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Message-ID: <1e9159c8-48f5-cf1d-bc5a-e7e33ec0bf04@infradead.org>
Date:   Fri, 23 Sep 2022 09:07:54 -0700
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Subject: Re: [PATCH] fs/ntfs3: fix negative shift size in
 true_sectors_per_clst()
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To:     Konstantin Komarov <almaz.alexandrovich@paragon-software.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Andrew Morton <akpm@linux-foundation.org>,
        Namjae Jeon <linkinjeon@kernel.org>,
        Shigeru Yoshida <syoshida@redhat.com>
Cc:     syzbot <syzbot+1631f09646bc214d2e76@syzkaller.appspotmail.com>,
        syzkaller-bugs@googlegroups.com, ntfs3@lists.linux.dev,
        LKML <linux-kernel@vger.kernel.org>
References: <000000000000f8b5ef05dd25b963@google.com>
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 <1bf6d8ea-9e81-f65a-d7dc-6e94fa12da7b@paragon-software.com>
From:   Randy Dunlap <rdunlap@infradead.org>
In-Reply-To: <1bf6d8ea-9e81-f65a-d7dc-6e94fa12da7b@paragon-software.com>
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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@syzkaller.appspotmail.com>
>>> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>>> Tested-by: syzbot <syzbot+1631f09646bc214d2e76@syzkaller.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.

OK, good news. Thanks.

-- 
~Randy