From: Florian Westphal <fw@strlen.de>
Date: Thu, 21 Nov 2019 06:56:23 +0100
Subject: udp: drop skb extensions before marking skb stateless
Patch-mainline: v5.4
Git-commit: 677bf08cfdf9ee411c2084157f15d85edb09a81a
References: bsc#1176447

Once udp stack has set the UDP_SKB_IS_STATELESS flag, later skb free
assumes all skb head state has been dropped already.

This will leak the extension memory in case the skb has extensions other
than the ipsec secpath, e.g. bridge nf data.

To fix this, set the UDP_SKB_IS_STATELESS flag only if we don't have
extensions or if the extension space can be free'd.

Fixes: 895b5c9f206eb7d25dc1360a ("netfilter: drop bridge nf reset from nf_reset")
Cc: Paolo Abeni <pabeni@redhat.com>
Reported-by: Byron Stanoszek <gandalf@winds.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 include/linux/skbuff.h |    6 ++++++
 net/ipv4/udp.c         |   27 ++++++++++++++++++++++-----
 2 files changed, 28 insertions(+), 5 deletions(-)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4169,12 +4169,18 @@ static inline void skb_ext_reset(struct
 		skb->active_extensions = 0;
 	}
 }
+
+static inline bool skb_has_extensions(struct sk_buff *skb)
+{
+	return unlikely(skb->active_extensions);
+}
 #else
 static inline void skb_ext_put(struct sk_buff *skb) {}
 static inline void skb_ext_reset(struct sk_buff *skb) {}
 static inline void skb_ext_del(struct sk_buff *skb, int unused) {}
 static inline void __skb_ext_copy(struct sk_buff *d, const struct sk_buff *s) {}
 static inline void skb_ext_copy(struct sk_buff *dst, const struct sk_buff *s) {}
+static inline bool skb_has_extensions(struct sk_buff *skb) { return false; }
 #endif /* CONFIG_SKB_EXTENSIONS */
 
 static inline void nf_reset_ct(struct sk_buff *skb)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1297,6 +1297,27 @@ out:
 
 #define UDP_SKB_IS_STATELESS 0x80000000
 
+/* all head states (dst, sk, nf conntrack) except skb extensions are
+ * cleared by udp_rcv().
+ *
+ * We need to preserve secpath, if present, to eventually process
+ * IP_CMSG_PASSSEC at recvmsg() time.
+ *
+ * Other extensions can be cleared.
+ */
+static bool udp_try_make_stateless(struct sk_buff *skb)
+{
+	if (!skb_has_extensions(skb))
+		return true;
+
+	if (!secpath_exists(skb)) {
+		skb_ext_reset(skb);
+		return true;
+	}
+
+	return false;
+}
+
 static void udp_set_dev_scratch(struct sk_buff *skb)
 {
 	struct udp_dev_scratch *scratch = udp_skb_scratch(skb);
@@ -1308,11 +1329,7 @@ static void udp_set_dev_scratch(struct s
 	scratch->csum_unnecessary = !!skb_csum_unnecessary(skb);
 	scratch->is_linear = !skb_is_nonlinear(skb);
 #endif
-	/* all head states execept sp (dst, sk, nf) are always cleared by
-	 * udp_rcv() and we need to preserve secpath, if present, to eventually
-	 * process IP_CMSG_PASSSEC at recvmsg() time
-	 */
-	if (likely(!skb_sec_path(skb)))
+	if (udp_try_make_stateless(skb))
 		scratch->_tsize_state |= UDP_SKB_IS_STATELESS;
 }