Re: [win-pv-devel] [PATCH] Avoid possible NULL pointer dereference

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: win-pv-devel [mailto:win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On
> Behalf Of owen.smith@xxxxxxxxxx
> Sent: 03 October 2016 12:53
> To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Owen Smith <owen.smith@xxxxxxxxxx>
> Subject: [win-pv-devel] [PATCH] Avoid possible NULL pointer dereference
> 
> From: Owen Smith <owen.smith@xxxxxxxxxx>

Acked-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> 
> If the packet cache is exhausted and unable to allocate more items, fail
> before attempting to use the pointer. Moves the check to after attempting
> to get a packet cache item.
> 
> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
> ---
>  src/xenvif/receiver.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/src/xenvif/receiver.c b/src/xenvif/receiver.c index
> 07fa642..14ff52a 100644
> --- a/src/xenvif/receiver.c
> +++ b/src/xenvif/receiver.c
> @@ -1198,7 +1198,14 @@ ReceiverRingProcessPacket(
>      // Get a new packet structure that will just contain the header after
>      // parsing. We need to preserve metadata from the original.
> 
> +    status = STATUS_NO_MEMORY;
>      New = __ReceiverRingGetPacket(Ring, TRUE);
> +    if (New == NULL) {
> +        FrontendIncrementStatistic(Frontend,
> +            XENVIF_RECEIVER_FRONTEND_ERRORS,
> +            1);
> +        goto fail1;
> +    }
> 
>      RtlCopyMemory(New,
>                    Packet,
> @@ -1209,14 +1216,6 @@ ReceiverRingProcessPacket(
>      // Override offset to align
>      Packet->Offset = Receiver->IpAlignOffset;
> 
> -    status = STATUS_NO_MEMORY;
> -    if (Packet == NULL) {
> -        FrontendIncrementStatistic(Frontend,
> -                                   XENVIF_RECEIVER_FRONTEND_ERRORS,
> -                                   1);
> -        goto fail1;
> -    }
> -
>      StartVa = MmGetSystemAddressForMdlSafe(&Packet->Mdl,
> NormalPagePriority);
>      ASSERT(StartVa != NULL);
>      StartVa += Packet->Offset;
> --
> 2.8.3
> 
> 
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