[PATCH 11/19] tcp: authopt: Add support for signing skb-less replies

Leonard Crestez
2021-09-21T16:17:50Z

This is required because tcp ipv4 sometimes sends replies without
allocating a full skb that can be signed by tcp authopt.

Handle this with additional code in tcp authopt.

Signed-off-by: Leonard Crestez <cdleonard@gmail.com>
---
include/net/tcp_authopt.h | 7 ++
net/ipv4/tcp_authopt.c | 147 ++++++++++++++++++++++++++++++++++++++
2 files changed, 154 insertions(+)

diff --git a/include/net/tcp_authopt.h b/include/net/tcp_authopt.h
index 422f0034d32b..b012eaaf416f 100644
--- a/include/net/tcp_authopt.h
+++ b/include/net/tcp_authopt.h
@@ -81,10 +81,17 @@ static inline struct tcp_authopt_key_info *tcp_authopt_select_key(
}
int tcp_authopt_hash(
char *hash_location,
struct tcp_authopt_key_info *key,
struct sock *sk, struct sk_buff *skb);
+int tcp_v4_authopt_hash_reply(
+ char *hash_location,
+ struct tcp_authopt_info *info,
+ struct tcp_authopt_key_info *key,
+ __be32 saddr,
+ __be32 daddr,
+ struct tcphdr *th);
int __tcp_authopt_openreq(struct sock *newsk, const struct sock *oldsk, struct request_sock *req);
static inline int tcp_authopt_openreq(
struct sock *newsk,
const struct sock *oldsk,
struct request_sock *req)
diff --git a/net/ipv4/tcp_authopt.c b/net/ipv4/tcp_authopt.c
index 41f844d5d49a..756182401a3b 100644
--- a/net/ipv4/tcp_authopt.c
+++ b/net/ipv4/tcp_authopt.c
@@ -798,10 +798,74 @@ static int tcp_authopt_get_traffic_key(struct sock *sk,
out:
tcp_authopt_put_kdf_shash(key, kdf_tfm);
return err;
}

+struct tcp_v4_authopt_context_data {
+ __be32 saddr;
+ __be32 daddr;
+ __be16 sport;
+ __be16 dport;
+ __be32 sisn;
+ __be32 disn;
+ __be16 digestbits;
+} __packed;
+
+static int tcp_v4_authopt_get_traffic_key_noskb(
+ struct tcp_authopt_key_info *key,
+ __be32 saddr,
+ __be32 daddr,
+ __be16 sport,
+ __be16 dport,
+ __be32 sisn,
+ __be32 disn,
+ u8 *traffic_key)
+{
+ int err;
+ struct crypto_shash *kdf_tfm;
+ SHASH_DESC_ON_STACK(desc, kdf_tfm);
+ struct tcp_v4_authopt_context_data data;
+ BUILD_BUG_ON(sizeof(data) != 22);
+
+ kdf_tfm = tcp_authopt_get_kdf_shash(key);
+ if (IS_ERR(kdf_tfm))
+ return PTR_ERR(kdf_tfm);
+
+ err = tcp_authopt_setkey(kdf_tfm, key);
+ if (err)
+ goto out;
+
+ desc->tfm = kdf_tfm;
+ err = crypto_shash_init(desc);
+ if (err)
+ goto out;
+
+ // RFC5926 section 3.1.1.1
+ // Separate to keep alignment semi-sane
+ err = crypto_shash_update(desc, "\x01TCP-AO", 7);
+ if (err)
+ return err;
+ data.saddr = saddr;
+ data.daddr = daddr;
+ data.sport = sport;
+ data.dport = dport;
+ data.sisn = sisn;
+ data.disn = disn;
+ data.digestbits = htons(crypto_shash_digestsize(desc->tfm) * 8);
+
+ err = crypto_shash_update(desc, (u8*)&data, sizeof(data));
+ if (err)
+ goto out;
+ err = crypto_shash_final(desc, traffic_key);
+ if (err)
+ goto out;
+
+out:
+ tcp_authopt_put_kdf_shash(key, kdf_tfm);
+ return err;
+}
+
static int crypto_shash_update_zero(struct shash_desc *desc, int len)
{
u8 zero = 0;
int i, err;

@@ -1122,10 +1186,93 @@ int tcp_authopt_hash(char *hash_location,
memcpy(hash_location, macbuf, TCP_AUTHOPT_MACLEN);

return 0;
}

+/**
+ * tcp_v4_authopt_hash_hdr - Hash tcp+ipv4 header without SKB
+ *
+ * The key must come from tcp_authopt_select_key.
+ */
+int tcp_v4_authopt_hash_reply(char *hash_location,
+ struct tcp_authopt_info *info,
+ struct tcp_authopt_key_info *key,
+ __be32 saddr,
+ __be32 daddr,
+ struct tcphdr *th)
+{
+ struct crypto_shash *mac_tfm;
+ u8 macbuf[TCP_AUTHOPT_MAXMACBUF];
+ u8 traffic_key[TCP_AUTHOPT_MAX_TRAFFIC_KEY_LEN];
+ SHASH_DESC_ON_STACK(desc, tfm);
+ __be32 sne = 0;
+ int err;
+
+ /* Call special code path for computing traffic key without skb
+ * This can be called from tcp_v4_reqsk_send_ack so caching would be
+ * difficult here.
+ */
+ err = tcp_v4_authopt_get_traffic_key_noskb(
+ key,
+ saddr,
+ daddr,
+ th->source,
+ th->dest,
+ htonl(info->src_isn),
+ htonl(info->dst_isn),
+ traffic_key);
+ if (err)
+ goto out_err_traffic_key;
+
+ /* Init mac shash */
+ mac_tfm = tcp_authopt_get_mac_shash(key);
+ if (IS_ERR(mac_tfm))
+ return PTR_ERR(mac_tfm);
+ err = crypto_shash_setkey(mac_tfm, traffic_key, key->alg->traffic_key_len);
+ if (err)
+ goto out_err;
+
+ desc->tfm = mac_tfm;
+ err = crypto_shash_init(desc);
+ if (err)
+ return err;
+
+ err = crypto_shash_update(desc, (u8 *)&sne, 4);
+ if (err)
+ return err;
+
+ err = tcp_authopt_hash_tcp4_pseudoheader(desc, saddr, daddr, th->doff * 4);
+ if (err)
+ return err;
+
+ // TCP header with checksum set to zero. Caller ensures this.
+ if (WARN_ON_ONCE(th->check != 0))
+ goto out_err;
+ err = crypto_shash_update(desc, (u8 *)th, sizeof(*th));
+ if (err)
+ goto out_err;
+
+ // TCP options
+ err = tcp_authopt_hash_opts(desc, th, !(key->flags & TCP_AUTHOPT_KEY_EXCLUDE_OPTS));
+ if (err)
+ goto out_err;
+
+ err = crypto_shash_final(desc, macbuf);
+ if (err)
+ goto out_err;
+ memcpy(hash_location, macbuf, TCP_AUTHOPT_MACLEN);
+
+ tcp_authopt_put_mac_shash(key, mac_tfm);
+ return 0;
+
+out_err:
+ tcp_authopt_put_mac_shash(key, mac_tfm);
+out_err_traffic_key:
+ memset(hash_location, 0, TCP_AUTHOPT_MACLEN);
+ return err;
+}
+
static struct tcp_authopt_key_info *tcp_authopt_lookup_recv(struct sock *sk,
struct sk_buff *skb,
struct tcp_authopt_info *info,
int recv_id)
{
--
2.25.1