Re: [PATCH 1/1] cgroups: strcpy destination string overflow

[Andrew Morton <akpm@linux-foundation.org>]

On Tue,  5 Oct 2010 12:38:05 +0400
Evgeny Kuznetsov <EXT-Eugeny.Kuznetsov@nokia.com> wrote:

> From: Evgeny Kuznetsov <ext-eugeny.kuznetsov@nokia.com>
> 
> Function "strcpy" is used without check for maximum allowed source
> string length and could cause destination string overflow.
> Check for string length is added before using "strcpy".
> Function now is return error if source string length is more than
> a maximum.
> 
> Signed-off-by: Evgeny Kuznetsov <EXT-Eugeny.Kuznetsov@nokia.com>
> ---
>  kernel/cgroup.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index c9483d8..82bbede 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1883,6 +1883,8 @@ static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
>  				      const char *buffer)
>  {
>  	BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
> +	if (strlen(buffer) >= PATH_MAX)
> +		return -EINVAL;
>  	if (!cgroup_lock_live_group(cgrp))
>  		return -ENODEV;
>  	strcpy(cgrp->root->release_agent_path, buffer);

I don't think this can happen, because cftype.max_write_len is
PATH_MAX.

But it's pretty unobvious if this is actually true, and the code is
fragile against future changes.