[Devel] [PATCH 2/6] user namespace : add unshare

[Serge E. Hallyn]

>From nobody Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <serue at us.ibm.com>
Date: Thu, 5 Apr 2007 13:00:47 -0400
Subject: [PATCH 2/6] user namespace : add unshare

Changelog: Fix !CONFIG_USER_NS clone with CLONE_NEWUSER so it returns -EINVAL
	rather than 0, so that userspace knows they didn't get a new user
	namespace.

Cc: Serge E. Hallyn <serue at us.ibm.com>
Cc: Herbert Poetzl <herbert at 13thfloor.at>
Cc: Kirill Korotaev <dev at sw.ru>
Cc: "Eric W. Biederman" <ebiederm at xmission.com>
Signed-off-by: Andrew Morton <akpm at osdl.org>

Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>

---

 include/linux/sched.h          |    1 +
 include/linux/user_namespace.h |    5 +++-
 kernel/fork.c                  |    2 +-
 kernel/nsproxy.c               |   10 +++++++--
 kernel/user_namespace.c        |   46 +++++++++++++++++++++++++++++++++++++++-
 5 files changed, 59 insertions(+), 5 deletions(-)

4ddd1e8f0539d843e998ea26d0c6c9cb751cbf3e
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 259d0a5..ad19efa 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -26,6 +26,7 @@ #define CLONE_CHILD_SETTID	0x01000000	/*
 #define CLONE_STOPPED		0x02000000	/* Start in stopped state */
 #define CLONE_NEWUTS		0x04000000	/* New utsname group? */
 #define CLONE_NEWIPC		0x08000000	/* New ipcs */
+#define CLONE_NEWUSER		0x10000000	/* New user namespace */
 
 /*
  * Scheduling policies
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index c2debd8..9044456 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -45,7 +45,10 @@ static inline struct user_namespace *get
 static inline struct user_namespace *copy_user_ns(int flags,
 						  struct user_namespace *old_ns)
 {
-	return 0;
+	if (flags & CLONE_NEWUSER)
+		return ERR_PTR(-EINVAL);
+
+	return NULL;
 }
 
 static inline void put_user_ns(struct user_namespace *ns)
diff --git a/kernel/fork.c b/kernel/fork.c
index c20137e..123bc93 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1581,7 +1581,7 @@ asmlinkage long sys_unshare(unsigned lon
 	err = -EINVAL;
 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
-				CLONE_NEWUTS|CLONE_NEWIPC))
+				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER))
 		goto bad_unshare_out;
 
 	if ((err = unshare_thread(unshare_flags)))
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 1ea8a73..fb00706 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -121,7 +121,7 @@ int copy_namespaces(int flags, struct ta
 
 	get_nsproxy(old_ns);
 
-	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC)))
+	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWUSER)))
 		return 0;
 
 	if (!capable(CAP_SYS_ADMIN)) {
@@ -168,9 +168,15 @@ int unshare_nsproxy_namespaces(unsigned 
 	struct nsproxy *old_ns = current->nsproxy;
 	int err = 0;
 
-	if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC)))
+	if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
+			       CLONE_NEWUSER)))
 		return 0;
 
+#ifndef CONFIG_USER_NS
+	if (unshare_flags & CLONE_NEWUSER)
+		return -EINVAL;
+#endif
+
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 3d79642..89a27e8 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -21,6 +21,45 @@ EXPORT_SYMBOL_GPL(init_user_ns);
 
 #ifdef CONFIG_USER_NS
 
+/*
+ * Clone a new ns copying an original user ns, setting refcount to 1
+ * @old_ns: namespace to clone
+ * Return NULL on error (failure to kmalloc), new ns otherwise
+ */
+static struct user_namespace *clone_user_ns(struct user_namespace *old_ns)
+{
+	struct user_namespace *ns;
+	struct user_struct *new_user;
+	int n;
+
+	ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);
+	if (!ns)
+		return NULL;
+
+	kref_init(&ns->kref);
+
+	for (n = 0; n < UIDHASH_SZ; ++n)
+		INIT_LIST_HEAD(ns->uidhash_table + n);
+
+	/* Insert new root user.  */
+	ns->root_user = alloc_uid(ns, 0);
+	if (!ns->root_user) {
+		kfree(ns);
+		return NULL;
+	}
+
+	/* Reset current->user with a new one */
+	new_user = alloc_uid(ns, current->uid);
+	if (!new_user) {
+		free_uid(ns->root_user);
+		kfree(ns);
+		return NULL;
+	}
+
+	switch_uid(new_user);
+	return ns;
+}
+
 struct user_namespace * copy_user_ns(int flags, struct user_namespace *old_ns)
 {
 	struct user_namespace *new_ns;
@@ -28,7 +67,12 @@ struct user_namespace * copy_user_ns(int
 	BUG_ON(!old_ns);
 	get_user_ns(old_ns);
 
-	new_ns = old_ns;
+	if (!(flags & CLONE_NEWUSER))
+		return old_ns;
+
+	new_ns = clone_user_ns(old_ns);
+
+	put_user_ns(old_ns);
 	return new_ns;
 }
 
-- 
1.3.2