net: socket: move check for forbid_cmsg_compat to __sys_...msg()

The non-compat codepaths for sys_...msg() verify that MSG_CMSG_COMPAT
is not set. By moving this check to the __sys_...msg() functions
(and making it dependent on a static flag passed to this function), we
can call the __sys...msg() functions instead of the syscall functions
in all cases. __sys_recvmmsg() does not need this trickery, as the
check is handled within the do_sys_recvmmsg() function internal to
net/socket.c.

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: David S. Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

1 files changed, 5 insertions, 3 deletions

diff --git a/net/compat.c b/net/compat.c
index f1ec23e9dfce..5caa48987bb2 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -736,19 +736,21 @@ static unsigned char nas[21] = {
 
 COMPAT_SYSCALL_DEFINE3(sendmsg, int, fd, struct compat_msghdr __user *, msg, unsigned int, flags)
 {
-        return __sys_sendmsg(fd, (struct user_msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
+        return __sys_sendmsg(fd, (struct user_msghdr __user *)msg,
+                             flags | MSG_CMSG_COMPAT, false);
 }
 
 COMPAT_SYSCALL_DEFINE4(sendmmsg, int, fd, struct compat_mmsghdr __user *, mmsg,
                        unsigned int, vlen, unsigned int, flags)
 {
         return __sys_sendmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
-                              flags | MSG_CMSG_COMPAT);
+                              flags | MSG_CMSG_COMPAT, false);
 }
 
 COMPAT_SYSCALL_DEFINE3(recvmsg, int, fd, struct compat_msghdr __user *, msg, unsigned int, flags)
 {
-        return __sys_recvmsg(fd, (struct user_msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
+        return __sys_recvmsg(fd, (struct user_msghdr __user *)msg,
+                             flags | MSG_CMSG_COMPAT, false);
 }
 
 COMPAT_SYSCALL_DEFINE4(recv, int, fd, void __user *, buf, compat_size_t, len, unsigned int, flags)