vtls: Fix a memory leak if an SSL session cannot be added to the cache

On connection shutdown, a new TLS session ticket may arrive after the
SSL session cache has already been destructed. In this case, the new
SSL session cannot be added to the SSL session cache.

The callers of Curl_ssl_addsessionid() need to know whether the SSL
session has been added to the cache. If it has not been added, the
reference counter of the SSL session must not be incremented, or memory
used by the SSL session must be freed. This is now possible with the new
output parameter "added" of Curl_ssl_addsessionid().

Fixes #7683
Closes #7752

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/vtls/mbedtls.c b/lib/vtls/mbedtls.c
index 780d13e18..08c79e162 100644
--- a/lib/vtls/mbedtls.c
+++ b/lib/vtls/mbedtls.c
@@ -784,6 +784,7 @@ mbed_connect_step3(struct Curl_easy *data, struct connectdata *conn,
     mbedtls_ssl_session *our_ssl_sessionid;
     void *old_ssl_sessionid = NULL;
     bool isproxy = SSL_IS_PROXY() ? TRUE : FALSE;
+    bool added = FALSE;
 
     our_ssl_sessionid = malloc(sizeof(mbedtls_ssl_session));
     if(!our_ssl_sessionid)
@@ -807,11 +808,13 @@ mbed_connect_step3(struct Curl_easy *data, struct connectdata *conn,
       Curl_ssl_delsessionid(data, old_ssl_sessionid);
 
     retcode = Curl_ssl_addsessionid(data, conn, isproxy, our_ssl_sessionid,
-                                    0, sockindex);
+                                    0, sockindex, &added);
     Curl_ssl_sessionid_unlock(data);
-    if(retcode) {
+    if(!added) {
       mbedtls_ssl_session_free(our_ssl_sessionid);
       free(our_ssl_sessionid);
+    }
+    if(retcode) {
       failf(data, "failed to store ssl session");
       return retcode;
     }