cifs: fix potential buffer overrun when composing a new options string

Consider the case where we have a very short ip= string in the original
mount options, and when we chase a referral we end up with a very long
IPv6 address. Be sure to allow for that possibility when estimating the
size of the string to allocate.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/fs/cifs/cifs_dfs_ref.c b/fs/cifs/cifs_dfs_ref.c
index 8e33ec65847b..8e5a1817496d 100644
--- a/fs/cifs/cifs_dfs_ref.c
+++ b/fs/cifs/cifs_dfs_ref.c
@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/vfs.h>
 #include <linux/fs.h>
+#include <linux/inet.h>
 #include "cifsglob.h"
 #include "cifsproto.h"
 #include "cifsfs.h"
@@ -150,7 +151,8 @@ char *cifs_compose_mount_options(const char *sb_mountdata,
          * assuming that we have 'unc=' and 'ip=' in
          * the original sb_mountdata
          */
-        md_len = strlen(sb_mountdata) + rc + strlen(ref->node_name) + 12;
+        md_len = strlen(sb_mountdata) + rc + strlen(ref->node_name) + 12 +
+                        INET6_ADDRSTRLEN;
         mountdata = kzalloc(md_len+1, GFP_KERNEL);
         if (mountdata == NULL) {
                 rc = -ENOMEM;