kernel: provide ksys_*() wrappers for syscalls called by kernel/uid16.c

Using these helpers allows us to avoid the in-kernel calls to these
syscalls: sys_setregid(), sys_setgid(), sys_setreuid(), sys_setuid(),
sys_setresuid(), sys_setresgid(), sys_setfsuid(), and sys_setfsgid().

The ksys_ prefix denotes that these function are meant as a drop-in
replacement for the syscall. In particular, they use the same calling
convention.

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: Eric W. Biederman <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

1 files changed, 10 insertions, 9 deletions

diff --git a/kernel/uid16.c b/kernel/uid16.c
index ef1da2a5f9bd..7b930edfe461 100644
--- a/kernel/uid16.c
+++ b/kernel/uid16.c
@@ -18,6 +18,8 @@
 
 #include <linux/uaccess.h>
 
+#include "uid16.h"
+
 SYSCALL_DEFINE3(chown16, const char __user *, filename, old_uid_t, user, old_gid_t, group)
 {
 	return sys_chown(filename, low2highuid(user), low2highgid(group));
@@ -35,27 +37,27 @@ SYSCALL_DEFINE3(fchown16, unsigned int, fd, old_uid_t, user, old_gid_t, group)
 
 SYSCALL_DEFINE2(setregid16, old_gid_t, rgid, old_gid_t, egid)
 {
-	return sys_setregid(low2highgid(rgid), low2highgid(egid));
+	return __sys_setregid(low2highgid(rgid), low2highgid(egid));
 }
 
 SYSCALL_DEFINE1(setgid16, old_gid_t, gid)
 {
-	return sys_setgid(low2highgid(gid));
+	return __sys_setgid(low2highgid(gid));
 }
 
 SYSCALL_DEFINE2(setreuid16, old_uid_t, ruid, old_uid_t, euid)
 {
-	return sys_setreuid(low2highuid(ruid), low2highuid(euid));
+	return __sys_setreuid(low2highuid(ruid), low2highuid(euid));
 }
 
 SYSCALL_DEFINE1(setuid16, old_uid_t, uid)
 {
-	return sys_setuid(low2highuid(uid));
+	return __sys_setuid(low2highuid(uid));
 }
 
 SYSCALL_DEFINE3(setresuid16, old_uid_t, ruid, old_uid_t, euid, old_uid_t, suid)
 {
-	return sys_setresuid(low2highuid(ruid), low2highuid(euid),
+	return __sys_setresuid(low2highuid(ruid), low2highuid(euid),
 				 low2highuid(suid));
 }
 
@@ -78,11 +80,10 @@ SYSCALL_DEFINE3(getresuid16, old_uid_t __user *, ruidp, old_uid_t __user *, euid
 
 SYSCALL_DEFINE3(setresgid16, old_gid_t, rgid, old_gid_t, egid, old_gid_t, sgid)
 {
-	return sys_setresgid(low2highgid(rgid), low2highgid(egid),
+	return __sys_setresgid(low2highgid(rgid), low2highgid(egid),
 				 low2highgid(sgid));
 }
 
-
 SYSCALL_DEFINE3(getresgid16, old_gid_t __user *, rgidp, old_gid_t __user *, egidp, old_gid_t __user *, sgidp)
 {
 	const struct cred *cred = current_cred();
@@ -102,12 +103,12 @@ SYSCALL_DEFINE3(getresgid16, old_gid_t __user *, rgidp, old_gid_t __user *, egid
 
 SYSCALL_DEFINE1(setfsuid16, old_uid_t, uid)
 {
-	return sys_setfsuid(low2highuid(uid));
+	return __sys_setfsuid(low2highuid(uid));
 }
 
 SYSCALL_DEFINE1(setfsgid16, old_gid_t, gid)
 {
-	return sys_setfsgid(low2highgid(gid));
+	return __sys_setfsgid(low2highgid(gid));
 }
 
 static int groups16_to_user(old_gid_t __user *grouplist,