[PATCH 4.4 41/65] l2tp: fix reading optional fields of L2TPv3

Greg Kroah-Hartman
2019-02-04T11:08:43Z

From: Jacob Wen <jian.w.wen@oracle.com>

[ Upstream commit 4522a70db7aa5e77526a4079628578599821b193 ]

Use pskb_may_pull() to make sure the optional fields are in skb linear
parts, so we can safely read them later.

It's easy to reproduce the issue with a net driver that supports paged
skb data. Just create a L2TPv3 over IP tunnel and then generates some
network traffic.
Once reproduced, rx err in /sys/kernel/debug/l2tp/tunnels will increase.

Changes in v4:
1. s/l2tp_v3_pull_opt/l2tp_v3_ensure_opt_in_linear/
2. s/tunnel->version != L2TP_HDR_VER_2/tunnel->version == L2TP_HDR_VER_3/
3. Add 'Fixes' in commit messages.

Changes in v3:
1. To keep consistency, move the code out of l2tp_recv_common.
2. Use "net" instead of "net-next", since this is a bug fix.

Changes in v2:
1. Only fix L2TPv3 to make code simple.
To fix both L2TPv3 and L2TPv2, we'd better refactor l2tp_recv_common.
It's complicated to do so.
2. Reloading pointers after pskb_may_pull

Fixes: f7faffa3ff8e ("l2tp: Add L2TPv3 protocol support")
Fixes: 0d76751fad77 ("l2tp: Add L2TPv3 IP encapsulation (no UDP) support")
Fixes: a32e0eec7042 ("l2tp: introduce L2TPv3 IP encapsulation support for IPv6")
Signed-off-by: Jacob Wen <jian.w.wen@oracle.com>
Acked-by: Guillaume Nault <gnault@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 | 4 ++++
net/l2tp/l2tp_core.h | 20 ++++++++++++++++++++
net/l2tp/l2tp_ip.c | 3 +++
net/l2tp/l2tp_ip6.c | 3 +++
4 files changed, 30 insertions(+)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -930,6 +930,10 @@ static int l2tp_udp_recv_core(struct l2t
goto error;
}

+ if (tunnel->version == L2TP_HDR_VER_3 &&
+ l2tp_v3_ensure_opt_in_linear(session, skb, &ptr, &optr))
+ goto error;
+
l2tp_recv_common(session, skb, ptr, optr, hdrflags, length, payload_hook);

return 0;
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -324,6 +324,26 @@ static inline int l2tp_get_l2specific_le
}
}

+static inline int l2tp_v3_ensure_opt_in_linear(struct l2tp_session *session, struct sk_buff *skb,
+ unsigned char **ptr, unsigned char **optr)
+{
+ int opt_len = session->peer_cookie_len + l2tp_get_l2specific_len(session);
+
+ if (opt_len > 0) {
+ int off = *ptr - *optr;
+
+ if (!pskb_may_pull(skb, off + opt_len))
+ return -1;
+
+ if (skb->data != *optr) {
+ *optr = skb->data;
+ *ptr = skb->data + off;
+ }
+ }
+
+ return 0;
+}
+
#define l2tp_printk(ptr, type, func, fmt, ...) \
do { \
if (((ptr)->debug) & (type)) \
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -163,6 +163,9 @@ static int l2tp_ip_recv(struct sk_buff *
print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, ptr, length);
}

+ if (l2tp_v3_ensure_opt_in_linear(session, skb, &ptr, &optr))
+ goto discard;
+
l2tp_recv_common(session, skb, ptr, optr, 0, skb->len, tunnel->recv_payload_hook);

return 0;
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -174,6 +174,9 @@ static int l2tp_ip6_recv(struct sk_buff
print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, ptr, length);
}

+ if (l2tp_v3_ensure_opt_in_linear(session, skb, &ptr, &optr))
+ goto discard;
+
l2tp_recv_common(session, skb, ptr, optr, 0, skb->len,
tunnel->recv_payload_hook);
return 0;