Re: [dpdk-dev] [PATCH] ether: check the first segment length on SW VLAN insertion

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 27 May 2020 15:31:41 +0100
Andrew Rybchenko <arybchenko@solarflare.com> wrote:

> SW VLAN insertion relies on Ethernet addresses location in contigous
> memory (do not split across mbuf segments). There is no any formal
> requirements on data location and mbuf structure which guarantee it.
> So, check it explicitly to avoid corrupted packets if the condition
> is violated. Typically software VLAN insertion is done on Tx prepare
> stage and application will get indication that the packet is invalid
> and cannot be transmitted.
> 
> Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
> ---
>  lib/librte_net/rte_ether.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/lib/librte_net/rte_ether.h b/lib/librte_net/rte_ether.h
> index 0ae4e75b6c..d7c076bba8 100644
> --- a/lib/librte_net/rte_ether.h
> +++ b/lib/librte_net/rte_ether.h
> @@ -357,6 +357,10 @@ static inline int rte_vlan_insert(struct rte_mbuf **m)
>  	if (!RTE_MBUF_DIRECT(*m) || rte_mbuf_refcnt_read(*m) > 1)
>  		return -EINVAL;
>  
> +	/* Can't insert header if the first segment is too short */
> +	if (rte_pktmbuf_data_len(*m) < 2 * RTE_ETHER_ADDR_LEN)
> +		return -EINVAL;

Looks good, but you could also make it handle the fragment case with:

diff --git a/lib/librte_net/rte_ether.h b/lib/librte_net/rte_ether.h
index 0ae4e75b6c58..4d0e310a4fac 100644
--- a/lib/librte_net/rte_ether.h
+++ b/lib/librte_net/rte_ether.h
@@ -350,14 +350,18 @@ static inline int rte_vlan_strip(struct rte_mbuf *m)
  */
 static inline int rte_vlan_insert(struct rte_mbuf **m)
 {
-	struct rte_ether_hdr *oh, *nh;
+	struct rte_ether_hdr *nh, tmp;
+	const struct rte_ether_hdr *oh;
 	struct rte_vlan_hdr *vh;
 
 	/* Can't insert header if mbuf is shared */
 	if (!RTE_MBUF_DIRECT(*m) || rte_mbuf_refcnt_read(*m) > 1)
 		return -EINVAL;
 
-	oh = rte_pktmbuf_mtod(*m, struct rte_ether_hdr *);
+	oh = rte_pktmbuf_read(*m, 0, sizeof(*oh), &tmp);
+	if (unlikely(oh == NULL))
+		return -EINVAL;
+
 	nh = (struct rte_ether_hdr *)
 		rte_pktmbuf_prepend(*m, sizeof(struct rte_vlan_hdr));
 	if (nh == NULL)