[CIFS] Fix oops in cifs_strfromUCS_le mounting to servers which do not specify their OS

Fixes kernel bug #10451 http://bugzilla.kernel.org/show_bug.cgi?id=10451

Certain NAS appliances do not set the operating system or network operating system
fields in the session setup response on the wire.  cifs was oopsing on the unexpected
zero length response fields (when trying to null terminate a zero length field).

This fixes the oops.
Acked-by: NJeff Layton <jlayton@redhat.com>
CC: stable <stable@kernel.org>
Signed-off-by: NSteve French <sfrench@us.ibm.com>

fs/cifs/CHANGES

@@ -7,7 +7,8 @@ specified and user does not have access to query information about the
 top of the share.  Fix problem in 2.6.28 resolving DFS paths to
 Samba servers (worked to Windows).  Fix rmdir so that pending search
 (readdir) requests do not get invalid results which include the now
-removed directory.
+removed directory.  Fix oops in cifs_dfs_ref.c when prefixpath is not reachable
+when using DFS.
 
 Version 1.55
 ------------

fs/cifs/sess.c

@@ -228,7 +228,7 @@ static int decode_unicode_ssetup(char **pbcc_area, int bleft,
 
 	kfree(ses->serverOS);
 	/* UTF-8 string will not grow more than four times as big as UCS-16 */
-	ses->serverOS = kzalloc(4 * len, GFP_KERNEL);
+	ses->serverOS = kzalloc((4 * len) + 2 /* trailing null */, GFP_KERNEL);
 	if (ses->serverOS != NULL)
 		cifs_strfromUCS_le(ses->serverOS, (__le16 *)data, len, nls_cp);
 	data += 2 * (len + 1);
@@ -241,7 +241,7 @@ static int decode_unicode_ssetup(char **pbcc_area, int bleft,
 		return rc;
 
 	kfree(ses->serverNOS);
-	ses->serverNOS = kzalloc(4 * len, GFP_KERNEL); /* BB this is wrong length FIXME BB */
+	ses->serverNOS = kzalloc((4 * len) + 2 /* trailing null */, GFP_KERNEL);
 	if (ses->serverNOS != NULL) {
 		cifs_strfromUCS_le(ses->serverNOS, (__le16 *)data, len,
 				   nls_cp);