[dpdk-dev] [PATCH] net/mlx5: Fix possible NULL deref in RX path
Adrien Mazarguil
adrien.mazarguil at 6wind.com
Tue Aug 2 13:31:29 CEST 2016
On Tue, Aug 02, 2016 at 01:47:55PM +0300, Sagi Grimberg wrote:
>
>
> On 02/08/16 12:58, Adrien Mazarguil wrote:
> >On Tue, Aug 02, 2016 at 12:31:35PM +0300, Sagi Grimberg wrote:
> >>
> >>
> >>On 01/08/16 19:43, Adrien Mazarguil wrote:
> >>>Hi Sagi,
> >>>
> >>>On Mon, Aug 01, 2016 at 11:44:21AM +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.
> >>>
> >>>Just to be sure, did you get an actual NULL deref crash here or is that an
> >>>assumed possibility?
> >>>
> >>>I'm asking because this problem was supposed to be addressed by:
> >>>
> >>>a1bdb71a32da ("net/mlx5: fix crash in Rx")
> >>
> >>I actually got the NULL deref. This happens when the application doesn't
> >>restore mbufs to the pool correctly. In the case rte_mbuf_raw_alloc
> >>will fail on the first iteration (pkt wasn't assigned) unlike the
> >>condition handled in a1bdb71a32da.
> >>
> >>With this applied, I didn't see the crash.
> >
> >Thanks for confirming this,
>
> Hey Adrien, I just noticed that I missed the rest of
> your response in the previous message (pre-coffee mail
> browsing...)
>
> You analysis was on spot.
>
> >now what about the different approach I
> >suggested in my previous message to avoid the extra check in the inner loop:
> >
> > if (!pkt)
> > pkt = seg;
> > while (pkt != seg) {
> > ...
> > }
>
> We can go this way, but it looks kinda confusing to set pkt = seg and
> then iterate on pkt != seg.
>
> How about a more explicit approach:
> --
> 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) {
> --
Yes, that's also fine.
> >Also the fixes line in your commit message?
>
> I'll add it in v2. Thanks.
Go ahead, thanks!
--
Adrien Mazarguil
6WIND
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