From 4ea2739ea89883ddf79980a8aa27d5e57093e464 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 17 Oct 2011 17:59:53 +0000
Subject: [PATCH] pptp: pptp_rcv_core() misses pskb_may_pull() call
e1000e uses paged frags, so any layer incorrectly pulling bytes from skb
can trigger a BUG in skb_pull()
[951.142737] [<ffffffff813d2f36>] skb_pull+0x15/0x17
[951.142737] [<ffffffffa0286824>] pptp_rcv_core+0x126/0x19a [pptp]
[951.152725] [<ffffffff813d17c4>] sk_receive_skb+0x69/0x105
[951.163558] [<ffffffffa0286993>] pptp_rcv+0xc8/0xdc [pptp]
[951.165092] [<ffffffffa02800a3>] gre_rcv+0x62/0x75 [gre]
[951.165092] [<ffffffff81410784>] ip_local_deliver_finish+0x150/0x1c1
[951.177599] [<ffffffff81410634>] ? ip_local_deliver_finish+0x0/0x1c1
[951.177599] [<ffffffff81410846>] NF_HOOK.clone.7+0x51/0x58
[951.177599] [<ffffffff81410996>] ip_local_deliver+0x51/0x55
[951.177599] [<ffffffff814105b9>] ip_rcv_finish+0x31a/0x33e
[951.177599] [<ffffffff8141029f>] ? ip_rcv_finish+0x0/0x33e
[951.204898] [<ffffffff81410846>] NF_HOOK.clone.7+0x51/0x58
[951.214651] [<ffffffff81410bb5>] ip_rcv+0x21b/0x246
pptp_rcv_core() is a nice example of a function assuming everything it
needs is available in skb head.
Reported-by: Bradley Peterson <despite@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
drivers/net/pptp.c | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/drivers/net/pptp.c b/drivers/net/pptp.c
index 9c0403d0107c..89f829f5f725 100644
--- a/drivers/net/pptp.c
+++ b/drivers/net/pptp.c
@@ -307,11 +307,18 @@ static int pptp_rcv_core(struct sock *sk, struct sk_buff *skb)
}
header = (struct pptp_gre_header *)(skb->data);
+ headersize = sizeof(*header);
/* test if acknowledgement present */
if (PPTP_GRE_IS_A(header->ver)) {
- __u32 ack = (PPTP_GRE_IS_S(header->flags)) ?
- header->ack : header->seq; /* ack in different place if S = 0 */
+ __u32 ack;
+
+ if (!pskb_may_pull(skb, headersize))
+ goto drop;
+ header = (struct pptp_gre_header *)(skb->data);
+
+ /* ack in different place if S = 0 */
+ ack = PPTP_GRE_IS_S(header->flags) ? header->ack : header->seq;
ack = ntohl(ack);
@@ -320,21 +327,18 @@ static int pptp_rcv_core(struct sock *sk, struct sk_buff *skb)
/* also handle sequence number wrap-around */
if (WRAPPED(ack, opt->ack_recv))
opt->ack_recv = ack;
+ } else {
+ headersize -= sizeof(header->ack);
}
-
/* test if payload present */
if (!PPTP_GRE_IS_S(header->flags))
goto drop;
- headersize = sizeof(*header);
payload_len = ntohs(header->payload_len);
seq = ntohl(header->seq);
- /* no ack present? */
- if (!PPTP_GRE_IS_A(header->ver))
- headersize -= sizeof(header->ack);
/* check for incomplete packet (length smaller than expected) */
- if (skb->len - headersize < payload_len)
+ if (!pskb_may_pull(skb, headersize + payload_len))
goto drop;
payload = skb->data + headersize;
--
2.20.1