WARNING in fat12_ent_put

Status: upstream: reported on 2026/08/17 02:15
Subsystems: exfat
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+e64c6472a3d96a75172a@syzkaller.appspotmail.com
First crash: 4d21h, last: 4d21h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
c67c8adc assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ❌ VMGuestTrigger: ✅ VMHostTrigger: ❌ WARNING in fat12_ent_put 2026/08/15 01:00 2026/08/15 01:00 2026/08/15 01:59 746171ee
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [exfat?] WARNING in fat12_ent_put 1 (2) 2026/08/17 06:50

Sample crash report:
Buffer I/O error on dev loop0, logical block 1, lost sync page write
------------[ cut here ]------------
!buffer_uptodate(bh)
WARNING: fs/buffer.c:991 at mark_buffer_dirty+0x299/0x410 fs/buffer.c:991, CPU#1: syz.0.824/10458
Modules linked in:
CPU: 1 UID: 0 PID: 10458 Comm: syz.0.824 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:mark_buffer_dirty+0x299/0x410 fs/buffer.c:991
Code: 4c 89 f7 e8 49 11 d8 ff 49 8b 3e be 40 00 00 00 5b 41 5c 41 5e 41 5f 5d e9 34 53 fb ff e8 9f a3 69 ff eb 8c e8 98 a3 69 ff 90 <0f> 0b 90 e9 a5 fd ff ff e8 8a a3 69 ff 90 0f 0b 90 e9 cf fd ff ff
RSP: 0018:ffffc900065273f8 EFLAGS: 00010287
RAX: ffffffff825e07c8 RBX: ffff888056e9e460 RCX: 0000000000080000
RDX: ffffc90003f49000 RSI: 0000000000001234 RDI: 0000000000001235
RBP: dffffc0000000001 R08: ffff888056e9e467 R09: 1ffff1100add3c8c
R10: dffffc0000000000 R11: ffffed100add3c8d R12: dffffc0000000000
R13: 1ffff92000ca4eb6 R14: ffffc900065275b0 R15: ffff888050e4ccf8
FS:  00007fe3dc5436c0(0000) GS:ffff888124dfc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2e6edff8 CR3: 000000007c12c000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 mmb_mark_buffer_dirty+0x2c/0x1f0 fs/buffer.c:624
 fat12_ent_put+0x1b7/0x2f0 fs/fat/fatent.c:173
 fat_ent_write+0xb8/0x190 fs/fat/fatent.c:422
 fat_chain_add+0x409/0x8e0 fs/fat/misc.c:140
 fat_add_cluster fs/fat/inode.c:113 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x768/0xae0 fs/fat/inode.c:190
 __block_write_begin_int+0x6c2/0x1900 fs/buffer.c:2030
 block_write_begin fs/buffer.c:2144 [inline]
 cont_write_begin+0x71b/0xac0 fs/buffer.c:2506
 fat_write_begin+0x7a/0x150 fs/fat/inode.c:230
 cont_expand_zero fs/buffer.c:2434 [inline]
 cont_write_begin+0x2d6/0xac0 fs/buffer.c:2496
 fat_write_begin+0x7a/0x150 fs/fat/inode.c:230
 generic_cont_expand_simple+0x146/0x210 fs/buffer.c:2397
 fat_cont_expand+0x61/0x1f0 fs/fat/file.c:226
 fat_fallocate+0x22f/0x2f0 fs/fat/file.c:304
 vfs_fallocate+0x65a/0x7e0 fs/open.c:338
 ksys_fallocate fs/open.c:362 [inline]
 __do_sys_fallocate fs/open.c:367 [inline]
 __se_sys_fallocate fs/open.c:365 [inline]
 __x64_sys_fallocate+0xbf/0x110 fs/open.c:365
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe3db59e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe3dc543028 EFLAGS: 00000246 ORIG_RAX: 000000000000011d
RAX: ffffffffffffffda RBX: 00007fe3db825fa0 RCX: 00007fe3db59e0d9
RDX: 0000000000000009 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007fe3db635024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000010001 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe3db826038 R14: 00007fe3db825fa0 R15: 00007fffaef17d98
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/13 02:08 linux-next 28d012efb432 7ae4acc7 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root WARNING in fat12_ent_put
* Struck through repros no longer work on HEAD.