ipc: add shmget syscall wrapper

Provide ksys_shmget() 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_shmget().

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/shm.c b/ipc/shm.c
index 4643865e9171..9f3cdb259a51 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -656,7 +656,7 @@ static inline int shm_more_checks(struct kern_ipc_perm *ipcp,
         return 0;
 }
 
-SYSCALL_DEFINE3(shmget, key_t, key, size_t, size, int, shmflg)
+long ksys_shmget(key_t key, size_t size, int shmflg)
 {
         struct ipc_namespace *ns;
         static const struct ipc_ops shm_ops = {
@@ -675,6 +675,11 @@ SYSCALL_DEFINE3(shmget, key_t, key, size_t, size, int, shmflg)
         return ipcget(ns, &shm_ids(ns), &shm_ops, &shm_params);
 }
 
+SYSCALL_DEFINE3(shmget, key_t, key, size_t, size, int, shmflg)
+{
+        return ksys_shmget(key, size, shmflg);
+}
+
 static inline unsigned long copy_shmid_to_user(void __user *buf, struct shmid64_ds *in, int version)
 {
         switch (version) {
diff --git a/ipc/syscall.c b/ipc/syscall.c
index 355c4a644bbf..60bceb19b6f0 100644
--- a/ipc/syscall.c
+++ b/ipc/syscall.c
@@ -92,7 +92,7 @@ SYSCALL_DEFINE6(ipc, unsigned int, call, int, first, unsigned long, second,
         case SHMDT:
                 return sys_shmdt((char __user *)ptr);
         case SHMGET:
-                return sys_shmget(first, second, third);
+                return ksys_shmget(first, second, third);
         case SHMCTL:
                 return sys_shmctl(first, second,
                                    (struct shmid_ds __user *) ptr);
@@ -180,7 +180,7 @@ COMPAT_SYSCALL_DEFINE6(ipc, u32, call, int, first, int, second,
         case SHMDT:
                 return sys_shmdt(compat_ptr(ptr));
         case SHMGET:
-                return sys_shmget(first, (unsigned)second, third);
+                return ksys_shmget(first, (unsigned int)second, third);
         case SHMCTL:
                 return compat_sys_shmctl(first, second, compat_ptr(ptr));
         }
diff --git a/ipc/util.h b/ipc/util.h
index b35c0dfe3bc3..51002c0b2a21 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -243,6 +243,7 @@ long ksys_semtimedop(int semid, struct sembuf __user *tsops,
 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);
+long ksys_shmget(key_t key, size_t size, int shmflg);
 
 /* for CONFIG_ARCH_WANT_OLD_COMPAT_IPC */
 #ifdef CONFIG_COMPAT