[syzbot] [overlayfs?] general protection fault in ovl_iterate

[syzbot <syzbot+a16fb0cce329a320661c@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    8f0b4cce4481 Linux 6.19-rc1
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=128d7b0a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5888b6002e661229
dashboard link: https://syzkaller.appspot.com/bug?extid=a16fb0cce329a320661c
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/551afd5ea893/disk-8f0b4cce.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1f52c6204286/vmlinux-8f0b4cce.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e55fced475b1/bzImage-8f0b4cce.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a16fb0cce329a320661c@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc9110a1fb76: 0000 [#1] SMP KASAN NOPTI
KASAN: probably user-memory-access in range [0x00000488850fdbb0-0x00000488850fdbb7]
CPU: 0 UID: 0 PID: 25741 Comm: syz.3.5509 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:ovl_iterate_merged fs/overlayfs/readdir.c:856 [inline]
RIP: 0010:ovl_iterate+0x645/0x1120 fs/overlayfs/readdir.c:906
Code: 07 00 00 49 8b 46 08 48 83 c0 10 48 39 c3 0f 84 b0 fd ff ff e8 bc 94 77 fe 4c 8d 63 31 4c 89 e0 4c 89 e2 48 c1 e8 03 83 e2 07 <0f> b6 04 28 38 d0 7f 08 84 c0 0f 85 01 07 00 00 44 0f b6 6b 31 31
RSP: 0018:ffffc90003367d20 EFLAGS: 00010206
RAX: 0000009110a1fb76 RBX: 00000488850fdb85 RCX: ffffc90019118000
RDX: 0000000000000006 RSI: ffffffff83473ee4 RDI: 0000000000000007
RBP: dffffc0000000000 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: ffff888026ca66b0 R12: 00000488850fdbb6
R13: ffff888056ed2598 R14: ffff888033b4e900 R15: ffffc90003367e70
FS:  00007f78892aa6c0(0000) GS:ffff8881248f6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f0c09f72100 CR3: 000000001270e000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 wrap_directory_iterator+0xa2/0xe0 fs/readdir.c:65
 iterate_dir+0x296/0xaf0 fs/readdir.c:108
 __do_sys_getdents fs/readdir.c:326 [inline]
 __se_sys_getdents fs/readdir.c:312 [inline]
 __x64_sys_getdents+0x13c/0x2b0 fs/readdir.c:312
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f788838f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f78892aa038 EFLAGS: 00000246 ORIG_RAX: 000000000000004e
RAX: ffffffffffffffda RBX: 00007f78885e5fa0 RCX: 00007f788838f749
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000007
RBP: 00007f7888413f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f78885e6038 R14: 00007f78885e5fa0 R15: 00007ffe66aedea8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ovl_iterate_merged fs/overlayfs/readdir.c:856 [inline]
RIP: 0010:ovl_iterate+0x645/0x1120 fs/overlayfs/readdir.c:906
Code: 07 00 00 49 8b 46 08 48 83 c0 10 48 39 c3 0f 84 b0 fd ff ff e8 bc 94 77 fe 4c 8d 63 31 4c 89 e0 4c 89 e2 48 c1 e8 03 83 e2 07 <0f> b6 04 28 38 d0 7f 08 84 c0 0f 85 01 07 00 00 44 0f b6 6b 31 31
RSP: 0018:ffffc90003367d20 EFLAGS: 00010206
RAX: 0000009110a1fb76 RBX: 00000488850fdb85 RCX: ffffc90019118000
RDX: 0000000000000006 RSI: ffffffff83473ee4 RDI: 0000000000000007
RBP: dffffc0000000000 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: ffff888026ca66b0 R12: 00000488850fdbb6
R13: ffff888056ed2598 R14: ffff888033b4e900 R15: ffffc90003367e70
FS:  00007f78892aa6c0(0000) GS:ffff8881249f6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055e2adb4d000 CR3: 000000001270e000 CR4: 0000000000350ef0
----------------
Code disassembly (best guess), 1 bytes skipped:
   0:	00 00                	add    %al,(%rax)
   2:	49 8b 46 08          	mov    0x8(%r14),%rax
   6:	48 83 c0 10          	add    $0x10,%rax
   a:	48 39 c3             	cmp    %rax,%rbx
   d:	0f 84 b0 fd ff ff    	je     0xfffffdc3
  13:	e8 bc 94 77 fe       	call   0xfe7794d4
  18:	4c 8d 63 31          	lea    0x31(%rbx),%r12
  1c:	4c 89 e0             	mov    %r12,%rax
  1f:	4c 89 e2             	mov    %r12,%rdx
  22:	48 c1 e8 03          	shr    $0x3,%rax
  26:	83 e2 07             	and    $0x7,%edx
* 29:	0f b6 04 28          	movzbl (%rax,%rbp,1),%eax <-- trapping instruction
  2d:	38 d0                	cmp    %dl,%al
  2f:	7f 08                	jg     0x39
  31:	84 c0                	test   %al,%al
  33:	0f 85 01 07 00 00    	jne    0x73a
  39:	44 0f b6 6b 31       	movzbl 0x31(%rbx),%r13d
  3e:	31                   	.byte 0x31


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