[PATCH] unshare system call -v5: unshare namespace

If the namespace structure is being shared, allocate a new one and copy
information from the current, shared, structure.
Signed-off-by: Janak Desai <janak@us.ibm.com>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Andi Kleen <ak@muc.de>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/namespace.c

@@ -1325,27 +1325,17 @@ dput_out:
 	return retval;
 }
 
-int copy_namespace(int flags, struct task_struct *tsk)
+/*
+ * Allocate a new namespace structure and populate it with contents
+ * copied from the namespace of the passed in task structure.
+ */
+struct namespace *dup_namespace(struct task_struct *tsk, struct fs_struct *fs)
 {
 	struct namespace *namespace = tsk->namespace;
 	struct namespace *new_ns;
 	struct vfsmount *rootmnt = NULL, *pwdmnt = NULL, *altrootmnt = NULL;
-	struct fs_struct *fs = tsk->fs;
 	struct vfsmount *p, *q;
 
-	if (!namespace)
-		return 0;
-
-	get_namespace(namespace);
-
-	if (!(flags & CLONE_NEWNS))
-		return 0;
-
-	if (!capable(CAP_SYS_ADMIN)) {
-		put_namespace(namespace);
-		return -EPERM;
-	}
-
 	new_ns = kmalloc(sizeof(struct namespace), GFP_KERNEL);
 	if (!new_ns)
 		goto out;
@@ -1396,8 +1386,6 @@ int copy_namespace(int flags, struct task_struct *tsk)
 	}
 	up_write(&namespace_sem);
 
-	tsk->namespace = new_ns;
-
 	if (rootmnt)
 		mntput(rootmnt);
 	if (pwdmnt)
@@ -1405,12 +1393,40 @@ int copy_namespace(int flags, struct task_struct *tsk)
 	if (altrootmnt)
 		mntput(altrootmnt);
 
-	put_namespace(namespace);
-	return 0;
+out:
+	return new_ns;
+}
+
+int copy_namespace(int flags, struct task_struct *tsk)
+{
+	struct namespace *namespace = tsk->namespace;
+	struct namespace *new_ns;
+	int err = 0;
+
+	if (!namespace)
+		return 0;
+
+	get_namespace(namespace);
+
+	if (!(flags & CLONE_NEWNS))
+		return 0;
+
+	if (!capable(CAP_SYS_ADMIN)) {
+		err = -EPERM;
+		goto out;
+	}
+
+	new_ns = dup_namespace(tsk, tsk->fs);
+	if (!new_ns) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	tsk->namespace = new_ns;
 
 out:
 	put_namespace(namespace);
-	return -ENOMEM;
+	return err;
 }
 
 asmlinkage long sys_mount(char __user * dev_name, char __user * dir_name,

include/linux/namespace.h

@@ -15,6 +15,7 @@ struct namespace {
 
 extern int copy_namespace(int, struct task_struct *);
 extern void __put_namespace(struct namespace *namespace);
+extern struct namespace *dup_namespace(struct task_struct *, struct fs_struct *);
 
 static inline void put_namespace(struct namespace *namespace)
 {

kernel/fork.c

@@ -1388,16 +1388,21 @@ static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
 }
 
 /*
- * Unsharing of namespace for tasks created without CLONE_NEWNS is not
- * supported yet
+ * Unshare the namespace structure if it is being shared
  */
-static int unshare_namespace(unsigned long unshare_flags, struct namespace **new_nsp)
+static int unshare_namespace(unsigned long unshare_flags, struct namespace **new_nsp, struct fs_struct *new_fs)
 {
 	struct namespace *ns = current->namespace;
 
 	if ((unshare_flags & CLONE_NEWNS) &&
-	    (ns && atomic_read(&ns->count) > 1))
-		return -EINVAL;
+	    (ns && atomic_read(&ns->count) > 1)) {
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		*new_nsp = dup_namespace(current, new_fs ? new_fs : current->fs);
+		if (!*new_nsp)
+			return -ENOMEM;
+	}
 
 	return 0;
 }
@@ -1482,7 +1487,7 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 		goto bad_unshare_out;
 	if ((err = unshare_fs(unshare_flags, &new_fs)))
 		goto bad_unshare_cleanup_thread;
-	if ((err = unshare_namespace(unshare_flags, &new_ns)))
+	if ((err = unshare_namespace(unshare_flags, &new_ns, new_fs)))
 		goto bad_unshare_cleanup_fs;
 	if ((err = unshare_sighand(unshare_flags, &new_sigh)))
 		goto bad_unshare_cleanup_ns;