From 5c7b23b7962865766147c5d7dc3f6e15b96dbe18 Mon Sep 17 00:00:00 2001 From: Chinmay Agarwal Date: Thu, 22 Apr 2021 01:12:22 +0530 Subject: [PATCH] neighbour: Prevent Race condition in neighbour subsytem commit eefb45eef5c4c425e87667af8f5e904fbdd47abf upstream. Following Race Condition was detected: : 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. - 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. - Code hits neigh_update_gc_list, with neighbour entry set as dead. - 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 Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/core/neighbour.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/core/neighbour.c b/net/core/neighbour.c index 8339978d46ff8..a18c2973b8c6d 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -132,6 +132,9 @@ static void neigh_update_gc_list(struct neighbour *n) 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 */ @@ -148,6 +151,7 @@ static void neigh_update_gc_list(struct neighbour *n) atomic_inc(&n->tbl->gc_entries); } +out: write_unlock(&n->lock); write_unlock_bh(&n->tbl->lock); }