[PATCH 12/19] tcp: ipv4: Add AO signing for skb-less replies

Leonard Crestez
2021-09-21T16:17:00Z

The code in tcp_v4_send_ack and tcp_v4_send_reset does not allocate a
full skb so special handling is required for tcp-authopt handling.

Signed-off-by: Leonard Crestez <cdleonard@gmail.com>
---
net/ipv4/tcp_ipv4.c | 79 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 76 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index e5c790795662..2d5fbe7690aa 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -641,10 +641,50 @@ void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb)

__tcp_v4_send_check(skb, inet->inet_saddr, inet->inet_daddr);
}
EXPORT_SYMBOL(tcp_v4_send_check);

+/** tcp_v4_authopt_handle_reply - Insert TCPOPT_AUTHOPT if required
+ *
+ * returns number of bytes (always aligned to 4) or zero
+ */
+static int tcp_v4_authopt_handle_reply(
+ const struct sock *sk,
+ struct sk_buff *skb,
+ __be32* optptr,
+ struct tcphdr *th)
+{
+ struct tcp_authopt_info *info;
+ struct tcp_authopt_key_info *key_info;
+ u8 rnextkeyid;
+
+ if (sk->sk_state == TCP_TIME_WAIT)
+ info = tcp_twsk(sk)->tw_authopt_info;
+ else
+ info = tcp_sk(sk)->authopt_info;
+ if (!info)
+ return 0;
+ key_info = __tcp_authopt_select_key(sk, info, sk, &rnextkeyid);
+ if (!key_info)
+ return 0;
+ *optptr = htonl((TCPOPT_AUTHOPT << 24) |
+ (TCPOLEN_AUTHOPT_OUTPUT << 16) |
+ (key_info->send_id << 8) |
+ (rnextkeyid));
+ /* must update doff before signature computation */
+ th->doff += TCPOLEN_AUTHOPT_OUTPUT / 4;
+ tcp_v4_authopt_hash_reply(
+ (char*)(optptr + 1),
+ info,
+ key_info,
+ ip_hdr(skb)->daddr,
+ ip_hdr(skb)->saddr,
+ th);
+
+ return TCPOLEN_AUTHOPT_OUTPUT;
+}
+
/*
* This routine will send an RST to the other tcp.
*
* Someone asks: why I NEVER use socket parameters (TOS, TTL etc.)
* for reset.
@@ -656,10 +696,12 @@ EXPORT_SYMBOL(tcp_v4_send_check);
* Exception: precedence violation. We do not implement it in any case.
*/

#ifdef CONFIG_TCP_MD5SIG
#define OPTION_BYTES TCPOLEN_MD5SIG_ALIGNED
+#elif defined(OPTION_BYTES_TCP_AUTHOPT)
+#define OPTION_BYTES TCPOLEN_AUTHOPT_OUTPUT
#else
#define OPTION_BYTES sizeof(__be32)
#endif

static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
@@ -709,12 +751,28 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
memset(&arg, 0, sizeof(arg));
arg.iov[0].iov_base = (unsigned char *)&rep;
arg.iov[0].iov_len = sizeof(rep.th);

net = sk ? sock_net(sk) : dev_net(skb_dst(skb)->dev);
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AUTHOPT)
rcu_read_lock();
+#endif
+#ifdef CONFIG_TCP_AUTHOPT
+ /* Unlike TCP-MD5 the signatures for TCP-AO depend on initial sequence
+ * numbers so we can only handle established and time-wait sockets.
+ *
+ * FIXME: What about RST in response to SYN?
+ */
+ if (static_branch_unlikely(&tcp_authopt_needed) && sk && sk->sk_state != TCP_NEW_SYN_RECV && sk->sk_state != TCP_LISTEN) {
+ int tcp_authopt_ret = tcp_v4_authopt_handle_reply(sk, skb, rep.opt, &rep.th);
+ if (tcp_authopt_ret) {
+ arg.iov[0].iov_len += tcp_authopt_ret;
+ goto skip_md5sig;
+ }
+ }
+#endif
+#ifdef CONFIG_TCP_MD5SIG
hash_location = tcp_parse_md5sig_option(th);
if (sk && sk_fullsock(sk)) {
const union tcp_md5_addr *addr;
int l3index;

@@ -752,11 +810,10 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
addr = (union tcp_md5_addr *)&ip_hdr(skb)->saddr;
key = tcp_md5_do_lookup(sk1, l3index, addr, AF_INET);
if (!key)
goto out;

-
genhash = tcp_v4_md5_hash_skb(newhash, key, NULL, skb);
if (genhash || memcmp(hash_location, newhash, 16) != 0)
goto out;

}
@@ -773,10 +830,11 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
tcp_v4_md5_hash_hdr((__u8 *) &rep.opt[1],
key, ip_hdr(skb)->saddr,
ip_hdr(skb)->daddr, &rep.th);
}
#endif
+skip_md5sig:
/* Can't co-exist with TCPMD5, hence check rep.opt[0] */
if (rep.opt[0] == 0) {
__be32 mrst = mptcp_reset_option(skb);

if (mrst) {
@@ -825,11 +883,11 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
ctl_sk->sk_mark = 0;
__TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
__TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
local_bh_enable();

-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AUTHOPT)
out:
rcu_read_unlock();
#endif
}

@@ -847,10 +905,12 @@ static void tcp_v4_send_ack(const struct sock *sk,
struct {
struct tcphdr th;
__be32 opt[(TCPOLEN_TSTAMP_ALIGNED >> 2)
#ifdef CONFIG_TCP_MD5SIG
+ (TCPOLEN_MD5SIG_ALIGNED >> 2)
+#elif defined (CONFIG_TCP_AUTHOPT)
+ + (TCPOLEN_AUTHOPT_OUTPUT >> 2)
#endif
];
} rep;
struct net *net = sock_net(sk);
struct ip_reply_arg arg;
@@ -878,10 +938,22 @@ static void tcp_v4_send_ack(const struct sock *sk,
rep.th.seq = htonl(seq);
rep.th.ack_seq = htonl(ack);
rep.th.ack = 1;
rep.th.window = htons(win);

+#ifdef CONFIG_TCP_AUTHOPT
+ if (static_branch_unlikely(&tcp_authopt_needed))
+ {
+ int offset = (tsecr) ? 3 : 0;
+
+ int tcp_authopt_ret = tcp_v4_authopt_handle_reply(sk, skb, &rep.opt[offset], &rep.th);
+ if (tcp_authopt_ret) {
+ arg.iov[0].iov_len += tcp_authopt_ret;
+ goto skip_md5sig;
+ }
+ }
+#endif
#ifdef CONFIG_TCP_MD5SIG
if (key) {
int offset = (tsecr) ? 3 : 0;

rep.opt[offset++] = htonl((TCPOPT_NOP << 24) |
@@ -894,10 +966,11 @@ static void tcp_v4_send_ack(const struct sock *sk,
tcp_v4_md5_hash_hdr((__u8 *) &rep.opt[offset],
key, ip_hdr(skb)->saddr,
ip_hdr(skb)->daddr, &rep.th);
}
#endif
+skip_md5sig:
arg.flags = reply_flags;
arg.csum = csum_tcpudp_nofold(ip_hdr(skb)->daddr,
ip_hdr(skb)->saddr, /* XXX */
arg.iov[0].iov_len, IPPROTO_TCP, 0);
arg.csumoffset = offsetof(struct tcphdr, check) / 2;
--
2.25.1