Re: [PATCH v2] net/mlx5: Fix possible NULL deref in RX path

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

On Tue, Aug 02, 2016 at 03:02:18PM +0300, Sagi Grimberg wrote:
> The user is allowed to call ->rx_pkt_burst() even without free
> mbufs in the pool. In this scenario we'll fail allocating a rep mbuf
> on the first iteration (where pkt is still NULL). This would cause us
> to deref a NULL pkt (reset refcount and free).
> 
> Fix this by checking the pkt before freeing it.
> 
> Fixes: a1bdb71a32da ("net/mlx5: fix crash in Rx")
> Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
> ---
> Changes from v1:
> - check pkt only once in case we failed to allocate a buffer
> 
>  drivers/net/mlx5/mlx5_rxtx.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
> index fce3381ae87a..37573668e43e 100644
> --- a/drivers/net/mlx5/mlx5_rxtx.c
> +++ b/drivers/net/mlx5/mlx5_rxtx.c
> @@ -1572,6 +1572,14 @@ mlx5_rx_burst(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
>  		rte_prefetch0(wqe);
>  		rep = rte_mbuf_raw_alloc(rxq->mp);
>  		if (unlikely(rep == NULL)) {
> +			++rxq->stats.rx_nombuf;
> +			if (!pkt) {
> +				/*
> +				 * no buffers before we even started,
> +				 * bail out silently.
> +				 */
> +				break;
> +			}
>  			while (pkt != seg) {
>  				assert(pkt != (*rxq->elts)[idx]);
>  				seg = NEXT(pkt);
> @@ -1579,7 +1587,6 @@ mlx5_rx_burst(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
>  				__rte_mbuf_raw_free(pkt);
>  				pkt = seg;
>  			}
> -			++rxq->stats.rx_nombuf;
>  			break;
>  		}
>  		if (!pkt) {
> -- 
> 1.9.1

A few nit-picks from check-git-log.sh:

 Wrong headline uppercase:
         net/mlx5: Fix possible NULL deref in RX path
 Wrong headline lowercase:
         net/mlx5: Fix possible NULL deref in RX path
 Missing blank line after 'Fixes' tag:
         Fixes: a1bdb71a32da ("net/mlx5: fix crash in Rx")

Otherwise,

Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>

-- 
Adrien Mazarguil
6WIND