[moderation] [fs?] KCSAN: data-race in ____sys_sendmsg / fasync_insert_entry (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ad8d485e6658 Merge tag 'vfs-7.2-rc8.fixes' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12a6d279580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e71a508528491732
dashboard link: https://syzkaller.appspot.com/bug?extid=d56390baaf94bccb2fc6
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
CC: [alex....@gmail.com bra...@kernel.org c...@kernel.org ja...@suse.cz jla...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/77cbe89999b0/disk-ad8d485e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3bbad2d26832/vmlinux-ad8d485e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/71d04b52a37a/bzImage-ad8d485e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d56390...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in ____sys_sendmsg / fasync_insert_entry

read-write to 0xffff88810f3a6da8 of 4 bytes by task 27752 on cpu 1:
fasync_insert_entry+0x120/0x150 fs/fcntl.c:1071
fasync_add_entry fs/fcntl.c:1098 [inline]
fasync_helper+0x5e/0xc0 fs/fcntl.c:1116
sock_fasync+0x58/0xc0 net/socket.c:1526
setfl fs/fcntl.c:76 [inline]
do_fcntl+0xd5e/0xf80 fs/fcntl.c:477
__do_sys_fcntl fs/fcntl.c:602 [inline]
__se_sys_fcntl+0xb1/0x120 fs/fcntl.c:587
__x64_sys_fcntl+0x43/0x50 fs/fcntl.c:587
x64_sys_call+0x2844/0x3020 arch/x86/include/generated/asm/syscalls_64.h:73
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810f3a6da8 of 4 bytes by task 27744 on cpu 0:
____sys_sendmsg+0x247/0x580 net/socket.c:2669
___sys_sendmsg+0x195/0x1e0 net/socket.c:2738
__sys_sendmmsg+0x185/0x320 net/socket.c:2827
__do_sys_sendmmsg net/socket.c:2854 [inline]
__se_sys_sendmmsg net/socket.c:2851 [inline]
__x64_sys_sendmmsg+0x57/0x70 net/socket.c:2851
x64_sys_call+0x27aa/0x3020 arch/x86/include/generated/asm/syscalls_64.h:308
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000002 -> 0x00042002

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 27744 Comm: syz.7.7588 Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
==================================================================


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