Remove arbitrary limitation on length of common name in SSL certificates.

Both libpq and the backend would truncate a common name extracted from a
certificate at 32 bytes.  Replace that fixed-size buffer with dynamically
allocated string so that there is no hard limit.  While at it, remove the
code for extracting peer_dn, which we weren't using for anything; and
don't bother to store peer_cn longer than we need it in libpq.

This limit was not so terribly unreasonable when the code was written,
because we weren't using the result for anything critical, just logging it.
But now that there are options for checking the common name against the
server host name (in libpq) or using it as the user's name (in the server),
this could result in undesirable failures.  In the worst case it even seems
possible to spoof a server name or user name, if the correct name is
exactly 32 bytes and the attacker can persuade a trusted CA to issue a
certificate in which that string is a prefix of the certificate's common
name.  (To exploit this for a server name, he'd also have to send the
connection astray via phony DNS data or some such.)  The case that this is
a realistic security threat is a bit thin, but nonetheless we'll treat it
as one.

Back-patch to 8.4.  Older releases contain the faulty code, but it's not
a security problem because the common name wasn't used for anything
interesting.

Reported and patched by Heikki Linnakangas

Security: CVE-2012-0867

diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index 8e8d745a00f03a5cd6660d806048d676f8631316..8964870e08a8cd065f000f505db9a6b1837fdfdb 100644 (file)
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -73,6 +73,7 @@
 
 #include "libpq/libpq.h"
 #include "tcop/tcopprot.h"
+#include "utils/memutils.h"
 
 
 #ifdef USE_SSL
@@ -964,44 +965,54 @@ aloop:
 
        port->count = 0;
 
-       /* get client certificate, if available. */
+       /* Get client certificate, if available. */
        port->peer = SSL_get_peer_certificate(port->ssl);
-       if (port->peer == NULL)
-       {
-               strlcpy(port->peer_dn, "(anonymous)", sizeof(port->peer_dn));
-               strlcpy(port->peer_cn, "(anonymous)", sizeof(port->peer_cn));
-       }
-       else
+
+       /* and extract the Common Name from it. */
+       port->peer_cn = NULL;
+       if (port->peer != NULL)
        {
-               X509_NAME_oneline(X509_get_subject_name(port->peer),
-                                                 port->peer_dn, sizeof(port->peer_dn));
-               port->peer_dn[sizeof(port->peer_dn) - 1] = '\0';
-               r = X509_NAME_get_text_by_NID(X509_get_subject_name(port->peer),
-                                          NID_commonName, port->peer_cn, sizeof(port->peer_cn));
-               port->peer_cn[sizeof(port->peer_cn) - 1] = '\0';
-               if (r == -1)
-               {
-                       /* Unable to get the CN, set it to blank so it can't be used */
-                       port->peer_cn[0] = '\0';
-               }
-               else
+               int             len;
+
+               len = X509_NAME_get_text_by_NID(X509_get_subject_name(port->peer),
+                                                                               NID_commonName, NULL, 0);
+               if (len != -1)
                {
+                       char       *peer_cn;
+
+                       peer_cn = MemoryContextAlloc(TopMemoryContext, len + 1);
+                       r = X509_NAME_get_text_by_NID(X509_get_subject_name(port->peer),
+                                                                                 NID_commonName, peer_cn, len + 1);
+                       peer_cn[len] = '\0';
+                       if (r != len)
+                       {
+                               /* shouldn't happen */
+                               pfree(peer_cn);
+                               close_SSL(port);
+                               return -1;
+                       }
+
                        /*
                         * Reject embedded NULLs in certificate common name to prevent
                         * attacks like CVE-2009-4034.
                         */
-                       if (r != strlen(port->peer_cn))
+                       if (len != strlen(peer_cn))
                        {
                                ereport(COMMERROR,
                                                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                                                 errmsg("SSL certificate's common name contains embedded null")));
+                               pfree(peer_cn);
                                close_SSL(port);
                                return -1;
                        }
+
+                       port->peer_cn = peer_cn;
                }
        }
+
        ereport(DEBUG2,
-                       (errmsg("SSL connection from \"%s\"", port->peer_cn)));
+                       (errmsg("SSL connection from \"%s\"",
+                                       port->peer_cn ? port->peer_cn : "(anonymous)")));
 
        /* set up debugging/info callback */
        SSL_CTX_set_info_callback(SSL_context, info_cb);
@@ -1027,6 +1038,12 @@ close_SSL(Port *port)
                X509_free(port->peer);
                port->peer = NULL;
        }
+
+       if (port->peer_cn)
+       {
+               pfree(port->peer_cn);
+               port->peer_cn = NULL;
+       }
 }
 
 /*

diff --git a/src/include/libpq/libpq-be.h b/src/include/libpq/libpq-be.h
index 6ee4714489bd1a3da7b16a68a9c8e2eeaab824a2..bf579c6cc79e0a4c7df91d9f2122e0e91e3dac38 100644 (file)
--- a/src/include/libpq/libpq-be.h
+++ b/src/include/libpq/libpq-be.h
@@ -167,8 +167,7 @@ typedef struct Port
 #ifdef USE_SSL
        SSL                *ssl;
        X509       *peer;
-       char            peer_dn[128 + 1];
-       char            peer_cn[SM_USER + 1];
+       char       *peer_cn;
        unsigned long count;
 #endif
 } Port;

diff --git a/src/interfaces/libpq/fe-secure.c b/src/interfaces/libpq/fe-secure.c
index 9833385c41ed914e4827fd7290d9407d7d6b87fc..29936deb9d1a7a2bd04457a03a73042690ec6b03 100644 (file)
--- a/src/interfaces/libpq/fe-secure.c
+++ b/src/interfaces/libpq/fe-secure.c
@@ -733,6 +733,11 @@ wildcard_certificate_match(const char *pattern, const char *string)
 static bool
 verify_peer_name_matches_certificate(PGconn *conn)
 {
+       char       *peer_cn;
+       int                     r;
+       int                     len;
+       bool            result;
+
        /*
         * If told not to verify the peer name, don't do it. Return true indicating
         * that the verification was successful.
@@ -740,33 +745,81 @@ verify_peer_name_matches_certificate(PGconn *conn)
        if (strcmp(conn->sslmode, "verify-full") != 0)
                return true;
 
+       /*
+        * Extract the common name from the certificate.
+        *
+        * XXX: Should support alternate names here
+        */
+       /* First find out the name's length and allocate a buffer for it. */
+       len = X509_NAME_get_text_by_NID(X509_get_subject_name(conn->peer),
+                                                                       NID_commonName, NULL, 0);
+       if (len == -1)
+       {
+               printfPQExpBuffer(&conn->errorMessage,
+                                                 libpq_gettext("could not get server common name from server certificate\n"));
+               return false;
+       }
+       peer_cn = malloc(len + 1);
+       if (peer_cn == NULL)
+       {
+               printfPQExpBuffer(&conn->errorMessage,
+                                                 libpq_gettext("out of memory\n"));
+               return false;
+       }
+
+       r = X509_NAME_get_text_by_NID(X509_get_subject_name(conn->peer),
+                                                                 NID_commonName, peer_cn, len + 1);
+       if (r != len)
+       {
+               /* Got different length than on the first call. Shouldn't happen. */
+               printfPQExpBuffer(&conn->errorMessage,
+                                                 libpq_gettext("could not get server common name from server certificate\n"));
+               free(peer_cn);
+               return false;
+       }
+       peer_cn[len] = '\0';
+
+       /*
+        * Reject embedded NULLs in certificate common name to prevent attacks
+        * like CVE-2009-4034.
+        */
+       if (len != strlen(peer_cn))
+       {
+               printfPQExpBuffer(&conn->errorMessage,
+                                                 libpq_gettext("SSL certificate's common name contains embedded null\n"));
+               free(peer_cn);
+               return false;
+       }
+
+       /*
+        * We got the peer's common name. Now compare it against the originally
+        * given hostname.
+        */
        if (!(conn->pghost && conn->pghost[0] != '\0'))
        {
                printfPQExpBuffer(&conn->errorMessage,
                                                  libpq_gettext("host name must be specified for a verified SSL connection\n"));
-               return false;
+               result = false;
        }
        else
        {
-               /*
-                * Compare CN to originally given hostname.
-                *
-                * XXX: Should support alternate names here
-                */
-               if (pg_strcasecmp(conn->peer_cn, conn->pghost) == 0)
+               if (pg_strcasecmp(peer_cn, conn->pghost) == 0)
                        /* Exact name match */
-                       return true;
-               else if (wildcard_certificate_match(conn->peer_cn, conn->pghost))
+                       result = true;
+               else if (wildcard_certificate_match(peer_cn, conn->pghost))
                        /* Matched wildcard certificate */
-                       return true;
+                       result = true;
                else
                {
                        printfPQExpBuffer(&conn->errorMessage,
                                                          libpq_gettext("server common name \"%s\" does not match host name \"%s\"\n"),
-                                                         conn->peer_cn, conn->pghost);
-                       return false;
+                                                         peer_cn, conn->pghost);
+                       result = false;
                }
        }
+
+       free(peer_cn);
+       return result;
 }
 
 #ifdef ENABLE_THREAD_SAFETY
@@ -1362,7 +1415,7 @@ open_client_SSL(PGconn *conn)
         * SSL_CTX_set_verify(), if root.crt exists.
         */
 
-       /* pull out server distinguished and common names */
+       /* get server certificate */
        conn->peer = SSL_get_peer_certificate(conn->ssl);
        if (conn->peer == NULL)
        {
@@ -1376,33 +1429,6 @@ open_client_SSL(PGconn *conn)
                return PGRES_POLLING_FAILED;
        }
 
-       X509_NAME_oneline(X509_get_subject_name(conn->peer),
-                                         conn->peer_dn, sizeof(conn->peer_dn));
-       conn->peer_dn[sizeof(conn->peer_dn) - 1] = '\0';
-
-       r = X509_NAME_get_text_by_NID(X509_get_subject_name(conn->peer),
-                                                                 NID_commonName, conn->peer_cn, SM_USER);
-       conn->peer_cn[SM_USER] = '\0';          /* buffer is SM_USER+1 chars! */
-       if (r == -1)
-       {
-               /* Unable to get the CN, set it to blank so it can't be used */
-               conn->peer_cn[0] = '\0';
-       }
-       else
-       {
-               /*
-                * Reject embedded NULLs in certificate common name to prevent attacks
-                * like CVE-2009-4034.
-                */
-               if (r != strlen(conn->peer_cn))
-               {
-                       printfPQExpBuffer(&conn->errorMessage,
-                                                         libpq_gettext("SSL certificate's common name contains embedded null\n"));
-                       close_SSL(conn);
-                       return PGRES_POLLING_FAILED;
-               }
-       }
-
        if (!verify_peer_name_matches_certificate(conn))
        {
                close_SSL(conn);

diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index b968c14a48a334ee7a915d5d1579672f24ec4b06..3cfe5ecd1bf8a4b11a9cc1111676eba502a9376d 100644 (file)
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -397,8 +397,6 @@ struct pg_conn
                                                                 * attempting normal connection */
        SSL                *ssl;                        /* SSL status, if have SSL connection */
        X509       *peer;                       /* X509 cert of server */
-       char            peer_dn[256 + 1];               /* peer distinguished name */
-       char            peer_cn[SM_USER + 1];   /* peer common name */
 #ifdef USE_SSL_ENGINE
        ENGINE     *engine;                     /* SSL engine, if any */
 #else