[PATCH] Fix dst_destroy() race

When we are not the real parent of the dst (e.g., when we're xfrm_dst and
the child is an rtentry), it may already be on the GC list.

In fact the current code is buggy to, we need to check dst->flags before
the dec as dst may no longer be valid afterwards.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/net/core/dst.c b/net/core/dst.c
index 3bf6cc4..fc434ad 100644 (file)
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -198,13 +198,15 @@ again:
 
        dst = child;
        if (dst) {
+               int nohash = dst->flags & DST_NOHASH;
+
                if (atomic_dec_and_test(&dst->__refcnt)) {
                        /* We were real parent of this dst, so kill child. */
-                       if (dst->flags&DST_NOHASH)
+                       if (nohash)
                                goto again;
                } else {
                        /* Child is still referenced, return it for freeing. */
-                       if (dst->flags&DST_NOHASH)
+                       if (nohash)
                                return dst;
                        /* Child is still in his hash table */
                }