Colin Ian King <colin.k...@canonical.com> writes:
> Hi,
>
> Static analysis with Coverity on today's linux-next has found a
> potential null pointer dereference bug with the following commit:
>
> commit d92e4e6e33c8b19635be70fb8935b627d2e4f8fe
> Author: Petr Machata <pe...@mellanox.com>
> Date: Sun Jun 30 09:04:56 2019 +0300
>
> mlxsw: spectrum: PTP: Support timestamping on Spectrum-1
>
>
> In function: mlxsw_sp1_ptp_packet_finish the offending code is as follows:
>
> /* Between capturing the packet and finishing it, there is a
> window of
> * opportunity for the originating port to go away (e.g. due to a
> * split). Also make sure the SKB device reference is still valid.
> */
> mlxsw_sp_port = mlxsw_sp->ports[local_port];
> if (!mlxsw_sp_port && (!skb->dev || skb->dev == mlxsw_sp_port->dev)) {
> dev_kfree_skb_any(skb);
> return;
> }
>
> If mlxsw_sp_port is null and skb->dev is not-null then the comparison
> "skb->dev == mlxsw_sp_port->dev" ends up with a null pointer dereference.
>
> I think the if statement should be:
>
> if (mlxsw_sp_port && (!skb->dev || skb->dev == mlxsw_sp_port->dev))
>
> ..but I'm not 100% sure as I may be missing something a bit more subtle
> here.
Yes, that line is wrong. It's missing a pair of parens, it should be:
if (!(mlxsw_sp_port && (!skb->dev || skb->dev == mlxsw_sp_port->dev))) {
I.e. I need a port && I need the skb->dev to still refer to that port
(or else be NULL). If that doesn't hold, bail out.
Thanks for the report, I'll spin a fix!
