[PATCH v3 2/9] net/l2tp: Add missing sa_family validation in pppol2tp_sockaddr_get_info

[Kees Cook <kees@kernel.org>]

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@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 5e12e7ce17d8..b7a9c224520f 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -535,6 +535,13 @@ 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