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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Antoine Tenart <atenart@kernel.org>,
        Alexander Duyck <alexanderduyck@fb.com>,
        Jakub Kicinski <kuba@kernel.org>
Subject: [PATCH 5.4 28/92] net-sysfs: take the rtnl lock when storing xps_rxqs
Date:   Mon, 11 Jan 2021 14:01:32 +0100
Message-Id: <20210111130040.500605721@linuxfoundation.org>
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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
@@ -1417,10 +1417,17 @@ 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();
+
 	bitmap_free(mask);
 	return err ? : len;
 }