net: abstract out normal and compat msghdr import

This splits it into two parts, one that imports the message, and one
that imports the iovec. This allows a caller to only do the first part,
and import the iovec manually afterwards.

No functional changes in this patch.
Acked-by: David Miller <davem@davemloft.net>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/socket.h

@@ -391,6 +391,10 @@ extern int recvmsg_copy_msghdr(struct msghdr *msg,
 			       struct user_msghdr __user *umsg, unsigned flags,
 			       struct sockaddr __user **uaddr,
 			       struct iovec **iov);
+extern int __copy_msghdr_from_user(struct msghdr *kmsg,
+				   struct user_msghdr __user *umsg,
+				   struct sockaddr __user **save_addr,
+				   struct iovec __user **uiov, size_t *nsegs);
 
 /* helpers which do the actual work for syscalls */
 extern int __sys_recvfrom(int fd, void __user *ubuf, size_t size,

include/net/compat.h

@@ -38,6 +38,9 @@ struct compat_cmsghdr {
 #define compat_mmsghdr	mmsghdr
 #endif /* defined(CONFIG_COMPAT) */
 
+int __get_compat_msghdr(struct msghdr *kmsg, struct compat_msghdr __user *umsg,
+			struct sockaddr __user **save_addr, compat_uptr_t *ptr,
+			compat_size_t *len);
 int get_compat_msghdr(struct msghdr *, struct compat_msghdr __user *,
 		      struct sockaddr __user **, struct iovec **);
 struct sock_fprog __user *get_compat_bpf_fprog(char __user *optval);

net/compat.c

@@ -33,10 +33,10 @@
 #include <linux/uaccess.h>
 #include <net/compat.h>
 
-int get_compat_msghdr(struct msghdr *kmsg,
+int __get_compat_msghdr(struct msghdr *kmsg,
 			struct compat_msghdr __user *umsg,
 			struct sockaddr __user **save_addr,
-		      struct iovec **iov)
+			compat_uptr_t *ptr, compat_size_t *len)
 {
 	struct compat_msghdr msg;
 	ssize_t err;
@@ -79,10 +79,26 @@ int get_compat_msghdr(struct msghdr *kmsg,
 		return -EMSGSIZE;
 
 	kmsg->msg_iocb = NULL;
+	*ptr = msg.msg_iov;
+	*len = msg.msg_iovlen;
+	return 0;
+}
+
+int get_compat_msghdr(struct msghdr *kmsg,
+		      struct compat_msghdr __user *umsg,
+		      struct sockaddr __user **save_addr,
+		      struct iovec **iov)
+{
+	compat_uptr_t ptr;
+	compat_size_t len;
+	ssize_t err;
+
+	err = __get_compat_msghdr(kmsg, umsg, save_addr, &ptr, &len);
+	if (err)
+		return err;
 
-	err = compat_import_iovec(save_addr ? READ : WRITE,
-				   compat_ptr(msg.msg_iov), msg.msg_iovlen,
-				   UIO_FASTIOV, iov, &kmsg->msg_iter);
+	err = compat_import_iovec(save_addr ? READ : WRITE, compat_ptr(ptr),
+				   len, UIO_FASTIOV, iov, &kmsg->msg_iter);
 	return err < 0 ? err : 0;
 }
 

net/socket.c

@@ -2226,10 +2226,10 @@ struct used_address {
 	unsigned int name_len;
 };
 
-static int copy_msghdr_from_user(struct msghdr *kmsg,
+int __copy_msghdr_from_user(struct msghdr *kmsg,
 			    struct user_msghdr __user *umsg,
 			    struct sockaddr __user **save_addr,
-				 struct iovec **iov)
+			    struct iovec __user **uiov, size_t *nsegs)
 {
 	struct user_msghdr msg;
 	ssize_t err;
@@ -2271,6 +2271,23 @@ static int copy_msghdr_from_user(struct msghdr *kmsg,
 		return -EMSGSIZE;
 
 	kmsg->msg_iocb = NULL;
+	*uiov = msg.msg_iov;
+	*nsegs = msg.msg_iovlen;
+	return 0;
+}
+
+static int copy_msghdr_from_user(struct msghdr *kmsg,
+				 struct user_msghdr __user *umsg,
+				 struct sockaddr __user **save_addr,
+				 struct iovec **iov)
+{
+	struct user_msghdr msg;
+	ssize_t err;
+
+	err = __copy_msghdr_from_user(kmsg, umsg, save_addr, &msg.msg_iov,
+					&msg.msg_iovlen);
+	if (err)
+		return err;
 
 	err = import_iovec(save_addr ? READ : WRITE,
 			    msg.msg_iov, msg.msg_iovlen,