Message-ID: <CAOQ4uxgkpi4v3NTSTq5GGJEceHHi97iY4rtsAJuo5c-yxu-Bzg@mail.gmail.com>
Date: Fri, 26 Sep 2025 10:22:01 +0200
From: Amir Goldstein <amir73il@...il.com>
To: syzbot <syzbot+f754e01116421e9754b9@...kaller.appspotmail.com>, 
	Phillip Lougher <phillip@...ashfs.org.uk>
Cc: linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org, 
	miklos@...redi.hu, syzkaller-bugs@...glegroups.com, 
	squashfs-devel@...ts.sourceforge.net
Subject: Re: [syzbot] [overlayfs?] WARNING in ovl_copy_up_file (2)

On Thu, Sep 25, 2025 at 7:50 PM syzbot
<syzbot+f754e01116421e9754b9@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    bf40f4b87761 Merge tag 'probes-fixes-v6.17-rc7' of git://g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1636e142580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=bf99f2510ef92ba5
> dashboard link: https://syzkaller.appspot.com/bug?extid=f754e01116421e9754b9
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13eb34e2580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10ca2f12580000
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-bf40f4b8.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/2fe4635de41e/vmlinux-bf40f4b8.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/acfb085eaa3e/bzImage-bf40f4b8.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/1280fcf9f9a9/mount_0.gz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+f754e01116421e9754b9@...kaller.appspotmail.com
>
> loop0: detected capacity change from 0 to 8
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 5501 at fs/overlayfs/copy_up.c:276 ovl_copy_up_file+0x640/0x6a0 fs/overlayfs/copy_up.c:276
> Modules linked in:
> CPU: 0 UID: 0 PID: 5501 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> RIP: 0010:ovl_copy_up_file+0x640/0x6a0 fs/overlayfs/copy_up.c:276
> Code: e9 2d ff ff ff e8 60 ac 8b fe 49 bc 00 00 00 00 00 fc ff df e9 14 ff ff ff e8 4c ac 8b fe 90 0f 0b 90 eb 09 e8 41 ac 8b fe 90 <0f> 0b 90 41 bd fb ff ff ff 48 8b 5c 24 10 e9 8d fb ff ff e8 d8 35
> RSP: 0018:ffffc90002b0f040 EFLAGS: 00010293
> RAX: ffffffff833410ff RBX: ffffc90002b0f0c0 RCX: ffff88801f022440
> RDX: 0000000000000000 RSI: fc0000000000000a RDI: 0000000000000000
> RBP: ffffc90002b0f170 R08: ffffc90002b0f0cf R09: 0000000000000000
> R10: ffffc90002b0f0c0 R11: fffff52000561e1a R12: dffffc0000000000
> R13: fc0000000000000a R14: ffff888033b7d380 R15: ffff888042c0f028
> FS:  0000555584fee500(0000) GS:ffff88808d007000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f2eacb909c0 CR3: 0000000059e0d000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  ovl_copy_up_tmpfile fs/overlayfs/copy_up.c:885 [inline]
>  ovl_do_copy_up fs/overlayfs/copy_up.c:999 [inline]
>  ovl_copy_up_one fs/overlayfs/copy_up.c:1202 [inline]
>  ovl_copy_up_flags+0x1502/0x2fe0 fs/overlayfs/copy_up.c:1257
>  ovl_open+0x138/0x2f0 fs/overlayfs/file.c:211
>  do_dentry_open+0x953/0x13f0 fs/open.c:965
>  vfs_open+0x3b/0x340 fs/open.c:1095
>  do_open fs/namei.c:3887 [inline]
>  path_openat+0x2ee5/0x3830 fs/namei.c:4046
>  do_filp_open+0x1fa/0x410 fs/namei.c:4073
>  do_sys_openat2+0x121/0x1c0 fs/open.c:1435
>  do_sys_open fs/open.c:1450 [inline]
>  __do_sys_openat fs/open.c:1466 [inline]
>  __se_sys_openat fs/open.c:1461 [inline]
>  __x64_sys_openat+0x138/0x170 fs/open.c:1461
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f1be718eec9
> 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:00007fff614ed578 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
> RAX: ffffffffffffffda RBX: 00007f1be73e5fa0 RCX: 00007f1be718eec9
> RDX: 0000000000000042 RSI: 0000200000000040 RDI: ffffffffffffff9c
> RBP: 00007f1be7211f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f1be73e5fa0 R14: 00007f1be73e5fa0 R15: 0000000000000004
>  </TASK>
>
>
> ---
> 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@...glegroups.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 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.
>
> 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)
>

#syz set subsystems: squashfs

It looks like a hand crafted squashfs image returns a negative
value for st_size from stat().

overlayfs is rightly asserting about this and returns -EIO for
the copy up.

I don't feel like the ovl assertion should be removed, but rather the
squashfs bug needs to be fixed.

Thanks,
Amir.

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