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Date: Tue, 3 Jun 2008 14:52:00 -0700
From: "Adam Langley" <agl@...erialviolet.org>
To: davem@...emloft.net
Cc: netdev@...r.kernel.org
Subject: [PATCH] Fix corrupt TCP packets when options space overflows with MD5SIG enabled (v2)
When MD5 signatures are turned on we can end up with syntactically invalid
packets with a header length < 20 bytes. This is because tcp_header_size
overflows with 12 bytes of timestamp, 20 bytes of signature and > 8 bytes of
SACK option.
Since we can't fit any SACK blocks in the final 8 bytes of options space, and
the MD5 signature is more important, we disable including SACK, or even
advertising it, when MD5 is enabled.
Signed-off-by: Adam Langley <agl@...erialviolet.org>
---
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index e399bde..ced7241 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -358,7 +358,7 @@ static void tcp_build_and_update_options(__be32 *ptr, struct tcp_sock *tp,
*ptr++ = htonl(tstamp);
*ptr++ = htonl(tp->rx_opt.ts_recent);
}
- if (tp->rx_opt.eff_sacks) {
+ if (!md5_hash && tp->rx_opt.eff_sacks) {
struct tcp_sack_block *sp = tp->rx_opt.dsack ? tp->duplicate_sack : tp->selective_acks;
int this_sack;
@@ -470,12 +470,12 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
gfp_t gfp_mask)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_md5sig_key *md5 = NULL;
struct inet_sock *inet;
struct tcp_sock *tp;
struct tcp_skb_cb *tcb;
int tcp_header_size;
#ifdef CONFIG_TCP_MD5SIG
- struct tcp_md5sig_key *md5;
__u8 *md5_hash_location;
#endif
struct tcphdr *th;
@@ -504,13 +504,25 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
tcb = TCP_SKB_CB(skb);
tcp_header_size = tp->tcp_header_len;
+ if (unlikely(tcb->flags & TCPCB_FLAG_SYN))
+ tcp_header_size = sizeof(struct tcphdr) + TCPOLEN_MSS;
+
+#ifdef CONFIG_TCP_MD5SIG
+ /*
+ * Are we doing MD5 on this segment? If so - make
+ * room for it.
+ */
+ md5 = tp->af_specific->md5_lookup(sk, sk);
+ if (md5)
+ tcp_header_size += TCPOLEN_MD5SIG_ALIGNED;
+#endif
+
#define SYSCTL_FLAG_TSTAMPS 0x1
#define SYSCTL_FLAG_WSCALE 0x2
#define SYSCTL_FLAG_SACK 0x4
sysctl_flags = 0;
if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
- tcp_header_size = sizeof(struct tcphdr) + TCPOLEN_MSS;
if (sysctl_tcp_timestamps) {
tcp_header_size += TCPOLEN_TSTAMP_ALIGNED;
sysctl_flags |= SYSCTL_FLAG_TSTAMPS;
@@ -519,12 +531,15 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
tcp_header_size += TCPOLEN_WSCALE_ALIGNED;
sysctl_flags |= SYSCTL_FLAG_WSCALE;
}
- if (sysctl_tcp_sack) {
+ /* We don't include SACK options if we are going to
+ * include an MD5 signature because they can't fit
+ * in the options space */
+ if (sysctl_tcp_sack && !md5) {
sysctl_flags |= SYSCTL_FLAG_SACK;
if (!(sysctl_flags & SYSCTL_FLAG_TSTAMPS))
tcp_header_size += TCPOLEN_SACKPERM_ALIGNED;
}
- } else if (unlikely(tp->rx_opt.eff_sacks)) {
+ } else if (unlikely(tp->rx_opt.eff_sacks && !md5)) {
/* A SACK is 2 pad bytes, a 2 byte header, plus
* 2 32-bit sequence numbers for each SACK block.
*/
@@ -536,16 +551,6 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
if (tcp_packets_in_flight(tp) == 0)
tcp_ca_event(sk, CA_EVENT_TX_START);
-#ifdef CONFIG_TCP_MD5SIG
- /*
- * Are we doing MD5 on this segment? If so - make
- * room for it.
- */
- md5 = tp->af_specific->md5_lookup(sk, sk);
- if (md5)
- tcp_header_size += TCPOLEN_MD5SIG_ALIGNED;
-#endif
-
skb_push(skb, tcp_header_size);
skb_reset_transport_header(skb);
skb_set_owner_w(skb, sk);
@@ -974,6 +979,7 @@ unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
u32 mss_now;
u16 xmit_size_goal;
int doing_tso = 0;
+ int md5_signing = 0;
mss_now = tp->mss_cache;
@@ -986,15 +992,17 @@ unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
mss_now = tcp_sync_mss(sk, mtu);
}
- if (tp->rx_opt.eff_sacks)
- mss_now -= (TCPOLEN_SACK_BASE_ALIGNED +
- (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK));
-
#ifdef CONFIG_TCP_MD5SIG
- if (tp->af_specific->md5_lookup(sk, sk))
+ if (tp->af_specific->md5_lookup(sk, sk)) {
+ md5_signing = 1;
mss_now -= TCPOLEN_MD5SIG_ALIGNED;
+ }
#endif
+ if (!md5_signing && tp->rx_opt.eff_sacks)
+ mss_now -= (TCPOLEN_SACK_BASE_ALIGNED +
+ (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK));
+
xmit_size_goal = mss_now;
if (doing_tso) {
@@ -2193,6 +2201,13 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
skb->dst = dst_clone(dst);
+#ifdef CONFIG_TCP_MD5SIG
+ md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
+ /* SACKs don't fit in the option space with MD5 sigs */
+ if (md5)
+ ireq->sack_ok = 0;
+#endif
+
tcp_header_size = (sizeof(struct tcphdr) + TCPOLEN_MSS +
(ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0) +
(ireq->wscale_ok ? TCPOLEN_WSCALE_ALIGNED : 0) +
@@ -2201,7 +2216,6 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
#ifdef CONFIG_TCP_MD5SIG
/* Are we doing MD5 on this segment? If so - make room for it */
- md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
if (md5)
tcp_header_size += TCPOLEN_MD5SIG_ALIGNED;
#endif
--
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