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
Fix commit: fat: fix fat_ent_write() for reverting the value
Patched on: [ci-upstream-linux-next-kasan-gce-root ci-upstream-rust-kasan-gce], missing on: [ci-qemu-gce-upstream-auto ci-qemu-native-arm64-kvm ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb]
First crash: 51d, last: 2h07m
▶ ▼ ✨ 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 (2)
Title Replies (including bot) Last reply
[PATCH] fat: Fix fat_ent_write() for reverting the value 1 (1) 2026/08/25 12:11
[syzbot] [exfat?] WARNING in fat12_ent_put 1 (2) 2026/08/17 06:50
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 WARNING in fat12_ent_put -1 syz, C 5 1d01h 1d05h 0/3 upstream: reported C repro on 2026/10/01 20:37

Sample crash report:
------------[ cut here ]------------
!buffer_uptodate(bh)
WARNING: fs/buffer.c:991 at mark_buffer_dirty+0x299/0x410 fs/buffer.c:991, CPU#1: syz.1.4140/20972
Modules linked in:
CPU: 1 UID: 0 PID: 20972 Comm: syz.1.4140 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2026
RIP: 0010:mark_buffer_dirty+0x299/0x410 fs/buffer.c:991
Code: 4c 89 f7 e8 69 fa d7 ff 49 8b 3e be 40 00 00 00 5b 41 5c 41 5e 41 5f 5d e9 74 52 fb ff e8 0f f7 67 ff eb 8c e8 08 f7 67 ff 90 <0f> 0b 90 e9 a5 fd ff ff e8 fa f6 67 ff 90 0f 0b 90 e9 cf fd ff ff
RSP: 0018:ffffc9000e457438 EFLAGS: 00010287
RAX: ffffffff825ff428 RBX: ffff888050a499a0 RCX: 0000000000080000
RDX: ffffc90005ce9000 RSI: 000000000000788f RDI: 0000000000007890
RBP: dffffc0000000001 R08: ffff888050a499a7 R09: 1ffff1100a149334
R10: dffffc0000000000 R11: ffffed100a149335 R12: dffffc0000000000
R13: 1ffff92001c8aebe R14: ffffc9000e4575f0 R15: ffff888068033a08
FS:  00007f85f700c6c0(0000) GS:ffff888124dc8000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056049123c950 CR3: 0000000063e61000 CR4: 0000000000350ef0
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
 generic_perform_write+0x2d5/0x8f0 mm/filemap.c:4374
 generic_file_write_iter+0xae/0x330 mm/filemap.c:4517
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x612/0xba0 fs/read_write.c:687
 ksys_write+0x150/0x270 fs/read_write.c:739
 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: 0033:0x7f85f619e159
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:00007f85f700c028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f85f6425fa0 RCX: 00007f85f619e159
RDX: 00000000fffffceb RSI: 00002000000001c0 RDI: 0000000000000005
RBP: 00007f85f623506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f85f6426038 R14: 00007f85f6425fa0 R15: 00007ffd206bc828
 </TASK>

Crashes (25):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/01 11:06 upstream 551c722f4080 38f7f0d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root WARNING in fat12_ent_put
2026/10/03 00:20 upstream 5e0f8396d480 57bbd979 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 23:07 upstream 5e0f8396d480 57bbd979 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 23:07 upstream 5e0f8396d480 57bbd979 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 23:06 upstream 5e0f8396d480 57bbd979 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 23:05 upstream 5e0f8396d480 57bbd979 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 23:05 upstream 5e0f8396d480 57bbd979 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 23:05 upstream 5e0f8396d480 57bbd979 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 23:05 upstream 5e0f8396d480 57bbd979 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 17:28 upstream ce1e0223d8ad 1065c8fa .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 16:55 upstream ce1e0223d8ad 1065c8fa .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 14:37 upstream ce1e0223d8ad 1065c8fa .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 14:37 upstream ce1e0223d8ad 1065c8fa .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 08:44 upstream ce1e0223d8ad 1065c8fa .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 06:03 upstream d24e8ac715de 6d32eb1f .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 06:03 upstream d24e8ac715de 6d32eb1f .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/02 04:31 upstream d24e8ac715de 6d32eb1f .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/01 21:10 upstream d24e8ac715de 6d32eb1f .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/01 16:14 upstream 551c722f4080 38f7f0d1 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/01 15:07 upstream 551c722f4080 38f7f0d1 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/01 10:46 upstream 551c722f4080 38f7f0d1 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/10/01 10:46 upstream 551c722f4080 38f7f0d1 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/08/20 08:11 upstream a4ff2be345d0 1e72964b .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
2026/08/19 23:29 upstream bd5f485f3f02 1e72964b .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in fat12_ent_put
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.