linux-kernel - [PATCH] kernel: user_namespace: always set the return parameter 'new_cred' when call unshare

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Date:	Tue, 20 Aug 2013 10:53:43 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"dhowells@...hat.com" <dhowells@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] kernel: user_namespace: always set the return parameter 'new_cred'
 when call unshare_userns() successfully.

When unshare_userns() succeed, recommend to always set the return
parameter which may be used by caller.

The caller has rights to call it with 'new_cred' uninitialized, if
succeed, the caller can assume the 'new_cred' has been initialized.

Signed-off-by: Chen Gang <gang.chen@...anux.com>
---
 include/linux/user_namespace.h |    1 +
 kernel/user_namespace.c        |    4 +++-
 2 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index b6b215f..3159af5 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -75,6 +75,7 @@ static inline int unshare_userns(unsigned long unshare_flags,
 {
 	if (unshare_flags & CLONE_NEWUSER)
 		return -EINVAL;
+	*new_cred = NULL;
 	return 0;
 }
 
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 6e50a44..6b90818 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -107,8 +107,10 @@ int unshare_userns(unsigned long unshare_flags, struct cred **new_cred)
 	struct cred *cred;
 	int err = -ENOMEM;
 
-	if (!(unshare_flags & CLONE_NEWUSER))
+	if (!(unshare_flags & CLONE_NEWUSER)) {
+		*new_cred = NULL;
 		return 0;
+	}
 
 	cred = prepare_creds();
 	if (cred) {
-- 
1.7.7.6
--
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