Re: [syzbot] UBSAN: shift-out-of-bounds in diAlloc

["Dr. David Alan Gilbert" <dave@treblig.org>]

* syzbot (syzbot+9cd47a3d9ebd6776eb03@syzkaller.appspotmail.com) wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    3db61221f4e8 Merge tag 'io_uring-6.0-2022-09-23' of git://..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1017fb54880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c221af36f6d1d811
> dashboard link: https://syzkaller.appspot.com/bug?extid=9cd47a3d9ebd6776eb03
> 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=12bbd0d4880000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=153195ef080000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+9cd47a3d9ebd6776eb03@syzkaller.appspotmail.com
> 
> loop0: detected capacity change from 0 to 66104
> ================================================================================
> UBSAN: shift-out-of-bounds in fs/jfs/jfs_imap.c:1357:9
> shift exponent 218103809 is too large for 64-bit type 'u64' (aka 'unsigned long long')

My reading of this is that jfs does ~no sanity checking of the
structure read from disk when mounting;

int dbMount(struct inode *ipbmap)
...
  bmp->db_agl2size = le32_to_cpu(dbmp_le->dn_agl2size);

The line that triggers it is:
  agno = BLKTOAG(JFS_IP(pip)->agstart, JFS_SBI(pip->i_sb));

which is:
121:#define BLKTOAG(b,sbi)  ((b) >> ((sbi)->bmap->db_agl2size))

so if the mount is given garbage, then that's what it'll shift by.

this is probably the least of the worries of an unchecked disk structure.

Dave


> CPU: 1 PID: 3607 Comm: syz-executor161 Not tainted 6.0.0-rc6-syzkaller-00291-g3db61221f4e8 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
>  ubsan_epilogue lib/ubsan.c:151 [inline]
>  __ubsan_handle_shift_out_of_bounds+0x33d/0x3b0 lib/ubsan.c:322
>  diAlloc+0x141a/0x1700 fs/jfs/jfs_imap.c:1357
>  ialloc+0x8c/0xa80 fs/jfs/jfs_inode.c:56
>  jfs_create+0x13a/0xb10 fs/jfs/namei.c:92
>  lookup_open fs/namei.c:3413 [inline]
>  open_last_lookups fs/namei.c:3481 [inline]
>  path_openat+0x12d0/0x2df0 fs/namei.c:3688
>  do_filp_open+0x264/0x4f0 fs/namei.c:3718
>  do_sys_openat2+0x124/0x4e0 fs/open.c:1313
>  do_sys_open fs/open.c:1329 [inline]
>  __do_sys_creat fs/open.c:1405 [inline]
>  __se_sys_creat fs/open.c:1399 [inline]
>  __x64_sys_creat+0x11f/0x160 fs/open.c:1399
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f60b0aa1f09
> 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 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffc52136898 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f60b0aa1f09
> RDX: 00007f60b0a60403 RSI: 0000000000000000 RDI: 0000000020000040
> RBP: 00007f60b0a616d0 R08: 0000000000000000 R09: 0000000000000000
> R10: 00007ffc52136760 R11: 0000000000000246 R12: 00000000f8008000
> R13: 0000000000000000 R14: 00080000000000fc R15: 0000000000000000
>  </TASK>
> ================================================================================
> 
> 
> ---
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-- 
 -----Open up your eyes, open up your mind, open up your code -------   
/ Dr. David Alan Gilbert    |       Running GNU/Linux       | Happy  \ 
\        dave @ treblig.org |                               | In Hex /
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