[PATCH] ipv6: udp: fix memory leak in udpv6_sendmsg error path

[Mingyu Wang]

During fuzzing with failslab enabled, a memory leak was observed in the
IPv6 UDP send path.

When sending via the lockless fast path (!corkreq), udpv6_sendmsg()
calls ip6_make_skb() and assumes that the routing entry (dst_entry)
reference has been stolen by the callee. However, if ip6_make_skb()
fails early (e.g., due to an ENOMEM from memory allocation failure),
it returns an error pointer without consuming the dst reference.

Since udpv6_sendmsg() unconditionally jumps to the 'out_no_dst' label,
the unconsumed dst_entry is never released, resulting in a memory leak.

Fix this by explicitly calling dst_release(dst) when ip6_make_skb()
returns an error.

Signed-off-by: Mingyu Wang <25181214217@xxxxxxxxxxxxxxxxx>
---
 net/ipv6/udp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 15e032194ecc..b83ecfd729af 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1706,8 +1706,11 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 				   dst_rt6_info(dst),
 				   msg->msg_flags, &cork);
 		err = PTR_ERR(skb);
-		if (!IS_ERR_OR_NULL(skb))
+		if (!IS_ERR_OR_NULL(skb)) {
 			err = udp_v6_send_skb(skb, fl6, &cork.base);
+		} else {
+			dst_release(dst);
+		}
 		/* ip6_make_skb steals dst reference */
 		goto out_no_dst;
 	}
-- 
2.34.1