Re: [PATCH] mm/backing-dev.c: check user buffer length before copy data to the related user buffer.

[Jan Kara <jack@suse.cz>]

On Tue 20-08-13 11:23:24, Chen Gang wrote:
> '*lenp' may be less than "sizeof(kbuf)", need check it before the next
> copy_to_user().
> 
> pdflush_proc_obsolete() is called by sysctl which 'procname' is
> "nr_pdflush_threads", if the user passes buffer length less than
> "sizeof(kbuf)", it will cause issue.
> 
  Good catch. The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>

								Honza
> 
> Signed-off-by: Chen Gang <gang.chen@asianux.com>
> ---
>  mm/backing-dev.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index e04454c..2674671 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -649,7 +649,7 @@ int pdflush_proc_obsolete(struct ctl_table *table, int write,
>  {
>  	char kbuf[] = "0\n";
>  
> -	if (*ppos) {
> +	if (*ppos || *lenp < sizeof(kbuf)) {
>  		*lenp = 0;
>  		return 0;
>  	}
> -- 
> 1.7.7.6
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

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