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l2tp: remove l2specific_len dependency in l2tp_core 

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>
This commit is contained in:
Lorenzo Bianconi 2018-01-16 23:01:55 +01:00 committed by syphyr
parent 3ed98e710a
commit f2110664d5
2 changed files with 27 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
net/l2tp/l2tp_core.c
View File

@ -730,11 +730,9 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
"%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,
@ -1083,21 +1081,20 @@ static int l2tp_build_l2tpv3_header(struct l2tp_session *session, void *buf)
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;
}
if (session->offset)
bufp += session->offset;
@ -1846,7 +1843,7 @@ int l2tp_session_delete(struct l2tp_session *session)
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.
*/
static void l2tp_session_set_header_len(struct l2tp_session *session, int version)
{
@ -1855,7 +1852,8 @@ static void l2tp_session_set_header_len(struct l2tp_session *session, int versio
if (session->send_seq)
session->hdr_len += 4;
} else {
session->hdr_len = 4 + session->cookie_len + session->l2specific_len + session->offset;
session->hdr_len = 4 + session->cookie_len + session->offset;
session->hdr_len += l2tp_get_l2specific_len(session);
if (session->tunnel->encap == L2TP_ENCAPTYPE_UDP)
session->hdr_len += 4;
}

11
net/l2tp/l2tp_core.h
View File

@ -301,6 +301,17 @@ 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)) \