FAILED: patch "[PATCH] selinux: fix double free in selinux_parse_opts_str()" failed to apply to 4.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 023f108dcc187e34ef864bf10ed966cf25e14e2a Mon Sep 17 00:00:00 2001
From: Paul Moore <paul@paul-moore.com>
Date: Wed, 7 Jun 2017 16:48:19 -0400
Subject: [PATCH] selinux: fix double free in selinux_parse_opts_str()

This patch is based on a discussion generated by an earlier patch
from Tetsuo Handa:

* https://marc.info/?t=149035659300001&r=1&w=2

The double free problem involves the mnt_opts field of the
security_mnt_opts struct, selinux_parse_opts_str() frees the memory
on error, but doesn't set the field to NULL so if the caller later
attempts to call security_free_mnt_opts() we trigger the problem.

In order to play it safe we change selinux_parse_opts_str() to call
security_free_mnt_opts() on error instead of free'ing the memory
directly.  This should ensure that everything is handled correctly,
regardless of what the caller may do.

Fixes: e0007529893c1c06 ("LSM/SELinux: Interfaces to allow FS to control mount options")
Cc: stable@vger.kernel.org
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e67a526d1f30..819fd6858b49 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1106,10 +1106,8 @@ static int selinux_parse_opts_str(char *options,
 
 	opts->mnt_opts_flags = kcalloc(NUM_SEL_MNT_OPTS, sizeof(int),
 				       GFP_KERNEL);
-	if (!opts->mnt_opts_flags) {
-		kfree(opts->mnt_opts);
+	if (!opts->mnt_opts_flags)
 		goto out_err;
-	}
 
 	if (fscontext) {
 		opts->mnt_opts[num_mnt_opts] = fscontext;
@@ -1132,6 +1130,7 @@ static int selinux_parse_opts_str(char *options,
 	return 0;
 
 out_err:
+	security_free_mnt_opts(opts);
 	kfree(context);
 	kfree(defcontext);
 	kfree(fscontext);