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 could
lead to null pointer dereference.
Fix this bug 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@t-argos.ru>
---
v2: Fix incorrect 'Fixes' tag format

 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

On Fri, 22 Mar 2024 22:57:44 +0300 Aleksandr Mishin wrote:
> 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 could
> lead to null pointer dereference.
> Fix this bug by moving skb_add_rx_frag() into conditional scope.

The explanation should tell us how the bug can happen, i.e. what
sequence of events leads to null-deref. Not what logic your tool
matched on, perhaps the NULL check is unnecessary.
-- 
pw-bot: cr