[moderation] [exfat?] KCSAN: data-race in _copy_to_iter / fat32_ent_put (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ea1013c15392 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16a8d31a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=8439c7e7cbd735b50c95
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/e71363ad5fa5/disk-ea1013c1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7d02687e9370/vmlinux-ea1013c1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1289ed40062b/bzImage-ea1013c1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8439c7...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _copy_to_iter / fat32_ent_put

read-write to 0xffff88811ce8e008 of 4 bytes by task 3818 on cpu 0:
fat32_ent_put+0x4e/0x90 fs/fat/fatent.c:191
fat_ent_write+0x6c/0xe0 fs/fat/fatent.c:417
fat_chain_add+0x15d/0x440 fs/fat/misc.c:136
fat_add_entries+0xcc9/0xfc0 fs/fat/dir.c:1393
vfat_add_entry+0x19a2/0x1b90 fs/fat/namei_vfat.c:674
vfat_create+0xa8/0x190 fs/fat/namei_vfat.c:768
lookup_open fs/namei.c:4440 [inline]
open_last_lookups fs/namei.c:4540 [inline]
path_openat+0x1115/0x23b0 fs/namei.c:4784
do_filp_open+0x109/0x230 fs/namei.c:4814
do_sys_openat2+0xa6/0x150 fs/open.c:1430
do_sys_open fs/open.c:1436 [inline]
__do_sys_creat fs/open.c:1514 [inline]
__se_sys_creat fs/open.c:1508 [inline]
__x64_sys_creat+0x65/0x90 fs/open.c:1508
x64_sys_call+0x2f1c/0x3000 arch/x86/include/generated/asm/syscalls_64.h:86
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811ce8e000 of 512 bytes by task 3309 on cpu 1:
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:197
copy_page_to_iter+0x18f/0x2d0 lib/iov_iter.c:374
copy_folio_to_iter include/linux/uio.h:204 [inline]
filemap_read+0x407/0xa00 mm/filemap.c:2851
blkdev_read_iter+0x22d/0x2e0 block/fops.c:856
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+0x2889/0x3000 arch/x86/include/generated/asm/syscalls_64.h:1
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3309 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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