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From:   Anton Altaparmakov <anton@tuxera.com>
To:     Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
CC:     "linux-ntfs-dev@lists.sourceforge.net" 
        <linux-ntfs-dev@lists.sourceforge.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        "syzbot+213ac8bb98f7f4420840@syzkaller.appspotmail.com" 
        <syzbot+213ac8bb98f7f4420840@syzkaller.appspotmail.com>
Subject: Re: [PATCH] ntfs: Fix validity check for file name attribute
Thread-Topic: [PATCH] ntfs: Fix validity check for file name attribute
Thread-Index: AQHXYNr9xtdXtYfpBEGmty8mpcDGlasom2mAgABu7oA=
Date:   Mon, 28 Jun 2021 09:22:53 +0000
Message-ID: <A2D2BB3D-8C89-40D7-B0CF-F1D2B5176152@tuxera.com>
References: <20210614050540.289494-1-desmondcheongzx@gmail.com>
 <ea63e5af-6ac4-08fe-4261-904d55392b10@gmail.com>
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Hi,

Thanks for the patch!  Have asked Andrew to merge it.

Best regards,

	Anton

> On 28 Jun 2021, at 03:45, Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> wrote:
> 
> On 14/6/21 1:05 pm, Desmond Cheong Zhi Xi wrote:
>> When checking the file name attribute, we want to ensure that it fits
>> within the bounds of ATTR_RECORD. To do this, we should check
>> that (attr record + file name offset + file name length) < (attr
>> record + attr record length).
>> However, the original check did not include the file name offset in
>> the calculation. This means that corrupted on-disk metadata might not
>> caught by the incorrect file name check, and lead to an invalid memory
>> access.
>> An example can be seen in the crash report of a memory corruption
>> error found by Syzbot:
>> https://syzkaller.appspot.com/bug?id=a1a1e379b225812688566745c3e2f7242bffc246
>> Adding the file name offset to the validity check fixes this error and
>> passes the Syzbot reproducer test.
>> Reported-by: syzbot+213ac8bb98f7f4420840@syzkaller.appspotmail.com
>> Tested-by: syzbot+213ac8bb98f7f4420840@syzkaller.appspotmail.com
>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
>> ---
>>  fs/ntfs/inode.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
>> index f5c058b3192c..4474adb393ca 100644
>> --- a/fs/ntfs/inode.c
>> +++ b/fs/ntfs/inode.c
>> @@ -477,7 +477,7 @@ static int ntfs_is_extended_system_file(ntfs_attr_search_ctx *ctx)
>>  		}
>>  		file_name_attr = (FILE_NAME_ATTR*)((u8*)attr +
>>  				le16_to_cpu(attr->data.resident.value_offset));
>> -		p2 = (u8*)attr + le32_to_cpu(attr->data.resident.value_length);
>> +		p2 = (u8 *)file_name_attr + le32_to_cpu(attr->data.resident.value_length);
>>  		if (p2 < (u8*)attr || p2 > p)
>>  			goto err_corrupt_attr;
>>  		/* This attribute is ok, but is it in the $Extend directory? */
> 
> Hi Anton,
> 
> Any chance to review this patch?
> 
> Best wishes,
> Desmond


-- 
Anton Altaparmakov <anton at tuxera.com> (replace at with @)
Lead in File System Development, Tuxera Inc., http://www.tuxera.com/
Linux NTFS maintainer