[moderation] [exfat?] KCSAN: data-race in _copy_to_iter / fat16_ent_put (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 55027e689933 Merge tag 'input-for-v6.10-rc5' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=109bf03a980000
kernel config: https://syzkaller.appspot.com/x/.config?x=7e87b541dc1fc960
dashboard link: https://syzkaller.appspot.com/bug?extid=97168ef73dca8775edb2
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
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/12deab70203e/disk-55027e68.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/29d492adc137/vmlinux-55027e68.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f5d493b5e976/bzImage-55027e68.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+97168e...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _copy_to_iter / fat16_ent_put

write to 0xffff88813d92115c of 2 bytes by task 3380 on cpu 0:
fat16_ent_put+0x28/0x60 fs/fat/fatent.c:183
fat_alloc_clusters+0x4c9/0xa80 fs/fat/fatent.c:503
fat_add_cluster fs/fat/inode.c:108 [inline]
__fat_get_block fs/fat/inode.c:155 [inline]
fat_get_block+0x25c/0x5e0 fs/fat/inode.c:190
__block_write_begin_int+0x417/0xfa0 fs/buffer.c:2128
__block_write_begin fs/buffer.c:2177 [inline]
block_write_begin+0x7b/0x170 fs/buffer.c:2236
cont_write_begin+0x486/0x6b0 fs/buffer.c:2590
fat_write_begin+0x61/0xf0 fs/fat/inode.c:230
generic_perform_write+0x1d5/0x410 mm/filemap.c:4015
__generic_file_write_iter+0xec/0x120 mm/filemap.c:4107
generic_file_write_iter+0x7d/0x1d0 mm/filemap.c:4136
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0x78f/0x900 fs/read_write.c:590
ksys_write+0xeb/0x1b0 fs/read_write.c:643
__do_sys_write fs/read_write.c:655 [inline]
__se_sys_write fs/read_write.c:652 [inline]
__x64_sys_write+0x42/0x50 fs/read_write.c:652
x64_sys_call+0x27ef/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88813d921000 of 512 bytes by task 3386 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:29 [inline]
iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
iterate_and_advance include/linux/iov_iter.h:271 [inline]
_copy_to_iter+0x126/0xaf0 lib/iov_iter.c:185
copy_page_to_iter+0x171/0x2b0 lib/iov_iter.c:362
copy_folio_to_iter include/linux/uio.h:180 [inline]
filemap_read+0x42c/0x690 mm/filemap.c:2676
blkdev_read_iter+0x217/0x2c0 block/fops.c:749
new_sync_read fs/read_write.c:395 [inline]
vfs_read+0x5e6/0x6e0 fs/read_write.c:476
ksys_read+0xeb/0x1b0 fs/read_write.c:619
__do_sys_read fs/read_write.c:629 [inline]
__se_sys_read fs/read_write.c:627 [inline]
__x64_sys_read+0x42/0x50 fs/read_write.c:627
x64_sys_call+0x27e5/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:1
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3386 Comm: udevd Not tainted 6.10.0-rc5-syzkaller-00018-g55027e689933 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup