Re: [PATCH] Avoid dereferencing NULL cache objects.

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 22/08/2023 12:28, Owen Smith wrote:
> XENBUS_CACHE(Get, ...) can fail in low memory conditions. Avoid dereferencing
> NULL pointers in ASSERTs
> Fix up error path to avoid returning a NULL pointer to the cache.
>
> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxx>
> ---
>   src/xenvif/receiver.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
Reviewed-by: Paul Durrant <paul@xxxxxxx>

We should probably accompany this with a warning in CacheFill() if it 
breaks out early due to a slab allocation failure.
> diff --git a/src/xenvif/receiver.c b/src/xenvif/receiver.c
> index 4807582..0ce5b67 100644
> --- a/src/xenvif/receiver.c
> +++ b/src/xenvif/receiver.c
> @@ -266,6 +266,8 @@ __ReceiverRingGetPacket(
>                             &Receiver->CacheInterface,
>                             Ring->PacketCache,
>                             Locked);
> +    if (Packet == NULL)
> +        return NULL;
>   
>       ASSERT(IsZeroMemory(&Packet->Info, sizeof (XENVIF_PACKET_INFO)));
>       ASSERT3P(Packet->Ring, ==, Ring);
> @@ -1788,11 +1790,11 @@ __ReceiverRingPreparePacket(
>   fail2:
>       Error("fail2\n");
>   
> +    __ReceiverRingPutFragment(Ring, Fragment);
> +
>   fail1:
>       Error("fail1 (%08x)\n", status);
>   
> -    __ReceiverRingPutFragment(Ring, Fragment);
> -
>       return NULL;
>   }
>