Re: [PATCH] hfs: Fix OOB Write in hfs_asc2mac

[Viacheslav Dubeyko]

> On Nov 30, 2022, at 5:53 PM, zhangpeng (AS) <zhangpeng362@xxxxxxxxxx> wrote:
> 
> 
> On 2022/11/30 3:08, Viacheslav Dubeyko wrote:
>>> On Nov 28, 2022, at 6:23 PM, zhangpeng (AS) <zhangpeng362@xxxxxxxxxx> wrote:
>>> 
>>> On 2022/11/29 3:29, Viacheslav Dubeyko wrote:
>>>>> On Nov 25, 2022, at 8:36 PM, Peng Zhang <zhangpeng362@xxxxxxxxxx> wrote:
>>>>> 
>>>>> From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
>>>>> 
>>>>> Syzbot reported a OOB Write bug:
>>>>> 
>>>>> loop0: detected capacity change from 0 to 64
>>>>> ==================================================================
>>>>> BUG: KASAN: slab-out-of-bounds in hfs_asc2mac+0x467/0x9a0
>>>>> fs/hfs/trans.c:133
>>>>> Write of size 1 at addr ffff88801848314e by task syz-executor391/3632
>>>>> 
>>>>> Call Trace:
>>>>> <TASK>
>>>>> __dump_stack lib/dump_stack.c:88 [inline]
>>>>> dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
>>>>> print_address_description+0x74/0x340 mm/kasan/report.c:284
>>>>> print_report+0x107/0x1f0 mm/kasan/report.c:395
>>>>> kasan_report+0xcd/0x100 mm/kasan/report.c:495
>>>>> hfs_asc2mac+0x467/0x9a0 fs/hfs/trans.c:133
>>>>> hfs_cat_build_key+0x92/0x170 fs/hfs/catalog.c:28
>>>>> hfs_lookup+0x1ab/0x2c0 fs/hfs/dir.c:31
>>>>> lookup_open fs/namei.c:3391 [inline]
>>>>> open_last_lookups fs/namei.c:3481 [inline]
>>>>> path_openat+0x10e6/0x2df0 fs/namei.c:3710
>>>>> do_filp_open+0x264/0x4f0 fs/namei.c:3740
>>>>> 
>>>>> If in->len is much larger than HFS_NAMELEN(31) which is the maximum
>>>>> length of an HFS filename, a OOB Write could occur in hfs_asc2mac(). In
>>>>> that case, when the dst reaches the boundary, the srclen is still
>>>>> greater than 0, which causes a OOB Write.
>>>>> Fix this by adding a Check on dstlen before Writing to dst address.
>>>>> 
>>>>> Fixes: 328b92278650 ("[PATCH] hfs: NLS support")
>>>>> Reported-by: syzbot+dc3b1cf9111ab5fe98e7@xxxxxxxxxxxxxxxxxxxxxxxxx
>>>>> Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx>
>>>>> ---
>>>>> fs/hfs/trans.c | 2 ++
>>>>> 1 file changed, 2 insertions(+)
>>>>> 
>>>>> diff --git a/fs/hfs/trans.c b/fs/hfs/trans.c
>>>>> index 39f5e343bf4d..886158db07b3 100644
>>>>> --- a/fs/hfs/trans.c
>>>>> +++ b/fs/hfs/trans.c
>>>>> @@ -130,6 +130,8 @@ void hfs_asc2mac(struct super_block *sb, struct hfs_name *out, const struct qstr
>>>>> 				dst += size;
>>>>> 				dstlen -= size;
>>>>> 			} else {
>>>>> +				if (dstlen == 0)
>>>>> +					goto out;
>>>> Maybe, it makes sense to use dstlen instead of srclen in while()?
>>>> 
>>>> We have now:
>>>> 
>>>> while (srclen > 0) {
>>>>    <skipped>
>>>> } else {
>>>>    <skipped>
>>>> }
>>>> 
>>>> We can use instead:
>>>> 
>>>> while (dstlen > 0) {
>>>>    <skipped>
>>>> } else {
>>>>    <skipped>
>>>> }
>>>> 
>>>> Will it fix the issue?
>>>> 
>>>> Thanks,
>>>> Slava.
>>> Thank you for your help.
>>> 
>>> After testing, it fix the issue.
>>> Would it be better to add dstlen > 0 instead of replacing srclen > 0 with dstlen > 0?
>>> Because there may be dstlen > 0 and srclen <= 0.
>>> 
>>> we can use:
>>> 
>>> while (srclen > 0 && dstlen > 0) {
>>>   <skipped>
>>> } else {
>>>   <skipped>
>>> }
>>> 
>> Looks good to me.
> 
> Can I put you down as a Reviewed-by or Suggested-by?

Sure. I hope to see the second version of the patch.

Reviewed-by: Viacheslav Dubeyko <slava@xxxxxxxxxxx>

Thanks,
Slava.

> 
> Thanks,
> Zhang Peng
> 
>> Thanks,
>> Slava.
>> 
>>> Thanks,
>>> Zhang Peng
>>> 
>>>>> 				*dst++ = ch > 0xff ? '?' : ch;
>>>>> 				dstlen--;
>>>>> 			}
>>>>> -- 
>>>>> 2.25.1