieee80211_tx_control_port(struct wiphy *wiphy, struct net_device *dev,
 		return -EINVAL;
 	}
 
+	local_bh_disable();
 	dev_sw_netstats_tx_add(dev, 1, skb->len);
 	ieee80211_tpt_led_trig_tx(local, skb->len);
-
-	local_bh_disable();
 	ieee80211_xmit(sdata, sta, skb);
 	local_bh_enable();
 	rcu_read_unlock();
-- 
2.34.1