[PATCH] namespaces: utsname: implement CLONE_NEWUTS flag

Implement a CLONE_NEWUTS flag, and use it at clone and sys_unshare.

[clg@fr.ibm.com: IPC unshare fix]
[bunk@stusta.de: cleanup]
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Cc: Kirill Korotaev <dev@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Andrey Savochkin <saw@sw.ru>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/sched.h

@@ -24,6 +24,7 @@
 #define CLONE_UNTRACED		0x00800000	/* set if the tracing process can't force CLONE_PTRACE on this clone */
 #define CLONE_CHILD_SETTID	0x01000000	/* set the TID in the child */
 #define CLONE_STOPPED		0x02000000	/* Start in stopped state */
+#define CLONE_NEWUTS		0x04000000	/* New utsname group? */
 
 /*
  * Scheduling policies

include/linux/utsname.h

@@ -47,6 +47,8 @@ static inline void get_uts_ns(struct uts_namespace *ns)
 }
 
 #ifdef CONFIG_UTS_NS
+extern int unshare_utsname(unsigned long unshare_flags,
+				struct uts_namespace **new_uts);
 extern int copy_utsname(int flags, struct task_struct *tsk);
 extern void free_uts_ns(struct kref *kref);
 
@@ -55,6 +57,15 @@ static inline void put_uts_ns(struct uts_namespace *ns)
 	kref_put(&ns->kref, free_uts_ns);
 }
 #else
+static inline int unshare_utsname(unsigned long unshare_flags,
+			struct uts_namespace **new_uts)
+{
+	if (unshare_flags & CLONE_NEWUTS)
+		return -EINVAL;
+
+	return 0;
+}
+
 static inline int copy_utsname(int flags, struct task_struct *tsk)
 {
 	return 0;

kernel/fork.c

@@ -1607,13 +1607,14 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 	struct files_struct *fd, *new_fd = NULL;
 	struct sem_undo_list *new_ulist = NULL;
 	struct nsproxy *new_nsproxy, *old_nsproxy;
+	struct uts_namespace *uts, *new_uts = NULL;
 
 	check_unshare_flags(&unshare_flags);
 
 	/* Return -EINVAL for all unsupported flags */
 	err = -EINVAL;
 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
-				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM))
+				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|CLONE_NEWUTS))
 		goto bad_unshare_out;
 
 	if ((err = unshare_thread(unshare_flags)))
@@ -1630,14 +1631,17 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 		goto bad_unshare_cleanup_vm;
 	if ((err = unshare_semundo(unshare_flags, &new_ulist)))
 		goto bad_unshare_cleanup_fd;
+	if ((err = unshare_utsname(unshare_flags, &new_uts)))
+		goto bad_unshare_cleanup_semundo;
 
-	if (new_fs || new_ns || new_sigh || new_mm || new_fd || new_ulist) {
+	if (new_fs || new_ns || new_sigh || new_mm || new_fd || new_ulist ||
+				new_uts) {
 
 		old_nsproxy = current->nsproxy;
 		new_nsproxy = dup_namespaces(old_nsproxy);
 		if (!new_nsproxy) {
 			err = -ENOMEM;
-			goto bad_unshare_cleanup_semundo;
+			goto bad_unshare_cleanup_uts;
 		}
 
 		task_lock(current);
@@ -1676,10 +1680,20 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
 			new_fd = fd;
 		}
 
+		if (new_uts) {
+			uts = current->nsproxy->uts_ns;
+			current->nsproxy->uts_ns = new_uts;
+			new_uts = uts;
+		}
+
 		task_unlock(current);
 		put_nsproxy(old_nsproxy);
 	}
 
+bad_unshare_cleanup_uts:
+	if (new_uts)
+		put_uts_ns(new_uts);
+
 bad_unshare_cleanup_semundo:
 bad_unshare_cleanup_fd:
 	if (new_fd)

kernel/nsproxy.c

@@ -82,7 +82,7 @@ int copy_namespaces(int flags, struct task_struct *tsk)
 
 	get_nsproxy(old_ns);
 
-	if (!(flags & CLONE_NEWNS))
+	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS)))
 		return 0;
 
 	new_ns = clone_namespaces(old_ns);

kernel/utsname.c

@@ -14,6 +14,41 @@
 #include <linux/utsname.h>
 #include <linux/version.h>
 
+/*
+ * Clone a new ns copying an original utsname, setting refcount to 1
+ * @old_ns: namespace to clone
+ * Return NULL on error (failure to kmalloc), new ns otherwise
+ */
+static struct uts_namespace *clone_uts_ns(struct uts_namespace *old_ns)
+{
+	struct uts_namespace *ns;
+
+	ns = kmalloc(sizeof(struct uts_namespace), GFP_KERNEL);
+	if (ns) {
+		memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
+		kref_init(&ns->kref);
+	}
+	return ns;
+}
+
+/*
+ * unshare the current process' utsname namespace.
+ * called only in sys_unshare()
+ */
+int unshare_utsname(unsigned long unshare_flags, struct uts_namespace **new_uts)
+{
+	if (unshare_flags & CLONE_NEWUTS) {
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		*new_uts = clone_uts_ns(current->nsproxy->uts_ns);
+		if (!*new_uts)
+			return -ENOMEM;
+	}
+
+	return 0;
+}
+
 /*
  * Copy task tsk's utsname namespace, or clone it if flags
  * specifies CLONE_NEWUTS.  In latter case, changes to the
@@ -23,6 +58,7 @@
 int copy_utsname(int flags, struct task_struct *tsk)
 {
 	struct uts_namespace *old_ns = tsk->nsproxy->uts_ns;
+	struct uts_namespace *new_ns;
 	int err = 0;
 
 	if (!old_ns)
@@ -30,6 +66,23 @@ int copy_utsname(int flags, struct task_struct *tsk)
 
 	get_uts_ns(old_ns);
 
+	if (!(flags & CLONE_NEWUTS))
+		return 0;
+
+	if (!capable(CAP_SYS_ADMIN)) {
+		err = -EPERM;
+		goto out;
+	}
+
+	new_ns = clone_uts_ns(old_ns);
+	if (!new_ns) {
+		err = -ENOMEM;
+		goto out;
+	}
+	tsk->nsproxy->uts_ns = new_ns;
+
+out:
+	put_uts_ns(old_ns);
 	return err;
 }