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 6b1365c6d3efa944952e4410cf17a2360cbff53f..dce0eaa20e208314c14fda855994f071c5831c34 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
@@ -945,44 +946,54 @@ 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);
@@ -1008,6 +1019,12 @@ 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 ad670c3216f66bebb07b98f217dec1c02ca444e0..4d92c18974bc56b402445671e4ff84d7c7628daa 100644 (file)
--- a/src/include/libpq/libpq-be.h
+++ b/src/include/libpq/libpq-be.h
@@ -175,8 +175,7 @@ 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 3c1ca8c97fae2736ecf65479ab6b888f2eab9cb7..5c4d73c3acf4a214185bdf6c49881e050fa74e66 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
@@ -1372,7 +1425,7 @@ 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)
        {
@@ -1386,33 +1439,6 @@ 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 987311efc8dd63d15b1849e13f58770f581af208..2103af88329894d5cecee7f4de0214ab8613bbe4 100644 (file)
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -406,8 +406,6 @@ 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