[PATCH 4.14 17/46] l2tp: remove l2specific_len dependency in l2tp_core

Greg Kroah-Hartman
2019-02-04T10:44:56Z

From: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>

commit 62e7b6a57c7b9bf3c6fd99418eeec05b08a85c38 upstream.

Remove l2specific_len dependency while building l2tpv3 header or
parsing the received frame since default L2-Specific Sublayer is
always four bytes long and we don't need to rely on a user supplied
value.
Moreover in l2tp netlink code there are no sanity checks to
enforce the relation between l2specific_len and l2specific_type,
so sending a malformed netlink message is possible to set
l2specific_type to L2TP_L2SPECTYPE_DEFAULT (or even
L2TP_L2SPECTYPE_NONE) and set l2specific_len to a value greater than
4 leaking memory on the wire and sending corrupted frames.

Reviewed-by: Guillaume Nault <g.nault@alphalink.fr>
Tested-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/l2tp/l2tp_core.c | 34 ++++++++++++++++------------------
net/l2tp/l2tp_core.h | 11 +++++++++++
2 files changed, 27 insertions(+), 18 deletions(-)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -758,11 +758,9 @@ void l2tp_recv_common(struct l2tp_sessio
"%s: recv data ns=%u, session nr=%u\n",
session->name, ns, session->nr);
}
+ ptr += 4;
}

- /* Advance past L2-specific header, if present */
- ptr += session->l2specific_len;
-
if (L2TP_SKB_CB(skb)->has_seq) {
/* Received a packet with sequence numbers. If we're the LNS,
* check if we sre sending sequence numbers and if not,
@@ -1084,21 +1082,20 @@ static int l2tp_build_l2tpv3_header(stru
memcpy(bufp, &session->cookie[0], session->cookie_len);
bufp += session->cookie_len;
}
- if (session->l2specific_len) {
- if (session->l2specific_type == L2TP_L2SPECTYPE_DEFAULT) {
- u32 l2h = 0;
- if (session->send_seq) {
- l2h = 0x40000000 | session->ns;
- session->ns++;
- session->ns &= 0xffffff;
- l2tp_dbg(session, L2TP_MSG_SEQ,
- "%s: updated ns to %u\n",
- session->name, session->ns);
- }
+ if (session->l2specific_type == L2TP_L2SPECTYPE_DEFAULT) {
+ u32 l2h = 0;

- *((__be32 *) bufp) = htonl(l2h);
+ if (session->send_seq) {
+ l2h = 0x40000000 | session->ns;
+ session->ns++;
+ session->ns &= 0xffffff;
+ l2tp_dbg(session, L2TP_MSG_SEQ,
+ "%s: updated ns to %u\n",
+ session->name, session->ns);
}
- bufp += session->l2specific_len;
+
+ *((__be32 *)bufp) = htonl(l2h);
+ bufp += 4;
}

return bufp - optr;
@@ -1764,7 +1761,7 @@ int l2tp_session_delete(struct l2tp_sess
EXPORT_SYMBOL_GPL(l2tp_session_delete);

/* We come here whenever a session's send_seq, cookie_len or
- * l2specific_len parameters are set.
+ * l2specific_type parameters are set.
*/
void l2tp_session_set_header_len(struct l2tp_session *session, int version)
{
@@ -1773,7 +1770,8 @@ void l2tp_session_set_header_len(struct
if (session->send_seq)
session->hdr_len += 4;
} else {
- session->hdr_len = 4 + session->cookie_len + session->l2specific_len;
+ session->hdr_len = 4 + session->cookie_len;
+ session->hdr_len += l2tp_get_l2specific_len(session);
if (session->tunnel->encap == L2TP_ENCAPTYPE_UDP)
session->hdr_len += 4;
}
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -320,6 +320,17 @@ do { \
#define l2tp_session_dec_refcount(s) l2tp_session_dec_refcount_1(s)
#endif

+static inline int l2tp_get_l2specific_len(struct l2tp_session *session)
+{
+ switch (session->l2specific_type) {
+ case L2TP_L2SPECTYPE_DEFAULT:
+ return 4;
+ case L2TP_L2SPECTYPE_NONE:
+ default:
+ return 0;
+ }
+}
+
#define l2tp_printk(ptr, type, func, fmt, ...) \
do { \
if (((ptr)->debug) & (type)) \