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

Konstantin Komarov
2022-09-23T12:03:48Z

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.