Fix UTS corruption during clone(CLONE_NEWUTS)

struct utsname is copied from master one without any exclusion.

Here is sample output from one proggie doing

	sethostname("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa");
	sethostname("bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb");

and another

	clone(,, CLONE_NEWUTS, ...)
	uname()

	hostname = 'aaaaaaaaaaaaaaaaaaaaaaaaabbbbb'
	hostname = 'bbbaaaaaaaaaaaaaaaaaaaaaaaaaaa'
	hostname = 'aaaaaaaabbbbbbbbbbbbbbbbbbbbbb'
	hostname = 'aaaaaaaaaaaaaaaaaaaaaaaaaabbbb'
	hostname = 'aaaaaaaaaaaaaaaaaaaaaaaaaaaabb'
	hostname = 'aaabbbbbbbbbbbbbbbbbbbbbbbbbbb'
	hostname = 'bbbbbbbbbbbbbbbbaaaaaaaaaaaaaa'

Hostname is sometimes corrupted.

Yes, even _the_ simplest namespace activity had bug in it. :-(
Signed-off-by: NAlexey Dobriyan <adobriyan@sw.ru>
Acked-by: NSerge Hallyn <serue@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/utsname.c

@@ -28,7 +28,9 @@ static struct uts_namespace *clone_uts_ns(struct uts_namespace *old_ns)
 	if (!ns)
 		return ERR_PTR(-ENOMEM);
 
+	down_read(&uts_sem);
 	memcpy(&ns->name, &old_ns->name, sizeof(ns->name));
+	up_read(&uts_sem);
 	kref_init(&ns->kref);
 	return ns;
 }