Callers to netif_set_xps_queue should take the rtnl lock. Failing to do
so can lead to race conditions between netdev_set_num_tc and
netif_set_xps_queue, triggering various oops:
- netif_set_xps_queue uses dev->tc_num as one of the parameters to
compute the size of new_dev_maps when allocating it. dev->tc_num is
also used to access the map, and the compiler may generate code to
retrieve this field multiple times in the function.
- netdev_set_num_tc sets dev->tc_num.
If new_dev_maps is allocated using dev->tc_num and then dev->tc_num is
set to a higher value through netdev_set_num_tc, later accesses to
new_dev_maps in netif_set_xps_queue could lead to accessing memory
outside of new_dev_maps; triggering an oops.
One way of triggering this is to set an iface up (for which the driver
uses netdev_set_num_tc in the open path, such as bnx2x) and writing to
xps_cpus in a concurrent thread. With the right timing an oops is
triggered.
Fixes: 184c449f91fe ("net: Add support for XPS with QoS via traffic classes")
Signed-off-by: Antoine Tenart <aten...@kernel.org>
---
net/core/net-sysfs.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 999b70c59761..7cc15dec1717 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1396,7 +1396,13 @@ static ssize_t xps_cpus_store(struct netdev_queue *queue,
return err;
}
+ if (!rtnl_trylock()) {
+ free_cpumask_var(mask);
+ return restart_syscall();
+ }
+
err = netif_set_xps_queue(dev, mask, index);
+ rtnl_unlock();
free_cpumask_var(mask);
--
2.29.2
