ipc: add semtimedop syscall/compat_syscall wrappers

Provide ksys_semtimedop() and compat_ksys_semtimedop() wrappers to avoid
in-kernel calls to these syscalls. The ksys_ prefix denotes that these
functions are meant as a drop-in replacement for the syscalls. In
particular, they use the same calling convention as sys_semtimedop() and
compat_sys_semtimedop().

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
diff --git a/ipc/syscall.c b/ipc/syscall.c
index 3763b42..84d6a76 100644
--- a/ipc/syscall.c
+++ b/ipc/syscall.c
@@ -7,6 +7,9 @@
  */
 #include <linux/unistd.h>
 #include <linux/syscalls.h>
+#include <linux/security.h>
+#include <linux/ipc_namespace.h>
+#include "util.h"
 
 #ifdef __ARCH_WANT_SYS_IPC
 #include <linux/errno.h>
@@ -24,12 +27,12 @@ SYSCALL_DEFINE6(ipc, unsigned int, call, int, first, unsigned long, second,
 
 	switch (call) {
 	case SEMOP:
-		return sys_semtimedop(first, (struct sembuf __user *)ptr,
-				      second, NULL);
+		return ksys_semtimedop(first, (struct sembuf __user *)ptr,
+				       second, NULL);
 	case SEMTIMEDOP:
-		return sys_semtimedop(first, (struct sembuf __user *)ptr,
-				      second,
-				      (const struct timespec __user *)fifth);
+		return ksys_semtimedop(first, (struct sembuf __user *)ptr,
+				       second,
+				       (const struct timespec __user *)fifth);
 
 	case SEMGET:
 		return sys_semget(first, second, third);
@@ -124,9 +127,9 @@ COMPAT_SYSCALL_DEFINE6(ipc, u32, call, int, first, int, second,
 	switch (call) {
 	case SEMOP:
 		/* struct sembuf is the same on 32 and 64bit :)) */
-		return sys_semtimedop(first, compat_ptr(ptr), second, NULL);
+		return ksys_semtimedop(first, compat_ptr(ptr), second, NULL);
 	case SEMTIMEDOP:
-		return compat_sys_semtimedop(first, compat_ptr(ptr), second,
+		return compat_ksys_semtimedop(first, compat_ptr(ptr), second,
 						compat_ptr(fifth));
 	case SEMGET:
 		return sys_semget(first, second, third);