Re: [Xen-devel] kernel panic in skb_copy_bits

[Eric Dumazet <eric.dumazet@xxxxxxxxx>]

OK please try the following patch


[PATCH] neighbour: fix a race in neigh_destroy()

There is a race in neighbour code, because neigh_destroy() uses
skb_queue_purge(&neigh->arp_queue) without holding neighbour lock,
while other parts of the code assume neighbour rwlock is what
protects arp_queue

Convert all skb_queue_purge() calls to the __skb_queue_purge() variant

Use __skb_queue_head_init() instead of skb_queue_head_init()
to make clear we do not use arp_queue.lock

And hold neigh->lock in neigh_destroy() to close the race.

Reported-by: Joe Jin <joe.jin@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
---
 net/core/neighbour.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 2569ab2..b7de821 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -231,7 +231,7 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct 
net_device *dev)
                                   we must kill timers etc. and move
                                   it to safe state.
                                 */
-                               skb_queue_purge(&n->arp_queue);
+                               __skb_queue_purge(&n->arp_queue);
                                n->arp_queue_len_bytes = 0;
                                n->output = neigh_blackhole;
                                if (n->nud_state & NUD_VALID)
@@ -286,7 +286,7 @@ static struct neighbour *neigh_alloc(struct neigh_table 
*tbl, struct net_device
        if (!n)
                goto out_entries;
 
-       skb_queue_head_init(&n->arp_queue);
+       __skb_queue_head_init(&n->arp_queue);
        rwlock_init(&n->lock);
        seqlock_init(&n->ha_lock);
        n->updated        = n->used = now;
@@ -708,7 +708,9 @@ void neigh_destroy(struct neighbour *neigh)
        if (neigh_del_timer(neigh))
                pr_warn("Impossible event\n");
 
-       skb_queue_purge(&neigh->arp_queue);
+       write_lock_bh(&neigh->lock);
+       __skb_queue_purge(&neigh->arp_queue);
+       write_unlock_bh(&neigh->lock);
        neigh->arp_queue_len_bytes = 0;
 
        if (dev->netdev_ops->ndo_neigh_destroy)
@@ -858,7 +860,7 @@ static void neigh_invalidate(struct neighbour *neigh)
                neigh->ops->error_report(neigh, skb);
                write_lock(&neigh->lock);
        }
-       skb_queue_purge(&neigh->arp_queue);
+       __skb_queue_purge(&neigh->arp_queue);
        neigh->arp_queue_len_bytes = 0;
 }
 
@@ -1210,7 +1212,7 @@ int neigh_update(struct neighbour *neigh, const u8 
*lladdr, u8 new,
 
                        write_lock_bh(&neigh->lock);
                }
-               skb_queue_purge(&neigh->arp_queue);
+               __skb_queue_purge(&neigh->arp_queue);
                neigh->arp_queue_len_bytes = 0;
        }
 out:



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