[moderation] [exfat?] KCSAN: data-race in fat16_ent_get / fat16_ent_put (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b8f52214c61a Merge tag 'audit-pr-20241205' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=103bede8580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ff022027cd3a0001
dashboard link: https://syzkaller.appspot.com/bug?extid=ecf5a95b754e6caaf8d6
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/171a1524260d/disk-b8f52214.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1459062ef0b3/vmlinux-b8f52214.xz
kernel image: https://storage.googleapis.com/syzbot-assets/45e0e950d378/bzImage-b8f52214.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ecf5a9...@syzkaller.appspotmail.com

RBP: 0000000020000180 R08: 00007f66e0de4f10 R09: 0000000001a4243c
R10: 0000000001a4243c R11: 0000000000000246 R12: 0000000020000100
R13: 00007f66e0de4ed0 R14: 0000000000000000 R15: 0000000020000200
</TASK>
==================================================================
BUG: KCSAN: data-race in fat16_ent_get / fat16_ent_put

read to 0xffff88811b53a6d8 of 2 bytes by task 7893 on cpu 0:
fat16_ent_get+0x23/0x70 fs/fat/fatent.c:140
fat_ent_read+0x3e0/0x5a0 fs/fat/fatent.c:372
fat_chain_add+0x12d/0x400 fs/fat/misc.c:133
fat_add_cluster fs/fat/inode.c:112 [inline]
__fat_get_block fs/fat/inode.c:154 [inline]
fat_get_block+0x46b/0x5e0 fs/fat/inode.c:189
__block_write_begin_int+0x417/0xfa0 fs/buffer.c:2116
block_write_begin fs/buffer.c:2226 [inline]
cont_write_begin+0x546/0x860 fs/buffer.c:2577
fat_write_begin+0x51/0xe0 fs/fat/inode.c:228
cont_expand_zero fs/buffer.c:2504 [inline]
cont_write_begin+0x18b/0x860 fs/buffer.c:2567
fat_write_begin+0x51/0xe0 fs/fat/inode.c:228
generic_cont_expand_simple+0xaa/0x150 fs/buffer.c:2468
fat_cont_expand+0x3a/0x160 fs/fat/file.c:223
fat_setattr+0x2aa/0x840 fs/fat/file.c:513
notify_change+0x85c/0x8e0 fs/attr.c:552
do_truncate fs/open.c:65 [inline]
do_ftruncate+0x3cf/0x460 fs/open.c:181
do_sys_ftruncate fs/open.c:196 [inline]
__do_sys_ftruncate fs/open.c:201 [inline]
__se_sys_ftruncate fs/open.c:199 [inline]
__x64_sys_ftruncate+0x67/0xc0 fs/open.c:199
x64_sys_call+0x9d9/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:78
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

write to 0xffff88811b53a6d8 of 2 bytes by task 7897 on cpu 1:
fat16_ent_put+0x28/0x60 fs/fat/fatent.c:183
fat_ent_write+0x66/0xe0 fs/fat/fatent.c:417
fat_chain_add+0x15f/0x400 fs/fat/misc.c:136
fat_add_cluster fs/fat/inode.c:112 [inline]
__fat_get_block fs/fat/inode.c:154 [inline]
fat_get_block+0x46b/0x5e0 fs/fat/inode.c:189
__block_write_begin_int+0x417/0xfa0 fs/buffer.c:2116
block_write_begin fs/buffer.c:2226 [inline]
cont_write_begin+0x546/0x860 fs/buffer.c:2577
fat_write_begin+0x51/0xe0 fs/fat/inode.c:228
cont_expand_zero fs/buffer.c:2504 [inline]
cont_write_begin+0x18b/0x860 fs/buffer.c:2567
fat_write_begin+0x51/0xe0 fs/fat/inode.c:228
generic_cont_expand_simple+0xaa/0x150 fs/buffer.c:2468
fat_cont_expand+0x3a/0x160 fs/fat/file.c:223
fat_setattr+0x2aa/0x840 fs/fat/file.c:513
notify_change+0x85c/0x8e0 fs/attr.c:552
do_truncate+0x116/0x160 fs/open.c:65
vfs_truncate+0x1e9/0x240 fs/open.c:111
do_sys_truncate+0x95/0x130 fs/open.c:134
__do_sys_truncate fs/open.c:146 [inline]
__se_sys_truncate fs/open.c:144 [inline]
__x64_sys_truncate+0x31/0x40 fs/open.c:144
x64_sys_call+0x26d0/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:77
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

value changed: 0xffff -> 0x126d

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 7897 Comm: syz.2.1286 Not tainted 6.13.0-rc1-syzkaller-00182-gb8f52214c61a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
==================================================================
FAT-fs (loop2): error, clusters badly computed (4595 != 18)
FAT-fs (loop2): Filesystem has been set read-only
FAT-fs (loop2): error, clusters badly computed (4596 != 19)
FAT-fs (loop2): error, clusters badly computed (4597 != 20)
FAT-fs (loop2): error, clusters badly computed (4598 != 21)
FAT-fs (loop2): error, clusters badly computed (4599 != 22)
FAT-fs (loop2): error, clusters badly computed (4600 != 23)


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[syzbot]

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