[Devel] [PATCH 2/3] user_ns: bugfix and cleanup

[Serge E. Hallyn]

From: Serge E. Hallyn <serue at us.ibm.com>
Subject: [PATCH 2/3] user_ns: bugfix and cleanup

The first two updates are used in the next patchset:

1. change get_user_ns to return the namespace
2. change get_user_ns and put_user_ns to handle NULL input

This fixes a bug in the lxc patchset:

3. when clone_mnt uses the user_ns from the original vfsmnt (for
   MNT_PRIV_USERNS mounts), it needs to put the user_ns which was
   gotten in alloc_mnt, and get the new one.

Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>
---
 fs/namespace.c                 |    9 +++++----
 include/linux/user_namespace.h |   11 +++++++----
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 55fcaa7..fa52e24 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -57,8 +57,7 @@ struct vfsmount *alloc_vfsmnt(const char
 	struct vfsmount *mnt = kmem_cache_alloc(mnt_cache, GFP_KERNEL);
 	if (mnt) {
 		memset(mnt, 0, sizeof(struct vfsmount));
-		mnt->mnt_user_ns = current->nsproxy->user_ns;
-		get_user_ns(mnt->mnt_user_ns);
+		mnt->mnt_user_ns = get_user_ns(current->nsproxy->user_ns);
 		atomic_set(&mnt->mnt_count, 1);
 		atomic_set(&mnt->mnt_writers, 0);
 		INIT_LIST_HEAD(&mnt->mnt_hash);
@@ -261,8 +260,10 @@ static struct vfsmount *clone_mnt(struct
 
 	if (mnt) {
 		mnt->mnt_flags = old->mnt_flags;
-		if (mnt->mnt_flags & MNT_PRIV_USERNS)
-			mnt->mnt_user_ns = old->mnt_user_ns;
+		if (mnt->mnt_flags & MNT_PRIV_USERNS) {
+			put_user_ns(mnt->mnt_user_ns);
+			mnt->mnt_user_ns = get_user_ns(old->mnt_user_ns);
+		}
 		atomic_inc(&sb->s_active);
 		mnt->mnt_sb = sb;
 		mnt->mnt_root = dget(root);
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index f25c54c..f9d76de 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -17,9 +17,11 @@ extern struct user_namespace init_user_n
 
 #ifdef CONFIG_USER_NS
 
-static inline void get_user_ns(struct user_namespace *ns)
+static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
 {
-	kref_get(&ns->kref);
+	if (ns)
+		kref_get(&ns->kref);
+	return ns;
 }
 
 extern int unshare_user_ns(unsigned long unshare_flags,
@@ -29,12 +31,13 @@ extern void free_user_ns(struct kref *kr
 
 static inline void put_user_ns(struct user_namespace *ns)
 {
-	kref_put(&ns->kref, free_user_ns);
+	if (ns)
+		kref_put(&ns->kref, free_user_ns);
 }
 
 #else
 
-static inline void get_user_ns(struct user_namespace *ns)
+static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
 {
 }
 
-- 
1.4.1

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