Re: [PATCH] audit: fix size of netlink messages

[Eric Paris <eparis@redhat.com>]

On Fri, 2013-06-07 at 17:25 +0200, Nicolas Dichtel wrote:

NAK.

I tried this once before and as I recal userspace actually expected the
stoopidity of being unaligned and broke   :-(

> Netlink messages must be aligned on NLMSG_ALIGNTO (4 bytes), thus we need to
> update the skb length before sending it to userspace.
> 
> This patch adds the needed padding to be compliant with this requirement.
> 
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> ---
>  kernel/audit.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 21c7fa6..31d213a 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1669,6 +1669,17 @@ void audit_log_end(struct audit_buffer *ab)
>  		struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);
>  		nlh->nlmsg_len = ab->skb->len - NLMSG_HDRLEN;
>  
> +		if (NLMSG_ALIGN(ab->skb->len) != ab->skb->len) {
> +			unsigned int pad = NLMSG_ALIGN(ab->skb->len) -
> +					   ab->skb->len;
> +
> +			if (skb_tailroom(ab->skb) >= pad)
> +				skb_put(ab->skb, pad);
> +			else if (pskb_expand_head(ab->skb, 0, pad,
> +						  GFP_KERNEL) < 0)
> +				audit_log_lost("out of memory in audit_log_end");
> +		}
> +
>  		if (audit_pid) {
>  			skb_queue_tail(&audit_skb_queue, ab->skb);
>  			wake_up_interruptible(&kauditd_wait);