[PATCH for-next 2/3] net: copy from user before calling __get_compat_msghdr

[Dylan Yudaken <dylany@fb.com>]

this is in preparation for multishot receive from io_uring, where it needs
to have access to the original struct user_msghdr.

functionally this should be a no-op.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
---
 include/net/compat.h |  5 ++---
 io_uring/net.c       | 17 +++++++++--------
 net/compat.c         | 39 +++++++++++++++++----------------------
 3 files changed, 28 insertions(+), 33 deletions(-)

diff --git a/include/net/compat.h b/include/net/compat.h
index 595fee069b82..84c163f40f38 100644
--- a/include/net/compat.h
+++ b/include/net/compat.h
@@ -46,9 +46,8 @@ struct compat_rtentry {
 	unsigned short  rt_irtt;        /* Initial RTT                  */
 };
 
-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 *kmsg, struct compat_msghdr *msg,
+			struct sockaddr __user **save_addr);
 int get_compat_msghdr(struct msghdr *, struct compat_msghdr __user *,
 		      struct sockaddr __user **, struct iovec **);
 int put_cmsg_compat(struct msghdr*, int, int, int, void *);
diff --git a/io_uring/net.c b/io_uring/net.c
index 99fb878afd65..e2875c114adc 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -370,24 +370,25 @@ static int __io_compat_recvmsg_copy_hdr(struct io_kiocb *req,
 					struct io_async_msghdr *iomsg)
 {
 	struct io_sr_msg *sr = io_kiocb_to_cmd(req);
+	struct compat_msghdr msg;
 	struct compat_iovec __user *uiov;
-	compat_uptr_t ptr;
-	compat_size_t len;
 	int ret;
 
-	ret = __get_compat_msghdr(&iomsg->msg, sr->umsg_compat, &iomsg->uaddr,
-				  &ptr, &len);
+	if (copy_from_user(&msg, sr->umsg_compat, sizeof(msg)))
+		return -EFAULT;
+
+	ret = __get_compat_msghdr(&iomsg->msg, sr->umsg_compat, &iomsg->uaddr);
 	if (ret)
 		return ret;
 
-	uiov = compat_ptr(ptr);
+	uiov = compat_ptr(msg.msg_iov);
 	if (req->flags & REQ_F_BUFFER_SELECT) {
 		compat_ssize_t clen;
 
-		if (len == 0) {
+		if (msg.msg_iovlen == 0) {
 			sr->len = 0;
 			iomsg->free_iov = NULL;
-		} else if (len > 1) {
+		} else if (msg.msg_iovlen > 1) {
 			return -EINVAL;
 		} else {
 			if (!access_ok(uiov, sizeof(*uiov)))
@@ -401,7 +402,7 @@ static int __io_compat_recvmsg_copy_hdr(struct io_kiocb *req,
 		}
 	} else {
 		iomsg->free_iov = iomsg->fast_iov;
-		ret = __import_iovec(READ, (struct iovec __user *)uiov, len,
+		ret = __import_iovec(READ, (struct iovec __user *)uiov, msg.msg_iovlen,
 				   UIO_FASTIOV, &iomsg->free_iov,
 				   &iomsg->msg.msg_iter, true);
 		if (ret < 0)
diff --git a/net/compat.c b/net/compat.c
index 210fc3b4d0d8..513aa9a3fc64 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -34,20 +34,15 @@
 #include <net/compat.h>
 
 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)
+			struct compat_msghdr *msg,
+			struct sockaddr __user **save_addr)
 {
-	struct compat_msghdr msg;
 	ssize_t err;
 
-	if (copy_from_user(&msg, umsg, sizeof(*umsg)))
-		return -EFAULT;
-
-	kmsg->msg_flags = msg.msg_flags;
-	kmsg->msg_namelen = msg.msg_namelen;
+	kmsg->msg_flags = msg->msg_flags;
+	kmsg->msg_namelen = msg->msg_namelen;
 
-	if (!msg.msg_name)
+	if (!msg->msg_name)
 		kmsg->msg_namelen = 0;
 
 	if (kmsg->msg_namelen < 0)
@@ -57,15 +52,15 @@ int __get_compat_msghdr(struct msghdr *kmsg,
 		kmsg->msg_namelen = sizeof(struct sockaddr_storage);
 
 	kmsg->msg_control_is_user = true;
-	kmsg->msg_control_user = compat_ptr(msg.msg_control);
-	kmsg->msg_controllen = msg.msg_controllen;
+	kmsg->msg_control_user = compat_ptr(msg->msg_control);
+	kmsg->msg_controllen = msg->msg_controllen;
 
 	if (save_addr)
-		*save_addr = compat_ptr(msg.msg_name);
+		*save_addr = compat_ptr(msg->msg_name);
 
-	if (msg.msg_name && kmsg->msg_namelen) {
+	if (msg->msg_name && kmsg->msg_namelen) {
 		if (!save_addr) {
-			err = move_addr_to_kernel(compat_ptr(msg.msg_name),
+			err = move_addr_to_kernel(compat_ptr(msg->msg_name),
 						  kmsg->msg_namelen,
 						  kmsg->msg_name);
 			if (err < 0)
@@ -76,12 +71,10 @@ int __get_compat_msghdr(struct msghdr *kmsg,
 		kmsg->msg_namelen = 0;
 	}
 
-	if (msg.msg_iovlen > UIO_MAXIOV)
+	if (msg->msg_iovlen > UIO_MAXIOV)
 		return -EMSGSIZE;
 
 	kmsg->msg_iocb = NULL;
-	*ptr = msg.msg_iov;
-	*len = msg.msg_iovlen;
 	return 0;
 }
 
@@ -90,15 +83,17 @@ int get_compat_msghdr(struct msghdr *kmsg,
 		      struct sockaddr __user **save_addr,
 		      struct iovec **iov)
 {
-	compat_uptr_t ptr;
-	compat_size_t len;
+	struct compat_msghdr msg;
 	ssize_t err;
 
-	err = __get_compat_msghdr(kmsg, umsg, save_addr, &ptr, &len);
+	if (copy_from_user(&msg, umsg, sizeof(*umsg)))
+		return -EFAULT;
+
+	err = __get_compat_msghdr(kmsg, umsg, save_addr);
 	if (err)
 		return err;
 
-	err = import_iovec(save_addr ? READ : WRITE, compat_ptr(ptr), len,
+	err = import_iovec(save_addr ? READ : WRITE, compat_ptr(msg.msg_iov), msg.msg_iovlen,
 			   UIO_FASTIOV, iov, &kmsg->msg_iter);
 	return err < 0 ? err : 0;
 }
-- 
2.30.2