[PATCH 4.14 15/57] net-sysfs: take the rtnl lock when storing xps_cpus

Greg Kroah-Hartman
2021-01-11T14:00:12Z

From: Antoine Tenart <atenart@kernel.org>

[ Upstream commit 1ad58225dba3f2f598d2c6daed4323f24547168f ]

Two race conditions can be triggered when storing xps cpus, resulting in
various oops and invalid memory accesses:

1. Calling netdev_set_num_tc while netif_set_xps_queue:

- 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.

2. Calling netif_set_xps_queue while netdev_set_num_tc is running:

2.1. netdev_set_num_tc starts by resetting the xps queues,
dev->tc_num isn't updated yet.

2.2. netif_set_xps_queue is called, setting up the map with the
*old* dev->num_tc.

2.3. netdev_set_num_tc updates dev->tc_num.

2.4. Later accesses to the map lead to out of bound accesses and
oops.

A similar issue can be found with netdev_reset_tc.

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.

Both issues have the same fix: netif_set_xps_queue, netdev_set_num_tc
and netdev_reset_tc should be mutually exclusive. We do that by taking
the rtnl lock in xps_cpus_store.

Fixes: 184c449f91fe ("net: Add support for XPS with QoS via traffic classes")
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/net-sysfs.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1273,7 +1273,13 @@ static ssize_t xps_cpus_store(struct net
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);