octeon_ep: Add SKB allocation failures handling in __octep_oq_process_rx()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: octeon_ep: Add SKB allocation failures handling in __octep_oq_process_rx() build_skb() returns NULL in case of a memory allocation failure so handle it inside __octep_oq_process_rx() to avoid NULL pointer dereference. __octep_oq_process_rx() is called during NAPI polling by the driver. If skb allocation fails, keep on pulling packets out of the Rx DMA queue: we shouldn't break the polling immediately and thus falsely indicate to the octep_napi_poll() that the Rx pressure is going down. As there is no associated skb in this case, don't process the packets and don't push them up the network stack - they are skipped. Helper function is implemented to unmmap/flush all the fragment buffers used by the dropped packet. 'alloc_failures' counter is incremented to mark the skb allocation error in driver statistics. Found by Linux Verification Center (linuxtesting.org) with SVACE.

References

• https://git.kernel.org/stable/c/09ce491112bbf0b866e2638d3e961c1c73d1f00b
• https://git.kernel.org/stable/c/c2d2dc4f88bb3cfc4f3cc320fd3ff51b0ae5b0ea
• https://git.kernel.org/stable/c/2dedcb6f99f4c1a11944e7cc35dbeb9b18a5cbac
• https://git.kernel.org/stable/c/eb592008f79be52ccef88cd9a5249b3fc0367278