signal: simplify rt_sigaction()

The goto is not needed and does not add any clarity.  Simply return
-EINVAL on unexpected sigset_t struct size directly.

Link: http://lkml.kernel.org/r/20180602103653.18181-6-christian@brauner.io
Signed-off-by: Christian Brauner <christian@brauner.io>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Morris <james.morris@microsoft.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/signal.c

@@ -3648,25 +3648,23 @@ SYSCALL_DEFINE4(rt_sigaction, int, sig,
 		size_t, sigsetsize)
 {
 	struct k_sigaction new_sa, old_sa;
-	int ret = -EINVAL;
+	int ret;
 
 	/* XXX: Don't preclude handling different sized sigset_t's.  */
 	if (sigsetsize != sizeof(sigset_t))
-		goto out;
+		return -EINVAL;
 
-	if (act) {
-		if (copy_from_user(&new_sa.sa, act, sizeof(new_sa.sa)))
-			return -EFAULT;
-	}
+	if (act && copy_from_user(&new_sa.sa, act, sizeof(new_sa.sa)))
+		return -EFAULT;
 
 	ret = do_sigaction(sig, act ? &new_sa : NULL, oact ? &old_sa : NULL);
+	if (ret)
+		return ret;
 
-	if (!ret && oact) {
-		if (copy_to_user(oact, &old_sa.sa, sizeof(old_sa.sa)))
-			return -EFAULT;
-	}
-out:
-	return ret;
+	if (oact && copy_to_user(oact, &old_sa.sa, sizeof(old_sa.sa)))
+		return -EFAULT;
+
+	return 0;
 }
 #ifdef CONFIG_COMPAT
 COMPAT_SYSCALL_DEFINE4(rt_sigaction, int, sig,