[ 3.8.y.z extended stable ] Patch "userns: unshare_userns(&cred) should not populate cred on failure" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    userns: unshare_userns(&cred) should not populate cred on failure

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.7.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From cd9c7111df7579e703cebf039082c115c0de4471 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg at redhat.com>
Date: Tue, 6 Aug 2013 19:38:55 +0200
Subject: userns: unshare_userns(&cred) should not populate cred on failure

commit 6160968cee8b90a5dd95318d716e31d7775c4ef3 upstream.

unshare_userns(new_cred) does *new_cred = prepare_creds() before
create_user_ns() which can fail. However, the caller expects that
it doesn't need to take care of new_cred if unshare_userns() fails.

We could change the single caller, sys_unshare(), but I think it
would be more clean to avoid the side effects on failure, so with
this patch unshare_userns() does put_cred() itself and initializes
*new_cred only if create_user_ns() succeeeds.

Signed-off-by: Oleg Nesterov <oleg at redhat.com>
Reviewed-by: Andy Lutomirski <luto at amacapital.net>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/user_namespace.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index f359dc7..38ae0f5 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -105,16 +105,21 @@ int create_user_ns(struct cred *new)
 int unshare_userns(unsigned long unshare_flags, struct cred **new_cred)
 {
 	struct cred *cred;
+	int err = -ENOMEM;

 	if (!(unshare_flags & CLONE_NEWUSER))
 		return 0;

 	cred = prepare_creds();
-	if (!cred)
-		return -ENOMEM;
+	if (cred) {
+		err = create_user_ns(cred);
+		if (err)
+			put_cred(cred);
+		else
+			*new_cred = cred;
+	}

-	*new_cred = cred;
-	return create_user_ns(cred);
+	return err;
 }

 void free_user_ns(struct kref *kref)
--
1.8.1.2