ipc: add msgget syscall wrapper

Provide ksys_msgget() wrapper to avoid in-kernel calls to this syscall.
The ksys_ prefix denotes that this function is meant as a drop-in
replacement for the syscall. In particular, it uses the same calling
convention as sys_msgget().

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>

3 files changed, 9 insertions, 3 deletions

diff --git a/ipc/msg.c b/ipc/msg.c
index 0dcc6699dc53..64e8276be164 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -263,7 +263,7 @@ static inline int msg_security(struct kern_ipc_perm *ipcp, int msgflg)
         return security_msg_queue_associate(msq, msgflg);
 }
 
-SYSCALL_DEFINE2(msgget, key_t, key, int, msgflg)
+long ksys_msgget(key_t key, int msgflg)
 {
         struct ipc_namespace *ns;
         static const struct ipc_ops msg_ops = {
@@ -280,6 +280,11 @@ SYSCALL_DEFINE2(msgget, key_t, key, int, msgflg)
         return ipcget(ns, &msg_ids(ns), &msg_ops, &msg_params);
 }
 
+SYSCALL_DEFINE2(msgget, key_t, key, int, msgflg)
+{
+        return ksys_msgget(key, msgflg);
+}
+
 static inline unsigned long
 copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
 {
diff --git a/ipc/syscall.c b/ipc/syscall.c
index a536cca37661..355c4a644bbf 100644
--- a/ipc/syscall.c
+++ b/ipc/syscall.c
@@ -68,7 +68,7 @@ SYSCALL_DEFINE6(ipc, unsigned int, call, int, first, unsigned long, second,
                                            second, fifth, third);
                 }
         case MSGGET:
-                return sys_msgget((key_t) first, second);
+                return ksys_msgget((key_t) first, second);
         case MSGCTL:
                 return sys_msgctl(first, second, (struct msqid_ds __user *)ptr);
 
@@ -161,7 +161,7 @@ COMPAT_SYSCALL_DEFINE6(ipc, u32, call, int, first, int, second,
                 return compat_sys_msgrcv(first, ptr, second, fifth, third);
         }
         case MSGGET:
-                return sys_msgget(first, second);
+                return ksys_msgget(first, second);
         case MSGCTL:
                 return compat_sys_msgctl(first, second, compat_ptr(ptr));
 
diff --git a/ipc/util.h b/ipc/util.h
index 1f1109b83437..b35c0dfe3bc3 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -242,6 +242,7 @@ long ksys_semtimedop(int semid, struct sembuf __user *tsops,
                      const struct timespec __user *timeout);
 long ksys_semget(key_t key, int nsems, int semflg);
 long ksys_semctl(int semid, int semnum, int cmd, unsigned long arg);
+long ksys_msgget(key_t key, int msgflg);
 
 /* for CONFIG_ARCH_WANT_OLD_COMPAT_IPC */
 #ifdef CONFIG_COMPAT