[dpdk-stable] [PATCH 2/2] net/bonding: avoid the next active slave going out of bound

[Hyong Youb Kim]

For bonding modes like broadcast that use bond_ethdev_rx_burst(), it
is fairly easy to produce a crash simply by bringing a slave port's
link down. When slave links go down, the driver on one thread reduces
active_slave_count via the LSC callback and deactivate_slave(). At the
same time, bond_ethdev_rx_burst() running on a forwarding thread may
increment active_slave (next active slave) beyond
active_slave_count. Here is a typical sequence of events.

At time 0:
active_slave_count = 3
active_slave = 2

At time 1:
A slave link goes down.
Thread 0 (main) reduces active_slave_count to 2.

At time 2:
Thread 1 (forwarding) executes bond_ethdev_rx_burst().
- Reads active_slave_count = 2.
- Increments active_slave at the end to 3.

>From this point on, everytime bond_ethdev_rx_burst() runs,
active_slave increments by one, eventually going well out of bound of
the active_slaves array and causing a crash.

Make the rx burst function to first check that active_slave is within
bound. If not, reset it to 0 to avoid out-of-range array access.

Fixes: e1110e977648 ("net/bonding: fix Rx slave fairness")
Cc: stable at dpdk.org

Signed-off-by: Hyong Youb Kim <hyonkim at cisco.com>
---
 drivers/net/bonding/rte_eth_bond_pmd.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/net/bonding/rte_eth_bond_pmd.c b/drivers/net/bonding/rte_eth_bond_pmd.c
index daf2440cd..bc2405e54 100644
--- a/drivers/net/bonding/rte_eth_bond_pmd.c
+++ b/drivers/net/bonding/rte_eth_bond_pmd.c
@@ -68,6 +68,15 @@ bond_ethdev_rx_burst(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 	internals = bd_rx_q->dev_private;
 	slave_count = internals->active_slave_count;
 	active_slave = internals->active_slave;
+	/*
+	 * Reset the active slave index, in case active_slave goes out
+	 * of bound.  It can hapen when slave links go down, and
+	 * another thread (LSC callback) shrinks the slave count.
+	 */
+	if (active_slave >= slave_count) {
+		internals->active_slave = 0;
+		active_slave = 0;
+	}
 
 	for (i = 0; i < slave_count && nb_pkts; i++) {
 		uint16_t num_rx_slave;
@@ -273,6 +282,11 @@ bond_ethdev_rx_burst_8023ad_fast_queue(void *queue, struct rte_mbuf **bufs,
 	active_slave = internals->active_slave;
 	memcpy(slaves, internals->active_slaves,
 			sizeof(internals->active_slaves[0]) * slave_count);
+	/* active_slave may go out of bound. See bond_ethdev_rx_burst() */
+	if (active_slave >= slave_count) {
+		internals->active_slave = 0;
+		active_slave = 0;
+	}
 
 	for (i = 0; i < slave_count && nb_pkts; i++) {
 		uint16_t num_rx_slave;
-- 
2.16.2