net: fix use after free in xps

When setting up an new dev_maps in __netif_set_xps_queue, we remove and
free maps from unused CPUs/rx-queues near the end of the function; by
calling remove_xps_queue. However it's possible those maps are also part
of the old not-freed-yet dev_maps, which might be used concurrently.
When that happens, a map can be freed while its corresponding entry in
the old dev_maps table isn't NULLed, leading to: "BUG: KASAN:
use-after-free" in different places.

This fixes the map freeing logic for unused CPUs/rx-queues, to also NULL
the map entries from the old dev_maps table.

Signed-off-by: Antoine Tenart <atenart@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index c8ce2df..d5f6ba2 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2460,7 +2460,7 @@ static DEFINE_MUTEX(xps_map_mutex);
        rcu_dereference_protected((P), lockdep_is_held(&xps_map_mutex))
 
 static bool remove_xps_queue(struct xps_dev_maps *dev_maps,
-                            int tci, u16 index)
+                            struct xps_dev_maps *old_maps, int tci, u16 index)
 {
        struct xps_map *map = NULL;
        int pos;
@@ -2479,6 +2479,8 @@ static bool remove_xps_queue(struct xps_dev_maps *dev_maps,
                        break;
                }
 
+               if (old_maps)
+                       RCU_INIT_POINTER(old_maps->attr_map[tci], NULL);
                RCU_INIT_POINTER(dev_maps->attr_map[tci], NULL);
                kfree_rcu(map, rcu);
                return false;
@@ -2499,7 +2501,7 @@ static bool remove_xps_queue_cpu(struct net_device *dev,
                int i, j;
 
                for (i = count, j = offset; i--; j++) {
-                       if (!remove_xps_queue(dev_maps, tci, j))
+                       if (!remove_xps_queue(dev_maps, NULL, tci, j))
                                break;
                }
 
@@ -2631,7 +2633,7 @@ static void xps_copy_dev_maps(struct xps_dev_maps *dev_maps,
 int __netif_set_xps_queue(struct net_device *dev, const unsigned long *mask,
                          u16 index, enum xps_map_type type)
 {
-       struct xps_dev_maps *dev_maps, *new_dev_maps = NULL;
+       struct xps_dev_maps *dev_maps, *new_dev_maps = NULL, *old_dev_maps = NULL;
        const unsigned long *online_mask = NULL;
        bool active = false, copy = false;
        int i, j, tci, numa_node_id = -2;
@@ -2766,7 +2768,7 @@ int __netif_set_xps_queue(struct net_device *dev, const unsigned long *mask,
                }
        }
 
-       kfree_rcu(dev_maps, rcu);
+       old_dev_maps = dev_maps;
 
 out_no_old_maps:
        dev_maps = new_dev_maps;
@@ -2792,10 +2794,15 @@ out_no_new_maps:
                            netif_attr_test_online(j, online_mask, dev_maps->nr_ids))
                                continue;
 
-                       active |= remove_xps_queue(dev_maps, tci, index);
+                       active |= remove_xps_queue(dev_maps,
+                                                  copy ? old_dev_maps : NULL,
+                                                  tci, index);
                }
        }
 
+       if (old_dev_maps)
+               kfree_rcu(old_dev_maps, rcu);
+
        /* free map if not active */
        if (!active)
                reset_xps_maps(dev, dev_maps, type);