Fix SSL_CTX_add_session: When two SSL_SESSIONs have the same ID,

they can sometimes be different memory structures.

diff --git a/CHANGES b/CHANGES
index 225e4cfa1139e46d784f4b063eee2c3ad0b072b0..acf8bcd7ecda8013c91634362e5e69472c193bc8 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,14 @@
 
  Changes between 0.9.4 and 0.9.5  [xx XXX 1999]
 
+  *) In SSL_CTX_add_session, take into account that there might be multiple
+     SSL_SESSION structures with the same session ID (e.g. when two threads
+     concurrently obtain them from an external cache).
+     The internal cache can handle only one SSL_SESSION with a given ID,
+     so if there's a conflict, we now throw out the old one to achieve
+     consistency.
+     [Bodo Moeller]
+
   *) Add OIDs for idea and blowfish in CBC mode. This will allow both
      to be used in PKCS#5 v2.0 and S/MIME.  Also add checking to
      some routines that use cipher OIDs: some ciphers do not have OIDs

diff --git a/ssl/ssl_sess.c b/ssl/ssl_sess.c
index 74ec2178a936a0cadcf62cb6e7ddbc6aababd022..d6755801cc6540443fecd25eac4c0bd8f20bb2bd 100644 (file)
--- a/ssl/ssl_sess.c
+++ b/ssl/ssl_sess.c
@@ -191,8 +191,14 @@ int ssl_get_new_session(SSL *s, int session)
                        CRYPTO_r_unlock(CRYPTO_LOCK_SSL_CTX);
                        if (r == NULL) break;
                        /* else - woops a session_id match */
-                       /* XXX should also check external cache!
-                        * (But the probability of a collision is negligible, anyway...) */
+                       /* XXX We should also check the external cache --
+                        * but the probability of a collision is negligible, and
+                        * we could not prevent the concurrent creation of sessions
+                        * with identical IDs since we currently don't have means
+                        * to atomically check whether a session ID already exists
+                        * and make a reservation for it if it does not
+                        * (this problem applies to the internal cache as well).
+                        */
                        }
                }
        else
@@ -216,7 +222,6 @@ int ssl_get_prev_session(SSL *s, unsigned char *session_id, int len)
        SSL_SESSION *ret=NULL,data;
        int fatal = 0;
 
-       /* conn_init();*/
        data.ssl_version=s->version;
        data.session_id_length=len;
        if (len > SSL_MAX_SSL_SESSION_ID_LENGTH)
@@ -352,27 +357,47 @@ int SSL_CTX_add_session(SSL_CTX *ctx, SSL_SESSION *c)
        int ret=0;
        SSL_SESSION *s;
 
-       /* conn_init(); */
+       /* add just 1 reference count for the SSL_CTX's session cache
+        * even though it has two ways of access: each session is in a
+        * doubly linked list and an lhash */
        CRYPTO_add(&c->references,1,CRYPTO_LOCK_SSL_SESSION);
+       /* if session c is in already in cache, we take back the increment later */
 
        CRYPTO_w_lock(CRYPTO_LOCK_SSL_CTX);
        s=(SSL_SESSION *)lh_insert(ctx->sessions,(char *)c);
        
-       /* Put on the end of the queue unless it is already in the cache */
+       /* s != NULL iff we already had a session with the given PID.
+        * In this case, s == c should hold (then we did not really modify
+        * ctx->sessions), or we're in trouble. */
+       if (s != NULL && s != c)
+               {
+               /* We *are* in trouble ... */
+               SSL_SESSION_list_remove(ctx,s);
+               SSL_SESSION_free(s);
+               /* ... so pretend the other session did not exist in cache
+                * (we cannot handle two SSL_SESSION structures with identical
+                * session ID in the same cache, which could happen e.g. when
+                * two threads concurrently obtain the same session from an external
+                * cache) */
+               s = NULL;
+               }
+
+       /* Put at the head of the queue unless it is already in the cache */
        if (s == NULL)
                SSL_SESSION_list_add(ctx,c);
 
-       /* If the same session if is being 're-added', Free the old
-        * one when the last person stops using it.
-        * This will also work if it is alread in the cache.
-        * The references will go up and then down :-) */
        if (s != NULL)
                {
-               SSL_SESSION_free(s);
+               /* existing cache entry -- decrement previously incremented reference
+                * count because it already takes into account the cache */
+
+               SSL_SESSION_free(s); /* s == c */
                ret=0;
                }
        else
                {
+               /* new cache entry -- remove old ones if cache has become too large */
+               
                ret=1;
 
                if (SSL_CTX_sess_get_cache_size(ctx) > 0)