net: Unbreak compat_sys_{send,recv}msg

I broke them in this commit:

    commit 1be374a0
    Author: Andy Lutomirski <luto@amacapital.net>
    Date:   Wed May 22 14:07:44 2013 -0700

        net: Block MSG_CMSG_COMPAT in send(m)msg and recv(m)msg

This patch adds __sys_sendmsg and __sys_sendmsg as common helpers that accept
MSG_CMSG_COMPAT and blocks MSG_CMSG_COMPAT at the syscall entrypoints.  It
also reverts some unnecessary checks in sys_socketcall.

Apparently I was suffering from underscore blindness the first time around.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Tested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/socket.h

@@ -320,6 +320,9 @@ extern int put_cmsg(struct msghdr*, int level, int type, int len, void *data);
 
 struct timespec;
 
+/* The __sys_...msg variants allow MSG_CMSG_COMPAT */
+extern long __sys_recvmsg(int fd, struct msghdr __user *msg, unsigned flags);
+extern long __sys_sendmsg(int fd, struct msghdr __user *msg, unsigned flags);
 extern int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
 			  unsigned int flags, struct timespec *timeout);
 extern int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg,

net/compat.c

@@ -734,19 +734,25 @@ static unsigned char nas[21] = {
 
 asmlinkage long compat_sys_sendmsg(int fd, struct compat_msghdr __user *msg, unsigned int flags)
 {
-	return sys_sendmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
+	if (flags & MSG_CMSG_COMPAT)
+		return -EINVAL;
+	return __sys_sendmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
 }
 
 asmlinkage long compat_sys_sendmmsg(int fd, struct compat_mmsghdr __user *mmsg,
 				    unsigned int vlen, unsigned int flags)
 {
+	if (flags & MSG_CMSG_COMPAT)
+		return -EINVAL;
 	return __sys_sendmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
 			      flags | MSG_CMSG_COMPAT);
 }
 
 asmlinkage long compat_sys_recvmsg(int fd, struct compat_msghdr __user *msg, unsigned int flags)
 {
-	return sys_recvmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
+	if (flags & MSG_CMSG_COMPAT)
+		return -EINVAL;
+	return __sys_recvmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
 }
 
 asmlinkage long compat_sys_recv(int fd, void __user *buf, size_t len, unsigned int flags)
@@ -768,6 +774,9 @@ asmlinkage long compat_sys_recvmmsg(int fd, struct compat_mmsghdr __user *mmsg,
 	int datagrams;
 	struct timespec ktspec;
 
+	if (flags & MSG_CMSG_COMPAT)
+		return -EINVAL;
+
 	if (COMPAT_USE_64BIT_TIME)
 		return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
 				      flags | MSG_CMSG_COMPAT,

net/socket.c

@@ -1956,7 +1956,7 @@ struct used_address {
 	unsigned int name_len;
 };
 
-static int __sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
+static int ___sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
 			 struct msghdr *msg_sys, unsigned int flags,
 			 struct used_address *used_address)
 {
@@ -2071,26 +2071,30 @@ static int __sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
  *	BSD sendmsg interface
  */
 
-SYSCALL_DEFINE3(sendmsg, int, fd, struct msghdr __user *, msg, unsigned int, flags)
+long __sys_sendmsg(int fd, struct msghdr __user *msg, unsigned flags)
 {
 	int fput_needed, err;
 	struct msghdr msg_sys;
 	struct socket *sock;
 
-	if (flags & MSG_CMSG_COMPAT)
-		return -EINVAL;
-
 	sock = sockfd_lookup_light(fd, &err, &fput_needed);
 	if (!sock)
 		goto out;
 
-	err = __sys_sendmsg(sock, msg, &msg_sys, flags, NULL);
+	err = ___sys_sendmsg(sock, msg, &msg_sys, flags, NULL);
 
 	fput_light(sock->file, fput_needed);
 out:
 	return err;
 }
 
+SYSCALL_DEFINE3(sendmsg, int, fd, struct msghdr __user *, msg, unsigned int, flags)
+{
+	if (flags & MSG_CMSG_COMPAT)
+		return -EINVAL;
+	return __sys_sendmsg(fd, msg, flags);
+}
+
 /*
  *	Linux sendmmsg interface
  */
@@ -2121,15 +2125,16 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
 
 	while (datagrams < vlen) {
 		if (MSG_CMSG_COMPAT & flags) {
-			err = __sys_sendmsg(sock, (struct msghdr __user *)compat_entry,
-					    &msg_sys, flags, &used_address);
+			err = ___sys_sendmsg(sock, (struct msghdr __user *)compat_entry,
+					     &msg_sys, flags, &used_address);
 			if (err < 0)
 				break;
 			err = __put_user(err, &compat_entry->msg_len);
 			++compat_entry;
 		} else {
-			err = __sys_sendmsg(sock, (struct msghdr __user *)entry,
-					    &msg_sys, flags, &used_address);
+			err = ___sys_sendmsg(sock,
+					     (struct msghdr __user *)entry,
+					     &msg_sys, flags, &used_address);
 			if (err < 0)
 				break;
 			err = put_user(err, &entry->msg_len);
@@ -2158,7 +2163,7 @@ SYSCALL_DEFINE4(sendmmsg, int, fd, struct mmsghdr __user *, mmsg,
 	return __sys_sendmmsg(fd, mmsg, vlen, flags);
 }
 
-static int __sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
+static int ___sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
 			 struct msghdr *msg_sys, unsigned int flags, int nosec)
 {
 	struct compat_msghdr __user *msg_compat =
@@ -2250,27 +2255,31 @@ static int __sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
  *	BSD recvmsg interface
  */
 
-SYSCALL_DEFINE3(recvmsg, int, fd, struct msghdr __user *, msg,
-		unsigned int, flags)
+long __sys_recvmsg(int fd, struct msghdr __user *msg, unsigned flags)
 {
 	int fput_needed, err;
 	struct msghdr msg_sys;
 	struct socket *sock;
 
-	if (flags & MSG_CMSG_COMPAT)
-		return -EINVAL;
-
 	sock = sockfd_lookup_light(fd, &err, &fput_needed);
 	if (!sock)
 		goto out;
 
-	err = __sys_recvmsg(sock, msg, &msg_sys, flags, 0);
+	err = ___sys_recvmsg(sock, msg, &msg_sys, flags, 0);
 
 	fput_light(sock->file, fput_needed);
 out:
 	return err;
 }
 
+SYSCALL_DEFINE3(recvmsg, int, fd, struct msghdr __user *, msg,
+		unsigned int, flags)
+{
+	if (flags & MSG_CMSG_COMPAT)
+		return -EINVAL;
+	return __sys_recvmsg(fd, msg, flags);
+}
+
 /*
  *     Linux recvmmsg interface
  */
@@ -2308,17 +2317,18 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
 		 * No need to ask LSM for more than the first datagram.
 		 */
 		if (MSG_CMSG_COMPAT & flags) {
-			err = __sys_recvmsg(sock, (struct msghdr __user *)compat_entry,
-					    &msg_sys, flags & ~MSG_WAITFORONE,
-					    datagrams);
+			err = ___sys_recvmsg(sock, (struct msghdr __user *)compat_entry,
+					     &msg_sys, flags & ~MSG_WAITFORONE,
+					     datagrams);
 			if (err < 0)
 				break;
 			err = __put_user(err, &compat_entry->msg_len);
 			++compat_entry;
 		} else {
-			err = __sys_recvmsg(sock, (struct msghdr __user *)entry,
-					    &msg_sys, flags & ~MSG_WAITFORONE,
-					    datagrams);
+			err = ___sys_recvmsg(sock,
+					     (struct msghdr __user *)entry,
+					     &msg_sys, flags & ~MSG_WAITFORONE,
+					     datagrams);
 			if (err < 0)
 				break;
 			err = put_user(err, &entry->msg_len);
@@ -2505,31 +2515,15 @@ SYSCALL_DEFINE2(socketcall, int, call, unsigned long __user *, args)
 				   (int __user *)a[4]);
 		break;
 	case SYS_SENDMSG:
-		if (a[2] & MSG_CMSG_COMPAT) {
-			err = -EINVAL;
-			break;
-		}
 		err = sys_sendmsg(a0, (struct msghdr __user *)a1, a[2]);
 		break;
 	case SYS_SENDMMSG:
-		if (a[3] & MSG_CMSG_COMPAT) {
-			err = -EINVAL;
-			break;
-		}
 		err = sys_sendmmsg(a0, (struct mmsghdr __user *)a1, a[2], a[3]);
 		break;
 	case SYS_RECVMSG:
-		if (a[2] & MSG_CMSG_COMPAT) {
-			err = -EINVAL;
-			break;
-		}
 		err = sys_recvmsg(a0, (struct msghdr __user *)a1, a[2]);
 		break;
 	case SYS_RECVMMSG:
-		if (a[3] & MSG_CMSG_COMPAT) {
-			err = -EINVAL;
-			break;
-		}
 		err = sys_recvmmsg(a0, (struct mmsghdr __user *)a1, a[2], a[3],
 				   (struct timespec __user *)a[4]);
 		break;