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Date:   Thu, 10 Nov 2022 11:27:16 -0600
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Subject: Re: [syzbot] UBSAN: shift-out-of-bounds in diAlloc
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To:     "Dr. David Alan Gilbert" <dave@treblig.org>,
        syzbot <syzbot+9cd47a3d9ebd6776eb03@syzkaller.appspotmail.com>
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 <Y1812bdYPcOn4lll@gallifrey>
From:   Dave Kleikamp <dave.kleikamp@oracle.com>
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On 10/30/22 9:41PM, Dr. David Alan Gilbert wrote:
> * 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;

Yeah, all of code reading data structures at mount time should be 
scrutinized to make sanity checks on the data. The code is just too 
trusting. I'll try to find time to go through it all in the near future, 
but I will appreciate any patches submitted by others as well.

I'll also make a better attempt to be more responsive and not let these 
things sit for several weeks or more.

Thanks,
Shaggy

> 
> 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>
>> ================================================================================
>>
>>
>> ---
>> 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@googlegroups.com.
>>
>> syzbot will keep track of this issue. See:
>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>> syzbot can test patches for this issue, for details see:
>> https://goo.gl/tpsmEJ#testing-patches