[syzbot] [ext4?] general protection fault in ext4_split_extent_at

[syzbot] [ext4?] general protection fault in ext4_split_extent_at

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    1c9982b49613 Merge tag 'drm-fixes-2026-03-14' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15e35d52580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ccef46afa67b2b19
dashboard link: https://syzkaller.appspot.com/bug?extid=1ffa5d865557e51cb604
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-1c9982b4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0ac9f4872167/vmlinux-1c9982b4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bdee9f3a13ab/bzImage-1c9982b4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1ffa5d865557e51cb604@syzkaller.appspotmail.com

EXT4-fs (loop0): pa ffff88804798e658: logic 0, phys. 209, len 19
EXT4-fs error (device loop0): ext4_mb_release_inode_pa:5465: group 0, free 0, pa_free 8
EXT4-fs error (device loop0): ext4_ext_split:1151: inode #18: comm kworker/u4:8: eh_entries 0 != eh_max 84!
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 UID: 0 PID: 1060 Comm: kworker/u4:8 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
RIP: 0010:ext4_split_extent_at+0x486/0xa40 fs/ext4/extents.c:3266
Code: 02 00 00 e8 0c 90 42 ff 49 bf 00 00 00 00 00 fc ff df 4c 8b 6c 24 38 0f b7 9c 24 e4 00 00 00 49 83 c4 04 4c 89 e0 48 c1 e8 03 <42> 0f b6 04 38 84 c0 0f 85 23 05 00 00 66 41 89 1c 24 4c 8b 74 24
RSP: 0018:ffffc90001567180 EFLAGS: 00010247
RAX: 0000000000000000 RBX: 0000000000008004 RCX: ffff8880331d4980
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900015672c8 R08: ffff888047a501d7 R09: 1ffff11008f4a03a
R10: dffffc0000000000 R11: ffffed1008f4a03b R12: 0000000000000004
R13: 1ffff920002ace44 R14: ffff8880368d5500 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff88808ca55000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007feb2c215ff8 CR3: 00000000123cf000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 ext4_split_extent fs/ext4/extents.c:3440 [inline]
 ext4_split_convert_extents+0x36d/0x1a00 fs/ext4/extents.c:3830
 ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3906 [inline]
 ext4_ext_handle_unwritten_extents fs/ext4/extents.c:3990 [inline]
 ext4_ext_map_blocks+0xe70/0x58b0 fs/ext4/extents.c:4327
 ext4_map_create_blocks+0x11d/0x540 fs/ext4/inode.c:616
 ext4_map_blocks+0x7cd/0x11d0 fs/ext4/inode.c:809
 ext4_convert_unwritten_extents+0x2be/0x5f0 fs/ext4/extents.c:5029
 ext4_convert_unwritten_io_end_vec+0xff/0x170 fs/ext4/extents.c:5069
 ext4_end_io_end+0xc7/0x410 fs/ext4/page-io.c:200
 ext4_do_flush_completed_IO fs/ext4/page-io.c:291 [inline]
 ext4_end_io_rsv_work+0x26a/0x340 fs/ext4/page-io.c:306
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ext4_split_extent_at+0x486/0xa40 fs/ext4/extents.c:3266
Code: 02 00 00 e8 0c 90 42 ff 49 bf 00 00 00 00 00 fc ff df 4c 8b 6c 24 38 0f b7 9c 24 e4 00 00 00 49 83 c4 04 4c 89 e0 48 c1 e8 03 <42> 0f b6 04 38 84 c0 0f 85 23 05 00 00 66 41 89 1c 24 4c 8b 74 24
RSP: 0018:ffffc90001567180 EFLAGS: 00010247
RAX: 0000000000000000 RBX: 0000000000008004 RCX: ffff8880331d4980
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900015672c8 R08: ffff888047a501d7 R09: 1ffff11008f4a03a
R10: dffffc0000000000 R11: ffffed1008f4a03b R12: 0000000000000004
R13: 1ffff920002ace44 R14: ffff8880368d5500 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff88808ca55000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007feb2c215ff8 CR3: 00000000123cf000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
   0:	02 00                	add    (%rax),%al
   2:	00 e8                	add    %ch,%al
   4:	0c 90                	or     $0x90,%al
   6:	42 ff 49 bf          	rex.X decl -0x41(%rcx)
   a:	00 00                	add    %al,(%rax)
   c:	00 00                	add    %al,(%rax)
   e:	00 fc                	add    %bh,%ah
  10:	ff                   	lcall  (bad)
  11:	df 4c 8b 6c          	fisttps 0x6c(%rbx,%rcx,4)
  15:	24 38                	and    $0x38,%al
  17:	0f b7 9c 24 e4 00 00 	movzwl 0xe4(%rsp),%ebx
  1e:	00
  1f:	49 83 c4 04          	add    $0x4,%r12
  23:	4c 89 e0             	mov    %r12,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 0f b6 04 38       	movzbl (%rax,%r15,1),%eax <-- trapping instruction
  2f:	84 c0                	test   %al,%al
  31:	0f 85 23 05 00 00    	jne    0x55a
  37:	66 41 89 1c 24       	mov    %bx,(%r12)
  3c:	4c                   	rex.WR
  3d:	8b                   	.byte 0x8b
  3e:	74 24                	je     0x64


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup