[moderation] [fs?] KCSAN: data-race in setattr_copy / vfs_write (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e5f0a698b34e Linux 6.17
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=155bfae2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c7f65ba98bb01573
dashboard link: https://syzkaller.appspot.com/bug?extid=4fde77d66555ad4c1ef9
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [bra...@kernel.org ja...@suse.cz 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/ba163e979014/disk-e5f0a698.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bdc84f9d05a1/vmlinux-e5f0a698.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3a8e9862c64c/bzImage-e5f0a698.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4fde77...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in setattr_copy / vfs_write

write to 0xffff888119ca4f08 of 2 bytes by task 7703 on cpu 1:
setattr_copy+0x199/0x4b0 fs/attr.c:352
shmem_setattr+0x566/0x840 mm/shmem.c:1375
notify_change+0x809/0x890 fs/attr.c:552
chmod_common+0x138/0x270 fs/open.c:650
do_fchmodat+0xcd/0x180 fs/open.c:697
__do_sys_chmod fs/open.c:721 [inline]
__se_sys_chmod fs/open.c:719 [inline]
__x64_sys_chmod+0x38/0x50 fs/open.c:719
x64_sys_call+0x291c/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:91
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888119ca4f08 of 2 bytes by task 7698 on cpu 0:
file_end_write include/linux/fs.h:3126 [inline]
vfs_write+0x757/0x960 fs/read_write.c:694
ksys_write+0xda/0x1a0 fs/read_write.c:738
__do_sys_write fs/read_write.c:749 [inline]
__se_sys_write fs/read_write.c:746 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:746
x64_sys_call+0x27fe/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x8000 -> 0x8120

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 7698 Comm: syz.3.956 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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