Re: [PATCH] fs/ntfs3: fix negative shift size in true_sectors_per_clst()

[Randy Dunlap]

Hi,

On 9/23/22 04:58, Konstantin Komarov wrote:
> 
> 
> On 9/23/22 03:38, Randy Dunlap wrote:
>> Hi,
>>
>> On 9/20/22 08:59, Tetsuo Handa wrote:
>>> syzbot is reporting shift-out-of-bounds in true_sectors_per_clst() [1], for
>>> commit a3b774342fa752a5 ("fs/ntfs3: validate BOOT sectors_per_clusters")
>>> did not address that (0 - boot->sectors_per_clusters) < 0 because "u8" was
>>> chosen for type of boot->sectors_per_clusters because 0x80 needs to be
>>> positive in order to support 64K clusters. Use "s8" cast in order to make
>>> sure that (0 - (s8) boot->sectors_per_clusters) > 0.
>>>
>>> Link: https://syzkaller.appspot.com/bug?extid=1631f09646bc214d2e76 [1]
>>> Reported-by: syzbot <syzbot+1631f09646bc214d2e76@xxxxxxxxxxxxxxxxxxxxxxxxx>
>>> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
>>> Tested-by: syzbot <syzbot+1631f09646bc214d2e76@xxxxxxxxxxxxxxxxxxxxxxxxx>
>>> Fixes: a3b774342fa752a5 ("fs/ntfs3: validate BOOT sectors_per_clusters")
>>>
>>> diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
>>> index 47012c9bf505..c7ffd21fb255 100644
>>> --- a/fs/ntfs3/super.c
>>> +++ b/fs/ntfs3/super.c
>>> @@ -672,7 +672,7 @@ static u32 true_sectors_per_clst(const struct NTFS_BOOT *boot)
>>>       if (boot->sectors_per_clusters <= 0x80)
>>>           return boot->sectors_per_clusters;
>>>       if (boot->sectors_per_clusters >= 0xf4) /* limit shift to 2MB max */
>>> -        return 1U << (0 - boot->sectors_per_clusters);
>>> +        return 1U << (0 - (s8) boot->sectors_per_clusters);
>>>       return -EINVAL;
>>>   }
>>>   
>>
>> I slightly prefer the earlier patch:
>>
>> https://lore.kernel.org/all/20220823144625.1627736-1-syoshida@xxxxxxxxxx/
>>
>> but it appears that the NTFS3 maintainer is MIA again. :(
>>
> 
> Hello
> 
> I've sent patches on 12.09, so I'm not MIA.
> I plan to look at patches next week, there are quite a lot of them.

OK, good news. Thanks.

-- 
~Randy