linux-kernel - Re: [syzbot] [overlayfs?] general protection fault in ovl

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Message-ID: <694abf5f.050a0220.19928e.002f.GAE@google.com>
Date: Tue, 23 Dec 2025 08:12:15 -0800
From: syzbot <syzbot+a16fb0cce329a320661c@...kaller.appspotmail.com>
To: amir73il@...il.com, linux-kernel@...r.kernel.org, 
	linux-unionfs@...r.kernel.org, miklos@...redi.hu, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [overlayfs?] general protection fault in ovl_iterate

syzbot has found a reproducer for the following issue on:

HEAD commit:    8f0b4cce4481 Linux 6.19-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=136ffb58580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8a8594efdc14f07a
dashboard link: https://syzkaller.appspot.com/bug?extid=a16fb0cce329a320661c
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=106bcd84580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14768f1a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cd4f5f43efc8/disk-8f0b4cce.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/aafb35ac3a3c/vmlinux-8f0b4cce.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d221fae4ab17/Image-8f0b4cce.gz.xz

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

Unable to handle kernel paging request at virtual address ffffffffc24a9a90
KASAN: maybe wild-memory-access in range [0x0003fffe1254d480-0x0003fffe1254d487]
Mem abort info:
  ESR = 0x0000000096000006
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x06: level 2 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000206d55000
[ffffffffc24a9a90] pgd=0000000000000000, p4d=000000020aaef403, pud=000000020aaf0403, pmd=0000000000000000
Internal error: Oops: 0000000096000006 [#1]  SMP
Modules linked in:
CPU: 0 UID: 0 PID: 6752 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : ovl_seek_cursor fs/overlayfs/readdir.c:471 [inline]
pc : ovl_iterate_merged fs/overlayfs/readdir.c:851 [inline]
pc : ovl_iterate+0xff8/0x1ca4 fs/overlayfs/readdir.c:906
lr : ovl_cache_get fs/overlayfs/readdir.c:505 [inline]
lr : ovl_iterate_merged fs/overlayfs/readdir.c:845 [inline]
lr : ovl_iterate+0xcbc/0x1ca4 fs/overlayfs/readdir.c:906
sp : ffff80009d567860
x29: ffff80009d567b70 x28: ffff0000c24a9e80 x27: 0000000000000000
x26: 0000000000000000 x25: ffffffffc24a9a80 x24: ffff0000c24a9e88
x23: ffffffffc24a9a90 x22: ffff80009d567cc8 x21: dfff800000000000
x20: ffff0000d55a1a5c x19: ffffffffc24a9a90 x18: 00000000ffffffff
x17: ffff800080df1c30 x16: ffff80008053826c x15: 0000000000000001
x14: 00000000ffff8000 x13: 0000000074bfa048 x12: ffff800080021d9c
x11: ffff800093397d48 x10: 0000000000ff0100 x9 : 860a1b99182b4800
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 000000000000003f
x5 : 0000000000000040 x4 : 0000000000000001 x3 : 0000000000000010
x2 : 0000000000000006 x1 : 0000000000000080 x0 : 0000000000000001
Call trace:
 ovl_seek_cursor fs/overlayfs/readdir.c:471 [inline] (P)
 ovl_iterate_merged fs/overlayfs/readdir.c:851 [inline] (P)
 ovl_iterate+0xff8/0x1ca4 fs/overlayfs/readdir.c:906 (P)
 wrap_directory_iterator+0x90/0xf0 fs/readdir.c:65
 shared_ovl_iterate+0x30/0x40 fs/overlayfs/readdir.c:1065
 iterate_dir+0x2dc/0x478 fs/readdir.c:108
 __do_sys_getdents64 fs/readdir.c:410 [inline]
 __se_sys_getdents64 fs/readdir.c:396 [inline]
 __arm64_sys_getdents64+0x110/0x2fc fs/readdir.c:396
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x5c/0x26c arch/arm64/kernel/entry-common.c:724
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596
Code: 38756908 34000068 aa1703e0 97c3a4c7 (f94002f7) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	38756908 	ldrb	w8, [x8, x21]
   4:	34000068 	cbz	w8, 0x10
   8:	aa1703e0 	mov	x0, x23
   c:	97c3a4c7 	bl	0xffffffffff0e9328
* 10:	f94002f7 	ldr	x23, [x23] <-- trapping instruction


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.