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

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Date:   Fri, 9 Dec 2022 11:37:37 +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 2022/11/29 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;
>