l2tp: check sockaddr length in pppol2tp_connect()

Check sockaddr_len before dereferencing sp->sa_protocol, to ensure that
it actually points to valid data.

Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Reported-by: syzbot+a70ac890b23b1bf29f5c@syzkaller.appspotmail.com
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 1404bc1c1bb7..1fd9e145076a 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -619,6 +619,13 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
         lock_sock(sk);
 
         error = -EINVAL;
+
+        if (sockaddr_len != sizeof(struct sockaddr_pppol2tp) &&
+            sockaddr_len != sizeof(struct sockaddr_pppol2tpv3) &&
+            sockaddr_len != sizeof(struct sockaddr_pppol2tpin6) &&
+            sockaddr_len != sizeof(struct sockaddr_pppol2tpv3in6))
+                goto end;
+
         if (sp->sa_protocol != PX_PROTO_OL2TP)
                 goto end;