WARNING in fat_ent_write

Status: upstream: reported C repro on 2026/10/22 21:25
Reported-by: syzbot+60cc5414d38b2e2f9282@syzkaller.appspotmail.com
First crash: 3d18h, last: 2d04h
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 WARNING in fat_ent_write -1 syz, C 2 2d01h 3d11h 0/3 upstream: reported C repro on 2026/10/23 04:05
upstream WARNING in fat_ent_write prio:low exfat -1 syz 43 10d 63d 2/29 upstream: reported syz repro on 2026/08/24 07:47

Sample crash report:
syz.0.17: attempt to access beyond end of device
loop0: rw=1, sector=1, nr_sectors = 1 limit=0
Buffer I/O error on dev loop0, logical block 1, lost sync page write
------------[ cut here ]------------
WARNING: CPU: 0 PID: 5978 at fs/buffer.c:1188 mark_buffer_dirty+0x2bb/0x4d0 fs/buffer.c:1188
Modules linked in:
CPU: 0 PID: 5978 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
RIP: 0010:mark_buffer_dirty+0x2bb/0x4d0 fs/buffer.c:1188
Code: 00 00 00 5b 41 5c 41 5e 41 5f 5d e9 5f 97 fc ff e8 9a bd 87 ff 48 89 df 5b 41 5c 41 5e 41 5f 5d e9 da f8 e7 ff e8 85 bd 87 ff <0f> 0b e9 84 fd ff ff e8 79 bd 87 ff 0f 0b e9 b0 fd ff ff e8 6d bd
RSP: 0018:ffffc9000316f338 EFLAGS: 00010293
RAX: ffffffff8200165b RBX: ffff88806ee21828 RCX: ffff88802d979e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: ffff8880211f3701 R08: ffff88806ee2182f R09: 1ffff1100ddc4305
R10: dffffc0000000000 R11: ffffed100ddc4306 R12: dffffc0000000000
R13: ffff888062488368 R14: ffffea00017e6e18 R15: 000000000fffffff
FS:  00007fbeec3b26c0(0000) GS:ffff8880b8c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbeeb5ecc40 CR3: 000000007732e000 CR4: 00000000003506f0
Call Trace:
 <TASK>
 mark_buffer_dirty_inode+0x86/0x2c0 fs/buffer.c:681
 fat_ent_write+0xb2/0x180 fs/fat/fatent.c:417
 fat_chain_add+0x3e9/0x890 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+0x765/0xae0 fs/fat/inode.c:190
 __block_write_begin_int+0x571/0x1b00 fs/buffer.c:2124
 __block_write_begin fs/buffer.c:2173 [inline]
 block_write_begin+0x9a/0x1e0 fs/buffer.c:2234
 cont_write_begin+0x5fd/0x800 fs/buffer.c:2591
 fat_write_begin+0x97/0x160 fs/fat/inode.c:230
 generic_perform_write+0x2fe/0x5c0 mm/filemap.c:4027
 generic_file_write_iter+0xaf/0x2e0 mm/filemap.c:4148
 do_iter_readv_writev fs/read_write.c:-1 [inline]
 do_iter_write+0x747/0xc50 fs/read_write.c:860
 vfs_writev fs/read_write.c:933 [inline]
 do_pwritev+0x242/0x3a0 fs/read_write.c:1030
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fbeeb59f559
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:00007fbeec3b2028 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007fbeeb825fa0 RCX: 00007fbeeb59f559
RDX: 0000000000000001 RSI: 0000200000022500 RDI: 0000000000000005
RBP: 00007fbeeb636b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000e7b R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbeeb826038 R14: 00007fbeeb825fa0 R15: 00007fff4383fb18
 </TASK>

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/24 11:00 linux-6.6.y 0aebf2870d53 1d9ca40b .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-linux-6-6-kasan WARNING in fat_ent_write
2026/10/22 21:31 linux-6.6.y 0aebf2870d53 b55fad29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in fat_ent_write
2026/10/22 21:31 linux-6.6.y 0aebf2870d53 b55fad29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in fat_ent_write
2026/10/22 21:28 linux-6.6.y 0aebf2870d53 b55fad29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in fat_ent_write
2026/10/22 21:27 linux-6.6.y 0aebf2870d53 b55fad29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in fat_ent_write
2026/10/22 21:24 linux-6.6.y 0aebf2870d53 b55fad29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in fat_ent_write
* Struck through repros no longer work on HEAD.