Phonet: fix flawed "SYN/ACK" logic

* Do not fail if the peer supports more or less than 3 algorithms.
 * Ignore unknown congestion control algorithms instead of failing.
 * Simplify congestion algorithm negotiation (largest is best).
 * Do not use a static buffer.
 * Fix off-by-two read overflow.
 * Avoid extra memory copy (in addition to skb_copy_bits()).

The previous code really made no sense.

Signed-off-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 47 insertions, 78 deletions

diff --git a/net/phonet/pep.c b/net/phonet/pep.c
index 0ecab59963e0..b8c31fc928e1 100644
--- a/net/phonet/pep.c
+++ b/net/phonet/pep.c
@@ -108,70 +108,6 @@ static int pep_reply(struct sock *sk, struct sk_buff *oskb,
 #define PAD 0x00
 
 #ifdef CONFIG_PHONET_PIPECTRLR
-static u8 pipe_negotiate_fc(u8 *host_fc, u8 *remote_fc, int len)
-{
-        int i, j;
-        u8 base_fc, final_fc;
-
-        for (i = 0; i < len; i++) {
-                base_fc = host_fc[i];
-                for (j = 0; j < len; j++) {
-                        if (remote_fc[j] == base_fc) {
-                                final_fc = base_fc;
-                                goto done;
-                        }
-                }
-        }
-        return -EINVAL;
-
-done:
-        return final_fc;
-
-}
-
-static int pipe_get_flow_info(struct sock *sk, struct sk_buff *skb,
-                u8 *pref_rx_fc, u8 *req_tx_fc)
-{
-        struct pnpipehdr *hdr;
-        u8 n_sb;
-
-        if (!pskb_may_pull(skb, sizeof(*hdr) + 4))
-                return -EINVAL;
-
-        hdr = pnp_hdr(skb);
-        n_sb = hdr->data[4];
-
-        __skb_pull(skb, sizeof(*hdr) + 4);
-        while (n_sb > 0) {
-                u8 type, buf[3], len = sizeof(buf);
-                u8 *data = pep_get_sb(skb, &type, &len, buf);
-
-                if (data == NULL)
-                        return -EINVAL;
-
-                switch (type) {
-                case PN_PIPE_SB_REQUIRED_FC_TX:
-                        if (len < 3 || (data[2] | data[3] | data[4]) > 3)
-                                break;
-                        req_tx_fc[0] = data[2];
-                        req_tx_fc[1] = data[3];
-                        req_tx_fc[2] = data[4];
-                        break;
-
-                case PN_PIPE_SB_PREFERRED_FC_RX:
-                        if (len < 3 || (data[2] | data[3] | data[4]) > 3)
-                                break;
-                        pref_rx_fc[0] = data[2];
-                        pref_rx_fc[1] = data[3];
-                        pref_rx_fc[2] = data[4];
-                        break;
-
-                }
-                n_sb--;
-        }
-        return 0;
-}
-
 static int pipe_handler_send_req(struct sock *sk, u8 msg_id, gfp_t priority)
 {
         int len;
@@ -661,28 +597,61 @@ static void pipe_destruct(struct sock *sk)
 }
 
 #ifdef CONFIG_PHONET_PIPECTRLR
+static u8 pipe_negotiate_fc(const u8 *fcs, unsigned n)
+{
+        unsigned i;
+        u8 final_fc = PN_NO_FLOW_CONTROL;
+
+        for (i = 0; i < n; i++) {
+                u8 fc = fcs[i];
+
+                if (fc > final_fc && fc < PN_MAX_FLOW_CONTROL)
+                        final_fc = fc;
+        }
+        return final_fc;
+}
+
 static int pep_connresp_rcv(struct sock *sk, struct sk_buff *skb)
 {
         struct pep_sock *pn = pep_sk(sk);
-        u8 host_pref_rx_fc[3] = {3, 2, 1}, host_req_tx_fc[3] = {3, 2, 1};
-        u8 remote_pref_rx_fc[3], remote_req_tx_fc[3];
-        u8 negotiated_rx_fc, negotiated_tx_fc;
-
-        pipe_get_flow_info(sk, skb, remote_pref_rx_fc,
-                        remote_req_tx_fc);
-        negotiated_tx_fc = pipe_negotiate_fc(remote_req_tx_fc,
-                        host_pref_rx_fc,
-                        sizeof(host_pref_rx_fc));
-        negotiated_rx_fc = pipe_negotiate_fc(host_req_tx_fc,
-                        remote_pref_rx_fc,
-                        sizeof(host_pref_rx_fc));
+        struct pnpipehdr *hdr;
+        u8 n_sb;
+
+        if (!pskb_pull(skb, sizeof(*hdr) + 4))
+                return -EINVAL;
+
+        hdr = pnp_hdr(skb);
+
+        /* Parse sub-blocks */
+        n_sb = hdr->data[4];
+        while (n_sb > 0) {
+                u8 type, buf[6], len = sizeof(buf);
+                const u8 *data = pep_get_sb(skb, &type, &len, buf);
+
+                if (data == NULL)
+                        return -EINVAL;
+
+                switch (type) {
+                case PN_PIPE_SB_REQUIRED_FC_TX:
+                        if (len < 2 || len < data[0])
+                                break;
+                        pn->tx_fc = pipe_negotiate_fc(data + 2, len - 2);
+                        break;
+
+                case PN_PIPE_SB_PREFERRED_FC_RX:
+                        if (len < 2 || len < data[0])
+                                break;
+                        pn->rx_fc = pipe_negotiate_fc(data + 2, len - 2);
+                        break;
+
+                }
+                n_sb--;
+        }
 
         sk->sk_state = TCP_SYN_RECV;
         sk->sk_backlog_rcv = pipe_do_rcv;
         sk->sk_destruct = pipe_destruct;
         pn->rx_credits = 0;
-        pn->rx_fc = negotiated_rx_fc;
-        pn->tx_fc = negotiated_tx_fc;
         sk->sk_state_change(sk);
 
         return pipe_handler_send_created_ind(sk, PNS_PIPE_CREATED_IND);