[PATCH net 6/9] netfilter: nft_tunnel: fix use-after-free on object destroy

[Pablo Neira Ayuso <pablo@netfilter.org>]

From: Tristan Madani <tristan@talencesecurity.com>

nft_tunnel_obj_destroy() calls metadata_dst_free() which directly
kfree()s the metadata_dst, ignoring the dst_entry refcount. Packets
that took a reference via dst_hold() in nft_tunnel_obj_eval() and
are still queued (e.g. in a netem qdisc) are left with a dangling
pointer. When these packets are eventually dequeued, dst_release()
operates on freed memory.

Replace metadata_dst_free() with dst_release() so the metadata_dst
is freed only after all references are dropped. The dst subsystem
already handles metadata_dst cleanup in dst_destroy() when
DST_METADATA is set.

Fixes: af308b94a2a4 ("netfilter: nf_tables: add tunnel support")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nft_tunnel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nft_tunnel.c b/net/netfilter/nft_tunnel.c
index 0b987bc2132a..68f7cfbbee06 100644
--- a/net/netfilter/nft_tunnel.c
+++ b/net/netfilter/nft_tunnel.c
@@ -676,7 +676,7 @@ static void nft_tunnel_obj_destroy(const struct nft_ctx *ctx,
 {
 	struct nft_tunnel_obj *priv = nft_obj_data(obj);
 
-	metadata_dst_free(priv->md);
+	dst_release(&priv->md->dst);
 }
 
 static struct nft_object_type nft_tunnel_obj_type;
-- 
2.47.3