net: possible use after free in dst_release

dst_release should not access dst->flags after decrementing
__refcnt to 0. The dst_entry may be in dst_busy_list and
dst_gc_task may dst_destroy it before dst_release gets a chance
to access dst->flags.

Fixes: d69bbf88c8d0 ("net: fix a race in dst_release()")
Fixes: 27b75c95f10d ("net: avoid RCU for NOCACHE dst")
Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dst.c b/net/core/dst.c
index e6dc77252fe9fa3e401529426079f094c9f6f999..a1656e3b8d72a66ff56656284205129ecfd30b3e 100644 (file)
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -301,12 +301,13 @@ void dst_release(struct dst_entry *dst)
 {
        if (dst) {
                int newrefcnt;
+               unsigned short nocache = dst->flags & DST_NOCACHE;
 
                newrefcnt = atomic_dec_return(&dst->__refcnt);
                if (unlikely(newrefcnt < 0))
                        net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
                                             __func__, dst, newrefcnt);
-               if (!newrefcnt && unlikely(dst->flags & DST_NOCACHE))
+               if (!newrefcnt && unlikely(nocache))
                        call_rcu(&dst->rcu_head, dst_destroy_rcu);
        }
 }