[PATCH net v1 1/2] net/mlx5e: RX, Fix generating skb from non-linear xdp_buff for legacy RQ

[Amery Hung <ameryhung@gmail.com>]

XDP programs can release xdp_buff fragments when calling
bpf_xdp_adjust_tail(). The driver currently assumes the number of
fragments to be unchanged and may generate skb with wrong truesize or
containing invalid frags. Fix the bug by generating skb according to
xdp_buff after the XDP program runs.

Fixes: ea5d49bdae8b ("net/mlx5e: Add XDP multi buffer support to the non-linear legacy RQ")
Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index b8c609d91d11..1d3eacfd0325 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -1729,6 +1729,7 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5e_wqe_frag_info *wi
 	struct mlx5e_wqe_frag_info *head_wi = wi;
 	u16 rx_headroom = rq->buff.headroom;
 	struct mlx5e_frag_page *frag_page;
+	u8 nr_frags_free, old_nr_frags;
 	struct skb_shared_info *sinfo;
 	u32 frag_consumed_bytes;
 	struct bpf_prog *prog;
@@ -1772,17 +1773,25 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5e_wqe_frag_info *wi
 		wi++;
 	}
 
+	old_nr_frags = sinfo->nr_frags;
+
 	prog = rcu_dereference(rq->xdp_prog);
 	if (prog && mlx5e_xdp_handle(rq, prog, mxbuf)) {
 		if (__test_and_clear_bit(MLX5E_RQ_FLAG_XDP_XMIT, rq->flags)) {
 			struct mlx5e_wqe_frag_info *pwi;
 
+			wi -= old_nr_frags - sinfo->nr_frags;
+
 			for (pwi = head_wi; pwi < wi; pwi++)
 				pwi->frag_page->frags++;
 		}
 		return NULL; /* page/packet was consumed by XDP */
 	}
 
+	nr_frags_free = old_nr_frags - sinfo->nr_frags;
+	wi -= nr_frags_free;
+	truesize -= nr_frags_free * frag_info->frag_stride;
+
 	skb = mlx5e_build_linear_skb(
 		rq, mxbuf->xdp.data_hard_start, rq->buff.frame0_sz,
 		mxbuf->xdp.data - mxbuf->xdp.data_hard_start,
-- 
2.47.3