syzbot


kernel BUG in ext4_alloc_file_blocks

Status: upstream: reported C repro on 2026/05/13 12:45
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+871c436f735470348e51@syzkaller.appspotmail.com
First crash: 3d01h, last: 3d00h
Bug presence (2)
Date Name Commit Repro Result
2026/05/16 lts (merge base) de8dfb3f0278 C [report] lost connection to test machine
2026/05/16 upstream (ToT) 6916d5703ddf C [report] lost connection to test machine
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream kernel BUG in ext4_alloc_file_blocks ext4 -1 C error error 3 287d 414d 0/29 auto-obsoleted due to no activity on 2026/01/28 09:24
android-6-1 kernel BUG in ext4_alloc_file_blocks origin:lts -1 C error 1 38d 217d 0/2 upstream: reported C repro on 2025/10/10 15:21

Sample crash report:
------------[ cut here ]------------
kernel BUG at fs/ext4/extents.c:4511!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 457 Comm: syz.3.26 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:ext4_alloc_file_blocks+0xb4f/0xb60 fs/ext4/extents.c:4511
Code: 8b 4c 24 10 80 e1 07 fe c1 38 c1 0f 8c 78 f6 ff ff 48 8b 7c 24 10 e8 80 60 d3 ff e9 69 f6 ff ff e8 36 1e d9 02 e8 c1 2a 94 ff <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41
RSP: 0018:ffffc900015f7700 EFLAGS: 00010293
RAX: ffffffff81d5a0af RBX: 0000000000000003 RCX: ffff888116adcf00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900015f7868 R08: ffff888120dcb4ef R09: 1ffff110241b969d
R10: dffffc0000000000 R11: ffffed10241b969e R12: ffff888120dcb4e8
R13: ffff888120dcb5f0 R14: 0000000000000000 R15: 0000000000000000
FS:  00007ffbaa2f76c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffbaa503540 CR3: 0000000112915000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ext4_zero_range+0x449/0xd00 fs/ext4/extents.c:4661
 ext4_fallocate+0x562/0x1de0 fs/ext4/extents.c:4796
 vfs_fallocate+0x4b4/0x590 fs/open.c:309
 ioctl_preallocate fs/ioctl.c:294 [inline]
 file_ioctl fs/ioctl.c:339 [inline]
 do_vfs_ioctl+0x1b84/0x1d80 fs/ioctl.c:853
 __do_sys_ioctl fs/ioctl.c:872 [inline]
 __se_sys_ioctl+0x9f/0x1a0 fs/ioctl.c:860
 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:860
 x64_sys_call+0x2f/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7ffbaa4b5e59
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:00007ffbaa2f7028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffbaa72f090 RCX: 00007ffbaa4b5e59
RDX: 0000200000000180 RSI: 0000000040305839 RDI: 0000000000000005
RBP: 00007ffbaa54bd6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffbaa72f128 R14: 00007ffbaa72f090 R15: 00007ffcc55462e8
 </TASK>
Modules linked in:
---[ end trace 66138ba6e348f037 ]---
RIP: 0010:ext4_alloc_file_blocks+0xb4f/0xb60 fs/ext4/extents.c:4511
Code: 8b 4c 24 10 80 e1 07 fe c1 38 c1 0f 8c 78 f6 ff ff 48 8b 7c 24 10 e8 80 60 d3 ff e9 69 f6 ff ff e8 36 1e d9 02 e8 c1 2a 94 ff <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41
RSP: 0018:ffffc900015f7700 EFLAGS: 00010293
RAX: ffffffff81d5a0af RBX: 0000000000000003 RCX: ffff888116adcf00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900015f7868 R08: ffff888120dcb4ef R09: 1ffff110241b969d
R10: dffffc0000000000 R11: ffffed10241b969e R12: ffff888120dcb4e8
R13: ffff888120dcb5f0 R14: 0000000000000000 R15: 0000000000000000
FS:  00007ffbaa2f76c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001840 CR3: 0000000112915000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/13 13:24 android13-5.15-lts 7f4b368e0410 fec2a7ee .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 kernel BUG in ext4_alloc_file_blocks
2026/05/13 12:44 android13-5.15-lts 7f4b368e0410 fec2a7ee .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 kernel BUG in ext4_alloc_file_blocks
* Struck through repros no longer work on HEAD.