netdev - [PATCH 2/6 net-next] net/l2tp: Add missing sa_family validation in pppol2tp_sockaddr_get

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Message-Id: <20250723231921.2293685-2-kees@kernel.org>
Date: Wed, 23 Jul 2025 16:19:09 -0700
From: Kees Cook <kees@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Kees Cook <kees@...nel.org>,
	James Chapman <jchapman@...alix.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	netdev@...r.kernel.org,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH 2/6 net-next] net/l2tp: Add missing sa_family validation in pppol2tp_sockaddr_get_info

While reviewing the struct proto_ops connect() and bind() callback
implementations, I noticed that there doesn't appear to be any
validation that AF_PPPOX sockaddr structures actually have sa_family set
to AF_PPPOX. The pppol2tp_sockaddr_get_info() checks only look at the
sizes.

I don't see any way that this might actually cause problems as specific
info fields are being populated, for which the existing size checks are
correct, but it stood out as a missing address family check.

Add the check and return -EAFNOSUPPORT on mismatch.

Signed-off-by: Kees Cook <kees@...nel.org>
---
Cc: James Chapman <jchapman@...alix.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>
Cc: <netdev@...r.kernel.org>
---
 net/l2tp/l2tp_ppp.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index fc5c2fd8f34c..767b393cbb78 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -545,6 +545,13 @@ struct l2tp_connect_info {
 static int pppol2tp_sockaddr_get_info(const void *sa, int sa_len,
 				      struct l2tp_connect_info *info)
 {
+	const struct sockaddr_unspec *sockaddr = sa;
+
+	if (sa_len < offsetofend(struct sockaddr, sa_family))
+		return -EINVAL;
+	if (sockaddr->sa_family != AF_PPPOX)
+		return -EAFNOSUPPORT;
+
 	switch (sa_len) {
 	case sizeof(struct sockaddr_pppol2tp):
 	{
-- 
2.34.1