linux-ext4 - Re: [PATCH] mmp:fix wrong comparison in ext2fs_mmp

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Date:   Tue, 10 Jan 2023 17:03:24 +0800
From:   "lihaoxiang (F)" <lihaoxiang9@...wei.com>
To:     <tytso@....edu>
CC:     <linux-ext4@...r.kernel.org>,
        Zhiqiang Liu <liuzhiqiang26@...wei.com>,
        <linfeilong@...wei.com>, <louhongxiang@...wei.com>,
        "lijinlin (A)" <lijinlin3@...wei.com>
Subject: Re: [PATCH] mmp:fix wrong comparison in ext2fs_mmp_stop

friendly ping...

On 2022/12/9 11:37, lihaoxiang (F) wrote:
> friendly ping...
> 
> On 2022/11/29 15:02, lihaoxiang (F) wrote:
>> In our knowledge, ext2fs_mmp_stop use to process the rest of work
>> when mmp will finish. Critically, it must check if the mmp block is
>> not changed. But there exist an error in comparing the mmp and mmp_cmp.
>>
>> Look to ext2fs_mmp_read, the assignment of mmp_cmp retrieve from the
>> superblock of disk and it copy to mmp_buf if mmp_buf is not none
>> and not equal to mmp_cmp in the meanwhile. However, ext2fs_mmp_stop
>> pass the no NULL pointer fs->mmp_buf which has possed the mmp info to
>> ext2fs_mmp_read. Consequently, ext2fs_mmp_read override fs->mmp_buf
>> by fs->mmp_cmp so that loss the meaning of comparing themselves
>> after that and worse yet, couldn't judge whether the struct of mmp
>> has changed.
>>
>> In fact, we only need to modify the parameter to NULL pointer for
>> solving this problem.
>>
>> Signed-off-by: lihaoxiang <lihaoxiang9@...wei.com>
>> ---
>>  lib/ext2fs/mmp.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/lib/ext2fs/mmp.c b/lib/ext2fs/mmp.c
>> index 7970aac2..14289706 100644
>> --- a/lib/ext2fs/mmp.c
>> +++ b/lib/ext2fs/mmp.c
>> @@ -407,7 +407,7 @@ errcode_t ext2fs_mmp_stop(ext2_filsys fs)
>>  	    (fs->mmp_buf == NULL) || (fs->mmp_cmp == NULL))
>>  		goto mmp_error;
>>
>> -	retval = ext2fs_mmp_read(fs, fs->super->s_mmp_block, fs->mmp_buf);
>> +	retval = ext2fs_mmp_read(fs, fs->super->s_mmp_block, NULL);
>>  	if (retval)
>>  		goto mmp_error;
>>