[moderation] [fs?] KCSAN: data-race in inode_permission / setattr_copy

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cbf33b8e0b36 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1283f6e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=eef77ae4d2c90cf6
dashboard link: https://syzkaller.appspot.com/bug?extid=8c336f4872e0262487f5
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/5670ae8b43dd/disk-cbf33b8e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0bd533499004/vmlinux-cbf33b8e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0bb2d9373440/bzImage-cbf33b8e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8c336f...@syzkaller.appspotmail.com

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

write to 0xffff88811e136f00 of 2 bytes by task 12647 on cpu 0:
setattr_copy+0x199/0x4b0 fs/attr.c:352
shmem_setattr+0x566/0x840 mm/shmem.c:1338
notify_change+0x806/0x890 fs/attr.c:552
chmod_common+0x138/0x270 fs/open.c:650
do_fchmodat+0xcd/0x180 fs/open.c:697
__do_sys_fchmodat fs/open.c:716 [inline]
__se_sys_fchmodat fs/open.c:713 [inline]
__x64_sys_fchmodat+0x42/0x50 fs/open.c:713
x64_sys_call+0x2891/0x3000 arch/x86/include/generated/asm/syscalls_64.h:269
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 0xffff88811e136f00 of 2 bytes by task 12646 on cpu 1:
devcgroup_inode_permission include/linux/device_cgroup.h:21 [inline]
inode_permission+0x8d/0x310 fs/namei.c:597
may_lookup fs/namei.c:1858 [inline]
link_path_walk+0x162/0x900 fs/namei.c:2467
path_lookupat+0x63/0x2a0 fs/namei.c:2675
filename_lookup+0x147/0x340 fs/namei.c:2705
user_path_at+0x3e/0x130 fs/namei.c:3215
do_fchmodat+0x9c/0x180 fs/open.c:695
__do_sys_fchmodat fs/open.c:716 [inline]
__se_sys_fchmodat fs/open.c:713 [inline]
__x64_sys_fchmodat+0x42/0x50 fs/open.c:713
x64_sys_call+0x2891/0x3000 arch/x86/include/generated/asm/syscalls_64.h:269
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: 0x41c0 -> 0x4ffb

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 12646 Comm: syz.6.3065 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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