[RFC] ethdev: fix UAF in rte_eth_tx_burst with filtering

[Stephen Hemminger <stephen@networkplumber.org>]

When packets are filtered by Tx callback, they return value
needs to include those packets; otherwise the application will
do a duplicate free of those mbufs.

The example would be application that sent a burst of 8 packets,
and 2 were filtered but the PMD was busy and could not send any.
The result should be a return value of 2 and mbufs 0..1 should
be freed and 2..7 should be untouched and up to application to
resend or drop.

Original buggy code would return 0 and 0..1 would be freed
2..7 would be unused. Application would then try and drop
or resend an already freed mbuf.

Bugzilla ID: 1816
Fixes: 4dc294158cac ("ethdev: support optional Rx and Tx callbacks")
Cc: bruce.richardson@intel.com
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/ethdev/rte_ethdev.h | 47 ++++++++++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 12 deletions(-)

diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
index a66c2abbdb..d2cfe390f9 100644
--- a/lib/ethdev/rte_ethdev.h
+++ b/lib/ethdev/rte_ethdev.h
@@ -6714,6 +6714,10 @@ rte_eth_tx_burst(uint16_t port_id, uint16_t queue_id,
 	}
 #endif
 
+	uint16_t requested_pkts = nb_pkts;
+	uint16_t filtered_pkts = 0;
+	rte_mbuf_history_mark_bulk(tx_pkts, nb_pkts, RTE_MBUF_HISTORY_OP_TX);
+
 #ifdef RTE_ETHDEV_RXTX_CALLBACKS
 	{
 		void *cb;
@@ -6727,22 +6731,41 @@ rte_eth_tx_burst(uint16_t port_id, uint16_t queue_id,
 		cb = rte_atomic_load_explicit(&p->txq.clbk[queue_id],
 				rte_memory_order_relaxed);
 		if (unlikely(cb != NULL))
-			nb_pkts = rte_eth_call_tx_callbacks(port_id, queue_id,
-					tx_pkts, nb_pkts, cb);
+			filtered_pkts = nb_pkts -
+				rte_eth_call_tx_callbacks(port_id, queue_id, tx_pkts, nb_pkts, cb);
 	}
 #endif
 
-	uint16_t requested_pkts = nb_pkts;
-	rte_mbuf_history_mark_bulk(tx_pkts, nb_pkts, RTE_MBUF_HISTORY_OP_TX);
-
-	nb_pkts = p->tx_pkt_burst(qd, tx_pkts, nb_pkts);
-
-	if (requested_pkts > nb_pkts)
-		rte_mbuf_history_mark_bulk(tx_pkts + nb_pkts,
-				requested_pkts - nb_pkts, RTE_MBUF_HISTORY_OP_TX_BUSY);
+	uint16_t sent_pkts = p->tx_pkt_burst(qd, tx_pkts, nb_pkts - filtered_pkts);
+	uint16_t result_pkts = sent_pkts + filtered_pkts;
+
+	if (unlikely(result_pkts < requested_pkts)) {
+		uint16_t unsent_pkts = requested_pkts - result_pkts;
+
+		if (unlikely(filtered_pkts > 0)) {
+			/* Need to reshuffle packet list so that unsent packets are
+			 * after the return value
+			 *
+			 * Original: MMMMMM
+			 * Filter:   MMMMMF filtered = 1
+			 * Tx_burst: SSSUUF sent = 3 unsent = 2
+			 *
+			 * Return:   SSSFUU
+			 *   return from tx_burst is 4
+			 */
+			memmove(tx_pkts + result_pkts, tx_pkts + sent_pkts,
+				unsent_pkts * sizeof(struct rte_mbuf *));
+
+			/* Tx filter process does not drop the packets until here */
+			rte_pktmbuf_free_bulk(tx_pkts + sent_pkts, filtered_pkts);
+		}
+
+		rte_mbuf_history_mark_bulk(tx_pkts + result_pkts, unsent_pkts,
+					   RTE_MBUF_HISTORY_OP_TX_BUSY);
+	}
 
-	rte_ethdev_trace_tx_burst(port_id, queue_id, (void **)tx_pkts, nb_pkts);
-	return nb_pkts;
+	rte_ethdev_trace_tx_burst(port_id, queue_id, (void **)tx_pkts, result_pkts);
+	return result_pkts;
 }
 
 /**
-- 
2.51.0