liquidio: Adjust a NULL pointer handling path in lio_vf_rep_copy_packet

In the Linux kernel, the following vulnerability has been resolved:

liquidio: Adjust a NULL pointer handling path in lio_vf_rep_copy_packet

In lio_vf_rep_copy_packet() pg_info->page is compared to a NULL value,

but then it is unconditionally passed to skb_add_rx_frag() which looks

strange and could lead to null pointer dereference.

lio_vf_rep_copy_packet() call trace looks like:

octeon_droq_process_packets

octeon_droq_fast_process_packets

octeon_droq_dispatch_pkt

octeon_create_recv_info

...search in the dispatch_list...

->disp_fn(rdisp->rinfo, ...)

lio_vf_rep_pkt_recv(struct octeon_recv_info *recv_info, ...)

In this path there is no code which sets pg_info->page to NULL.

So this check looks unneeded and doesn't solve potential problem.

But I guess the author had reason to add a check and I have no such card

and can't do real test.

In addition, the code in the function liquidio_push_packet() in

liquidio/lio_core.c does exactly the same.

Based on this, I consider the most acceptable compromise solution to

adjust this issue by moving skb_add_rx_frag() into conditional scope.

Found by Linux Verification Center (linuxtesting.org) with SVACE.