Subject: Re: [PATCH] ip/xfrm: Fix deleteall when having many policies installed

From: Stephen Hemminger <[email-masked]>
Date: Tue, 17 Jan 2017 08:44:12 -0800

On Mon, 16 Jan 2017 15:09:01 +0100
Alexander Heinlein <[email-masked]> wrote:

> Fix "Policy buffer overflow" error when trying to use deleteall with
> many policies installed.
> 
> Signed-off-by: Alexander Heinlein <[email-masked]>
> ---
>  ip/xfrm_policy.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/ip/xfrm_policy.c b/ip/xfrm_policy.c
> index cc9c0f1..451b982 100644
> --- a/ip/xfrm_policy.c
> +++ b/ip/xfrm_policy.c
> @@ -732,10 +732,8 @@ static int xfrm_policy_keep(const struct
> sockaddr_nl *who,
>  	if (!xfrm_policy_filter_match(xpinfo, ptype))
>  		return 0;
> 
> -	if (xb->offset > xb->size) {
> -		fprintf(stderr, "Policy buffer overflow\n");
> -		return -1;
> -	}
> +	if (xb->offset + NLMSG_LENGTH(sizeof(*xpid)) > xb->size)
> +		return 0;
> 
>  	new_n = (struct nlmsghdr *)(xb->buf + xb->offset);
>  	new_n->nlmsg_len = NLMSG_LENGTH(sizeof(*xpid));

What happens when many many policies are installed?
It looks like your patch would silently stop deleting.
Does the the code flush all of them?