[PATCH net v3] liquidio: Adjust a NULL pointer handling path in lio_vf_rep_copy_packet

[Aleksandr Mishin]

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.

Fixes: 1f233f327913 ("liquidio: switchdev support for LiquidIO NIC")
Signed-off-by: Aleksandr Mishin <amishin@xxxxxxxxxx>
Reviewed-by: Simon Horman <horms@xxxxxxxxxx>
---
v1->v2: Fix incorrect 'Fixes' tag format
v2->v3: Add explanation why this should be fixed,
 add Reviewed-by: Simon Horman <horms@xxxxxxxxxx>
 (https://lore.kernel.org/all/20240308201911.GB603911@xxxxxxxxxx/)

 drivers/net/ethernet/cavium/liquidio/lio_vf_rep.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/cavium/liquidio/lio_vf_rep.c b/drivers/net/ethernet/cavium/liquidio/lio_vf_rep.c
index aa6c0dfb6f1c..e26b4ed33dc8 100644
--- a/drivers/net/ethernet/cavium/liquidio/lio_vf_rep.c
+++ b/drivers/net/ethernet/cavium/liquidio/lio_vf_rep.c
@@ -272,13 +272,12 @@ lio_vf_rep_copy_packet(struct octeon_device *oct,
 				pg_info->page_offset;
 			memcpy(skb->data, va, MIN_SKB_SIZE);
 			skb_put(skb, MIN_SKB_SIZE);
+			skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
+					pg_info->page,
+					pg_info->page_offset + MIN_SKB_SIZE,
+					len - MIN_SKB_SIZE,
+					LIO_RXBUFFER_SZ);
 		}
-
-		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
-				pg_info->page,
-				pg_info->page_offset + MIN_SKB_SIZE,
-				len - MIN_SKB_SIZE,
-				LIO_RXBUFFER_SZ);
 	} else {
 		struct octeon_skb_page_info *pg_info =
 			((struct octeon_skb_page_info *)(skb->cb));
-- 
2.30.2