userns: allow sethostname in a container

Changelog:
	Feb 23: let clone_uts_ns() handle setting uts->user_ns
		To do so we need to pass in the task_struct who'll
		get the utsname, so we can get its user_ns.
	Feb 23: As per Oleg's coment, just pass in tsk, instead of two
		of its members.

Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: David Howells <dhowells@redhat.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 9 insertions, 12 deletions

diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 034dc2ed13ac..b97fc9d04ddf 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -69,16 +69,11 @@ static struct nsproxy *create_new_namespaces(unsigned long flags,
                 goto out_ns;
         }
 
-        new_nsp->uts_ns = copy_utsname(flags, tsk->nsproxy->uts_ns);
+        new_nsp->uts_ns = copy_utsname(flags, tsk);
         if (IS_ERR(new_nsp->uts_ns)) {
                 err = PTR_ERR(new_nsp->uts_ns);
                 goto out_uts;
         }
-        if (new_nsp->uts_ns != tsk->nsproxy->uts_ns) {
-                put_user_ns(new_nsp->uts_ns->user_ns);
-                new_nsp->uts_ns->user_ns = task_cred_xxx(tsk, user)->user_ns;
-                get_user_ns(new_nsp->uts_ns->user_ns);
-        }
 
         new_nsp->ipc_ns = copy_ipcs(flags, tsk->nsproxy->ipc_ns);
         if (IS_ERR(new_nsp->ipc_ns)) {
diff --git a/kernel/sys.c b/kernel/sys.c
index 1ad48b3b9068..5761c53e19e3 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1181,7 +1181,7 @@ SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
         int errno;
         char tmp[__NEW_UTS_LEN];
 
-        if (!capable(CAP_SYS_ADMIN))
+        if (!ns_capable(current->nsproxy->uts_ns->user_ns, CAP_SYS_ADMIN))
                 return -EPERM;
         if (len < 0 || len > __NEW_UTS_LEN)
                 return -EINVAL;
diff --git a/kernel/utsname.c b/kernel/utsname.c
index a7b3a8d1ad24..44646179eaba 100644
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -31,7 +31,8 @@ static struct uts_namespace *create_uts_ns(void)
  * @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)
+static struct uts_namespace *clone_uts_ns(struct task_struct *tsk,
+                                          struct uts_namespace *old_ns)
 {
         struct uts_namespace *ns;
 
@@ -41,8 +42,7 @@ static struct uts_namespace *clone_uts_ns(struct uts_namespace *old_ns)
 
         down_read(&uts_sem);
         memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
-        ns->user_ns = old_ns->user_ns;
-        get_user_ns(ns->user_ns);
+        ns->user_ns = get_user_ns(task_cred_xxx(tsk, user)->user_ns);
         up_read(&uts_sem);
         return ns;
 }
@@ -53,8 +53,10 @@ static struct uts_namespace *clone_uts_ns(struct uts_namespace *old_ns)
  * utsname of this process won't be seen by parent, and vice
  * versa.
  */
-struct uts_namespace *copy_utsname(unsigned long flags, struct uts_namespace *old_ns)
+struct uts_namespace *copy_utsname(unsigned long flags,
+                                   struct task_struct *tsk)
 {
+        struct uts_namespace *old_ns = tsk->nsproxy->uts_ns;
         struct uts_namespace *new_ns;
 
         BUG_ON(!old_ns);
@@ -63,7 +65,7 @@ struct uts_namespace *copy_utsname(unsigned long flags, struct uts_namespace *ol
         if (!(flags & CLONE_NEWUTS))
                 return old_ns;
 
-        new_ns = clone_uts_ns(old_ns);
+        new_ns = clone_uts_ns(tsk, old_ns);
 
         put_uts_ns(old_ns);
         return new_ns;