Re: [syzbot] general protection fault in erofs_bread

[Gao Xiang]

Hi Yue,

On Thu, Oct 20, 2022 at 09:45:41PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    493ffd6605b2 Merge tag 'ucount-rlimits-cleanups-for-v5.19'..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=168c673c880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d19f5d16783f901
> dashboard link: https://syzkaller.appspot.com/bug?extid=3faecbfd845a895c04cb
> compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17fb206a880000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13b166ba880000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/f1ff6481e26f/disk-493ffd66.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/101bd3c7ae47/vmlinux-493ffd66.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/c1b35fb0988a/mount_0.gz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3faecbfd845a895c04cb@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> loop0: detected capacity change from 0 to 264192
> erofs: (device loop0): mounted with root inode @ nid 36.
> general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
> CPU: 0 PID: 3611 Comm: syz-executor373 Not tainted 6.0.0-syzkaller-09423-g493ffd6605b2 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
> RIP: 0010:erofs_bread+0x33/0x760 fs/erofs/data.c:35
> Code: 53 48 83 ec 28 89 cb 41 89 d6 48 89 f5 49 89 fd 49 bc 00 00 00 00 00 fc ff df e8 78 b3 a5 fd 48 83 c5 30 48 89 e8 48 c1 e8 03 <42> 80 3c 20 00 74 08 48 89 ef e8 0e 1e f9 fd 89 5c 24 04 4c 8b 7d
> RSP: 0018:ffffc90003bdf2e0 EFLAGS: 00010206
> RAX: 0000000000000006 RBX: 0000000000000001 RCX: ffff888018de5880
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffc90003bdf4e0
> RBP: 0000000000000030 R08: ffffffff83e25022 R09: ffffc90003bdf4e0
> R10: fffff5200077be9f R11: 1ffff9200077be9c R12: dffffc0000000000
> R13: ffffc90003bdf4e0 R14: 000000007ec94954 R15: 000032487ec94954
> FS:  00005555571fa300(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa00d733260 CR3: 000000007d91f000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  z_erofs_read_fragment fs/erofs/zdata.c:667 [inline]

Could you look into this issue? I think it's a simple issue (the
fragment feature sb flag is not set, but so packed_inode != NULL
needs to be checked in z_erofs_read_fragment()).

Thanks,
Gao Xiang