[moderation] [exfat?] KCSAN: data-race in _copy_to_iter / fat_set_state (13)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 24172e0d7990 Merge tag 'arm64-fixes' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12d170b4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d2e0bc0ae94545f7
dashboard link: https://syzkaller.appspot.com/bug?extid=d94ad363411061f84041
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [hiro...@mail.parknet.co.jp linki...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org sj155...@samsung.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/80c7c3f4b8d5/disk-24172e0d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/197bc87f09a8/vmlinux-24172e0d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8f10152201cb/bzImage-24172e0d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d94ad3...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _copy_to_iter / fat_set_state

write to 0xffff888123cfd025 of 1 bytes by task 8612 on cpu 1:
fat_set_state+0x16c/0x1e0 fs/fat/inode.c:-1
fat_fill_super+0x1875/0x1ce0 fs/fat/inode.c:1834
vfat_fill_super+0x24/0x30 fs/fat/namei_vfat.c:1197
get_tree_bdev_flags+0x291/0x300 fs/super.c:1691
get_tree_bdev+0x1f/0x30 fs/super.c:1714
vfat_get_tree+0x1c/0x30 fs/fat/namei_vfat.c:1202
vfs_get_tree+0x57/0x1d0 fs/super.c:1751
fc_mount fs/namespace.c:1208 [inline]
do_new_mount_fc fs/namespace.c:3651 [inline]
do_new_mount+0x24d/0x660 fs/namespace.c:3727
path_mount+0x4a5/0xb70 fs/namespace.c:4037
do_mount fs/namespace.c:4050 [inline]
__do_sys_mount fs/namespace.c:4238 [inline]
__se_sys_mount+0x28c/0x2e0 fs/namespace.c:4215
__x64_sys_mount+0x67/0x80 fs/namespace.c:4215
x64_sys_call+0x2b51/0x3000 arch/x86/include/generated/asm/syscalls_64.h:166
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 0xffff888123cfd000 of 512 bytes by task 3533 on cpu 0:
instrument_copy_to_user include/linux/instrumented.h:113 [inline]
copy_to_user_iter lib/iov_iter.c:24 [inline]
iterate_ubuf include/linux/iov_iter.h:30 [inline]
iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
iterate_and_advance include/linux/iov_iter.h:330 [inline]
_copy_to_iter+0x130/0xe70 lib/iov_iter.c:185
copy_page_to_iter+0x18f/0x2d0 lib/iov_iter.c:362
copy_folio_to_iter include/linux/uio.h:204 [inline]
filemap_read+0x407/0xa00 mm/filemap.c:2799
blkdev_read_iter+0x22d/0x2e0 block/fops.c:859
new_sync_read fs/read_write.c:491 [inline]
vfs_read+0x64c/0x770 fs/read_write.c:572
ksys_read+0xda/0x1a0 fs/read_write.c:715
__do_sys_read fs/read_write.c:724 [inline]
__se_sys_read fs/read_write.c:722 [inline]
__x64_sys_read+0x40/0x50 fs/read_write.c:722
x64_sys_call+0x27c0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:1
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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3533 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


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