linux-kernel - Re: [PATCH] fs/ntfs3: fix negative shift size in true_sectors_per

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Date:   Fri, 23 Sep 2022 14:58:21 +0300
From:   Konstantin Komarov <almaz.alexandrovich@...agon-software.com>
To:     Randy Dunlap <rdunlap@...radead.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Namjae Jeon <linkinjeon@...nel.org>,
        Shigeru Yoshida <syoshida@...hat.com>
CC:     syzbot <syzbot+1631f09646bc214d2e76@...kaller.appspotmail.com>,
        <syzkaller-bugs@...glegroups.com>, <ntfs3@...ts.linux.dev>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs/ntfs3: fix negative shift size in
 true_sectors_per_clst()



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@...kaller.appspotmail.com>
>> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
>> Tested-by: syzbot <syzbot+1631f09646bc214d2e76@...kaller.appspotmail.com>
>> 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@redhat.com/
> 
> 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.