[PATCH 4.19 36/77] net-sysfs: take the rtnl lock when storing xps_rxqs

Greg Kroah-Hartman
2021-01-11T13:53:56Z

From: Antoine Tenart <atenart@kernel.org>

[ Upstream commit 2d57b4f142e0b03e854612b8e28978935414bced ]

Two race conditions can be triggered when storing xps rxqs, 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_rxqs 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_rxqs_store.

Fixes: 8af2c06ff4b1 ("net-sysfs: Add interface for Rx queue(s) map per Tx queue")
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 | 7 +++++++
1 file changed, 7 insertions(+)

--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1428,10 +1428,17 @@ static ssize_t xps_rxqs_store(struct net
return err;
}

+ if (!rtnl_trylock()) {
+ bitmap_free(mask);
+ return restart_syscall();
+ }
+
cpus_read_lock();
err = __netif_set_xps_queue(dev, mask, index, true);
cpus_read_unlock();

+ rtnl_unlock();
+
kfree(mask);
return err ? : len;
}