pppd: Make MSCHAP-v2 cope better with packet loss

[ppp.git] / pppd / chap_ms.c

diff --git a/pppd/chap_ms.c b/pppd/chap_ms.c
index aec12262ed46375d304b12f9b397acb88be21ba4..016b42e0c10ee9a845a3e96ad8aa55dcb2b0464c 100644 (file)
--- a/pppd/chap_ms.c
+++ b/pppd/chap_ms.c
@@ -320,25 +320,90 @@ chapms_make_response(unsigned char *response, int id, char *our_name,
        ChapMS(challenge, secret, secret_len, response);
 }
 
+struct chapms2_response_cache_entry {
+       int id;
+       unsigned char challenge[16];
+       unsigned char response[MS_CHAP2_RESPONSE_LEN];
+       unsigned char auth_response[MS_AUTH_RESPONSE_LENGTH];
+};
+
+#define CHAPMS2_MAX_RESPONSE_CACHE_SIZE 10
+static struct chapms2_response_cache_entry
+    chapms2_response_cache[CHAPMS2_MAX_RESPONSE_CACHE_SIZE];
+static int chapms2_response_cache_next_index = 0;
+static int chapms2_response_cache_size = 0;
+
+static void
+chapms2_add_to_response_cache(int id, unsigned char *challenge,
+                             unsigned char *response,
+                             unsigned char *auth_response)
+{
+       int i = chapms2_response_cache_next_index;
+
+       chapms2_response_cache[i].id = id;
+       memcpy(chapms2_response_cache[i].challenge, challenge, 16);
+       memcpy(chapms2_response_cache[i].response, response,
+              MS_CHAP2_RESPONSE_LEN);
+       memcpy(chapms2_response_cache[i].auth_response,
+              auth_response, MS_AUTH_RESPONSE_LENGTH);
+       chapms2_response_cache_next_index =
+               (i + 1) % CHAPMS2_MAX_RESPONSE_CACHE_SIZE;
+       if (chapms2_response_cache_next_index > chapms2_response_cache_size)
+               chapms2_response_cache_size = chapms2_response_cache_next_index;
+       dbglog("added response cache entry %d", i);
+}
+
+static struct chapms2_response_cache_entry*
+chapms2_find_in_response_cache(int id, unsigned char *challenge,
+                     unsigned char *auth_response)
+{
+       int i;
+
+       for (i = 0; i < chapms2_response_cache_size; i++) {
+               if (id == chapms2_response_cache[i].id
+                   && (!challenge
+                       || memcmp(challenge,
+                                 chapms2_response_cache[i].challenge,
+                                 16) == 0)
+                   && (!auth_response
+                       || memcmp(auth_response,
+                                 chapms2_response_cache[i].auth_response,
+                                 MS_AUTH_RESPONSE_LENGTH) == 0)) {
+                       dbglog("response found in cache (entry %d)", i);
+                       return &chapms2_response_cache[i];
+               }
+       }
+       return NULL;  /* not found */
+}
+
 static void
 chapms2_make_response(unsigned char *response, int id, char *our_name,
                      unsigned char *challenge, char *secret, int secret_len,
                      unsigned char *private)
 {
+       const struct chapms2_response_cache_entry *cache_entry;
+       unsigned char auth_response[MS_AUTH_RESPONSE_LENGTH];
+
        challenge++;    /* skip length, should be 16 */
        *response++ = MS_CHAP2_RESPONSE_LEN;
+       cache_entry = chapms2_find_in_response_cache(id, challenge, NULL);
+       if (cache_entry) {
+               memcpy(response, cache_entry->response, MS_CHAP2_RESPONSE_LEN);
+               return;
+       }
        ChapMS2(challenge,
 #ifdef DEBUGMPPEKEY
                mschap2_peer_challenge,
 #else
                NULL,
 #endif
-               our_name, secret, secret_len, response, private,
+               our_name, secret, secret_len, response, auth_response,
                MS_CHAP2_AUTHENTICATEE);
+       chapms2_add_to_response_cache(id, challenge, response, auth_response);
 }
 
 static int
-chapms2_check_success(unsigned char *msg, int len, unsigned char *private)
+chapms2_check_success(int id, unsigned char *msg, int len)
 {
        if ((len < MS_AUTH_RESPONSE_LENGTH + 2) ||
            strncmp((char *)msg, "S=", 2) != 0) {
@@ -349,7 +414,7 @@ chapms2_check_success(unsigned char *msg, int len, unsigned char *private)
        msg += 2;
        len -= 2;
        if (len < MS_AUTH_RESPONSE_LENGTH
-           || memcmp(msg, private, MS_AUTH_RESPONSE_LENGTH)) {
+           || !chapms2_find_in_response_cache(id, NULL /* challenge */, msg)) {
                /* Authenticator Response did not match expected. */
                error("MS-CHAPv2 mutual authentication failed.");
                return 0;