[moderation] [exfat?] KCSAN: data-race in fat_alloc_clusters / fat_statfs (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e04c78d86a96 Linux 6.16-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14561e82580000
kernel config: https://syzkaller.appspot.com/x/.config?x=25d7df3a6a1d1ea6
dashboard link: https://syzkaller.appspot.com/bug?extid=84a49682e970f5bd639f
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
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/f87b79b04409/disk-e04c78d8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/088c606067af/vmlinux-e04c78d8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a09832cb8794/bzImage-e04c78d8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+84a496...@syzkaller.appspotmail.com

SELinux: security_context_str_to_sid (root) failed with errno=-22
==================================================================
BUG: KCSAN: data-race in fat_alloc_clusters / fat_statfs

write to 0xffff888118c5c0ac of 4 bytes by task 7533 on cpu 1:
fat_alloc_clusters+0x662/0xa80 fs/fat/fatent.c:511
fat_add_cluster fs/fat/inode.c:107 [inline]
__fat_get_block fs/fat/inode.c:154 [inline]
fat_get_block+0x258/0x5e0 fs/fat/inode.c:189
__block_write_begin_int+0x400/0xf90 fs/buffer.c:2151
block_write_begin fs/buffer.c:2262 [inline]
cont_write_begin+0x5fc/0x970 fs/buffer.c:2601
fat_write_begin+0x4f/0xe0 fs/fat/inode.c:228
generic_perform_write+0x184/0x490 mm/filemap.c:4112
__generic_file_write_iter+0x9e/0x120 mm/filemap.c:4229
generic_file_write_iter+0x8d/0x2f0 mm/filemap.c:4255
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x4a0/0x8e0 fs/read_write.c:686
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+0x2cdd/0x2fb0 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

read to 0xffff888118c5c0ac of 4 bytes by task 7544 on cpu 0:
fat_statfs+0x182/0x200 fs/fat/inode.c:843
statfs_by_dentry fs/statfs.c:66 [inline]
vfs_statfs+0xc8/0x1c0 fs/statfs.c:90
user_statfs+0x71/0x110 fs/statfs.c:105
__do_sys_statfs fs/statfs.c:193 [inline]
__se_sys_statfs fs/statfs.c:190 [inline]
__x64_sys_statfs+0x65/0xf0 fs/statfs.c:190
x64_sys_call+0x1edd/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:138
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: 0x00001f52 -> 0x00001f51

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 7544 Comm: syz.6.1473 Not tainted 6.16.0-rc2-syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.