Re: [syzbot] [ext4?] general protection fault in __bh_submit

[syzbot <syzbot+41453ea05ab61c075f1f@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    9d80aa4617b3 Add linux-next specific files for 20260903
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15fa38f9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bb4a32c282cc2ec7
dashboard link: https://syzkaller.appspot.com/bug?extid=41453ea05ab61c075f1f
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17c228f9580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13fa38f9580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/417a63e8ac61/disk-9d80aa46.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a1d004c189c1/vmlinux-9d80aa46.xz
kernel image: https://storage.googleapis.com/syzbot-assets/97413e5bd243/bzImage-9d80aa46.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/21b9bcefd2ef/mount_0.gz
  fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=100508f9580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+41453ea05ab61c075f1f@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 UID: 0 PID: 4945 Comm: jbd2/sda1-8 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:const_folio_flags include/linux/page-flags.h:345 [inline]
RIP: 0010:folio_test_dropbehind include/linux/page-flags.h:600 [inline]
RIP: 0010:__bh_submit+0x22d/0x8d0 fs/buffer.c:1109
Code: c1 e8 03 48 89 44 24 18 42 80 3c 20 00 74 08 48 89 df e8 f6 e7 d7 ff 48 89 5c 24 28 48 8b 1b 4c 8d 7b 08 4c 89 f8 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 ff e8 d4 e7 d7 ff 4d 8b 3f 4c 89 fe 48
RSP: 0018:ffffc9000753f868 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffffffff84b9a9a9
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffff8880739467a0
RBP: 0000000000009801 R08: ffff8880739467ff R09: 1ffff1100e728cff
R10: dffffc0000000000 R11: ffffed100e728d00 R12: dffffc0000000000
R13: ffff888073946780 R14: ffff888076b240e0 R15: 0000000000000008
FS:  0000000000000000(0000) GS:ffff888124cc0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffa1d208708 CR3: 000000000eb48000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 jbd2_journal_commit_transaction+0x2285/0x5c80 fs/jbd2/commit.c:751
 kjournald2+0x3bc/0x740 fs/jbd2/journal.c:200
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 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:const_folio_flags include/linux/page-flags.h:345 [inline]
RIP: 0010:folio_test_dropbehind include/linux/page-flags.h:600 [inline]
RIP: 0010:__bh_submit+0x22d/0x8d0 fs/buffer.c:1109
Code: c1 e8 03 48 89 44 24 18 42 80 3c 20 00 74 08 48 89 df e8 f6 e7 d7 ff 48 89 5c 24 28 48 8b 1b 4c 8d 7b 08 4c 89 f8 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 ff e8 d4 e7 d7 ff 4d 8b 3f 4c 89 fe 48
RSP: 0018:ffffc9000753f868 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffffffff84b9a9a9
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffff8880739467a0
RBP: 0000000000009801 R08: ffff8880739467ff R09: 1ffff1100e728cff
R10: dffffc0000000000 R11: ffffed100e728d00 R12: dffffc0000000000
R13: ffff888073946780 R14: ffff888076b240e0 R15: 0000000000000008
FS:  0000000000000000(0000) GS:ffff888124cc0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffa1d208708 CR3: 000000007f076000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	c1 e8 03             	shr    $0x3,%eax
   3:	48 89 44 24 18       	mov    %rax,0x18(%rsp)
   8:	42 80 3c 20 00       	cmpb   $0x0,(%rax,%r12,1)
   d:	74 08                	je     0x17
   f:	48 89 df             	mov    %rbx,%rdi
  12:	e8 f6 e7 d7 ff       	call   0xffd7e80d
  17:	48 89 5c 24 28       	mov    %rbx,0x28(%rsp)
  1c:	48 8b 1b             	mov    (%rbx),%rbx
  1f:	4c 8d 7b 08          	lea    0x8(%rbx),%r15
  23:	4c 89 f8             	mov    %r15,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 20 00       	cmpb   $0x0,(%rax,%r12,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	4c 89 ff             	mov    %r15,%rdi
  34:	e8 d4 e7 d7 ff       	call   0xffd7e80d
  39:	4d 8b 3f             	mov    (%r15),%r15
  3c:	4c 89 fe             	mov    %r15,%rsi
  3f:	48                   	rex.W


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