CVE-2014-0210: unvalidated length in _fs_recv_conn_setup()

The connection setup reply from the font server can include a list
of alternate servers to contact if this font server stops working.

The reply specifies a total size of all the font server names, and
then provides a list of names. _fs_recv_conn_setup() allocated the
specified total size for copying the names to, but didn't check to
make sure it wasn't copying more data to that buffer than the size
it had allocated.

Reported-by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Matthieu Herrb <matthieu@herrb.eu>

1 files changed, 18 insertions, 2 deletions

diff --git a/src/fc/fserve.c b/src/fc/fserve.c
index 3585951..aa9acdb 100644
--- a/src/fc/fserve.c
+++ b/src/fc/fserve.c
@@ -2784,7 +2784,7 @@ _fs_recv_conn_setup (FSFpePtr conn)
     int			ret = FSIO_ERROR;
     fsConnSetup		*setup;
     FSFpeAltPtr		alts;
-    int			i, alt_len;
+    unsigned int	i, alt_len;
     int			setup_len;
     char		*alt_save, *alt_names;
 
@@ -2811,8 +2811,9 @@ _fs_recv_conn_setup (FSFpePtr conn)
 	}
 	if (setup->num_alternates)
 	{
+	    size_t alt_name_len = setup->alternate_len << 2;
 	    alts = malloc (setup->num_alternates * sizeof (FSFpeAltRec) +
-			   (setup->alternate_len << 2));
+			   alt_name_len);
 	    if (alts)
 	    {
 		alt_names = (char *) (setup + 1);
@@ -2821,10 +2822,25 @@ _fs_recv_conn_setup (FSFpePtr conn)
 		{
 		    alts[i].subset = alt_names[0];
 		    alt_len = alt_names[1];
+		    if (alt_len >= alt_name_len) {
+			/*
+			 * Length is longer than setup->alternate_len
+			 * told us to allocate room for, assume entire
+			 * alternate list is corrupted.
+			 */
+#ifdef DEBUG
+			fprintf (stderr,
+				 "invalid alt list (length %lx >= %lx)\n",
+				 (long) alt_len, (long) alt_name_len);
+#endif
+			free(alts);
+			return FSIO_ERROR;
+		    }
 		    alts[i].name = alt_save;
 		    memcpy (alt_save, alt_names + 2, alt_len);
 		    alt_save[alt_len] = '\0';
 		    alt_save += alt_len + 1;
+		    alt_name_len -= alt_len + 1;
 		    alt_names += _fs_pad_length (alt_len + 2);
 		}
 		conn->numAlts = setup->num_alternates;