From: Chinmay Agarwal chinagar@codeaurora.org
commit eefb45eef5c4c425e87667af8f5e904fbdd47abf upstream.
Following Race Condition was detected:
<CPU A, t0>: Executing: __netif_receive_skb() ->__netif_receive_skb_core() -> arp_rcv() -> arp_process().arp_process() calls __neigh_lookup() which takes a reference on neighbour entry 'n'. Moves further along, arp_process() and calls neigh_update()-> __neigh_update(). Neighbour entry is unlocked just before a call to neigh_update_gc_list.
This unlocking paves way for another thread that may take a reference on the same and mark it dead and remove it from gc_list.
<CPU B, t1> - neigh_flush_dev() is under execution and calls neigh_mark_dead(n) marking the neighbour entry 'n' as dead. Also n will be removed from gc_list. Moves further along neigh_flush_dev() and calls neigh_cleanup_and_release(n), but since reference count increased in t1, 'n' couldn't be destroyed.
<CPU A, t3>- Code hits neigh_update_gc_list, with neighbour entry set as dead.
<CPU A, t4> - arp_process() finally calls neigh_release(n), destroying the neighbour entry and we have a destroyed ntry still part of gc_list.
Fixes: eb4e8fac00d1("neighbour: Prevent a dead entry from updating gc_list") Signed-off-by: Chinmay Agarwal chinagar@codeaurora.org Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/neighbour.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -131,6 +131,9 @@ static void neigh_update_gc_list(struct write_lock_bh(&n->tbl->lock); write_lock(&n->lock);
+ if (n->dead) + goto out; + /* remove from the gc list if new state is permanent or if neighbor * is externally learned; otherwise entry should be on the gc list */ @@ -147,6 +150,7 @@ static void neigh_update_gc_list(struct atomic_inc(&n->tbl->gc_entries); }
+out: write_unlock(&n->lock); write_unlock_bh(&n->tbl->lock); }