[PATCH 5/9] net/gve: set mbuf to null in software ring after use

[Joshua Washington <joshwash@google.com>]

Currently, it is possible for mbufs to be uncleared in the sw_ring after
being returned to the application. This causes an erroneous
dual-ownership over the buffer until GVE cleans the buffer queue and
posts new mbufs, overwriting the older pointers. It is possible in such
a case for a double free to occur while tearing down rings, as both
the application and the driver could attempt to free the same mbuf.
Release ownership of the mbuf from the sw_ring as soon as appropriate to
avoid such a scenario.

Fixes: a46583cf43c8 ("net/gve: support Rx/Tx")
Fixes: 45da16b5b181 ("net/gve: support basic Rx data path for DQO")
Cc: stable@dpdk.org
Signed-off-by: Joshua Washington <joshwash@google.com>
Reviewed-by: Jasper Tran O'Leary <jtranoleary@google.com>
---
 drivers/net/gve/gve_rx.c     | 1 +
 drivers/net/gve/gve_rx_dqo.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/drivers/net/gve/gve_rx.c b/drivers/net/gve/gve_rx.c
index 625649cdcf..cda87af294 100644
--- a/drivers/net/gve/gve_rx.c
+++ b/drivers/net/gve/gve_rx.c
@@ -152,6 +152,7 @@ gve_rx(struct gve_rx_queue *rxq, volatile struct gve_rx_desc *rxd, uint16_t rx_i

 	rxe = rxq->sw_ring[rx_id];
 	gve_rx_mbuf(rxq, rxe, frag_size, rx_id);
+	rxq->sw_ring[rx_id] = NULL;
 	rxq->stats.bytes += frag_size;

 	if (is_first_frag) {
diff --git a/drivers/net/gve/gve_rx_dqo.c b/drivers/net/gve/gve_rx_dqo.c
index c4e2d32067..3665d9e4cd 100644
--- a/drivers/net/gve/gve_rx_dqo.c
+++ b/drivers/net/gve/gve_rx_dqo.c
@@ -207,6 +207,7 @@ gve_rx_burst_dqo(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts)

 		rxm = rxq->sw_ring[rx_buf_id];
 		gve_completed_buf_list_push(rxq, rx_buf_id);
+		rxq->sw_ring[rx_buf_id] = NULL;

 		/* Free buffer and report error. */
 		if (unlikely(rx_desc->rx_error)) {
--
2.55.0.rc0.799.gd6f94ed593-goog