net: possible use after free in dst_release

[ Upstream commit 07a5d38453599052aff0877b16bb9c1585f08609 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/core/dst.c b/net/core/dst.c
index f8db403..540066c 100644 (file)
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -282,10 +282,11 @@ void dst_release(struct dst_entry *dst)
 {
        if (dst) {
                int newrefcnt;
+               unsigned short nocache = dst->flags & DST_NOCACHE;
 
                newrefcnt = atomic_dec_return(&dst->__refcnt);
                WARN_ON(newrefcnt < 0);
-               if (!newrefcnt && unlikely(dst->flags & DST_NOCACHE))
+               if (!newrefcnt && unlikely(nocache))
                        call_rcu(&dst->rcu_head, dst_destroy_rcu);
        }
 }