Patch "selinux: fix double free in selinux_parse_opts_str()" has been added to the 4.11-stable tree

This is a note to let you know that I've just added the patch titled

selinux: fix double free in selinux_parse_opts_str()

to the 4.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
selinux-fix-double-free-in-selinux_parse_opts_str.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paul Moore <[email protected]>
Date: Wed, 7 Jun 2017 16:48:19 -0400
Subject: selinux: fix double free in selinux_parse_opts_str()

From: Paul Moore <[email protected]>

commit 023f108dcc187e34ef864bf10ed966cf25e14e2a upstream.

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.

---
 security/selinux/hooks.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

@@ -1106,10 +1106,8 @@ static int selinux_parse_opts_str(char *
 
 	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 *
 	return 0;
 
 out_err:
+	security_free_mnt_opts(opts);
 	kfree(context);
 	kfree(defcontext);
 	kfree(fscontext);

Patches currently in stable-queue which might be from [email protected] are

queue-4.11/selinux-fix-double-free-in-selinux_parse_opts_str.patch