[PATCH 5/7] io_uring/net: derive iovec storage later

[Pavel Begunkov <asml.silence@gmail.com>]

Don't read free_iov until right before we need it to import the iovec.
The only place that uses it before that is provided buffer selection,
but it only serves as temporary storage and iovec content is not reused
afterwards, so use a local variable for that.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/net.c | 43 +++++++++++++++++++++----------------------
 1 file changed, 21 insertions(+), 22 deletions(-)

diff --git a/io_uring/net.c b/io_uring/net.c
index 14eeebfd8a5a..8a9ec4783a2b 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -203,14 +203,6 @@ static int io_compat_msg_copy_hdr(struct io_kiocb *req,
 	struct iovec *iov;
 	int ret, nr_segs;
 
-	if (iomsg->free_iov) {
-		nr_segs = iomsg->free_iov_nr;
-		iov = iomsg->free_iov;
-	} else {
-		iov = &iomsg->fast_iov;
-		nr_segs = 1;
-	}
-
 	if (copy_from_user(msg, sr->umsg_compat, sizeof(*msg)))
 		return -EFAULT;
 
@@ -221,8 +213,7 @@ static int io_compat_msg_copy_hdr(struct io_kiocb *req,
 	uiov = compat_ptr(msg->msg_iov);
 	if (req->flags & REQ_F_BUFFER_SELECT) {
 		if (msg->msg_iovlen == 0) {
-			sr->len = iov->iov_len = 0;
-			iov->iov_base = NULL;
+			sr->len = 0;
 		} else if (msg->msg_iovlen > 1) {
 			return -EINVAL;
 		} else {
@@ -238,6 +229,14 @@ static int io_compat_msg_copy_hdr(struct io_kiocb *req,
 		return 0;
 	}
 
+	if (iomsg->free_iov) {
+		nr_segs = iomsg->free_iov_nr;
+		iov = iomsg->free_iov;
+	} else {
+		iov = &iomsg->fast_iov;
+		nr_segs = 1;
+	}
+
 	ret = __import_iovec(ddir, (struct iovec __user *)uiov, msg->msg_iovlen,
 				nr_segs, &iov, &iomsg->msg.msg_iter, true);
 	if (unlikely(ret < 0))
@@ -275,14 +274,6 @@ static int io_msg_copy_hdr(struct io_kiocb *req, struct io_async_msghdr *iomsg,
 	struct iovec *iov;
 	int ret, nr_segs;
 
-	if (iomsg->free_iov) {
-		nr_segs = iomsg->free_iov_nr;
-		iov = iomsg->free_iov;
-	} else {
-		iov = &iomsg->fast_iov;
-		nr_segs = 1;
-	}
-
 	ret = io_copy_msghdr_from_user(msg, umsg);
 	if (unlikely(ret))
 		return ret;
@@ -295,20 +286,28 @@ static int io_msg_copy_hdr(struct io_kiocb *req, struct io_async_msghdr *iomsg,
 
 	if (req->flags & REQ_F_BUFFER_SELECT) {
 		if (msg->msg_iovlen == 0) {
-			sr->len = iov->iov_len = 0;
-			iov->iov_base = NULL;
+			sr->len = 0;
 		} else if (msg->msg_iovlen > 1) {
 			return -EINVAL;
 		} else {
 			struct iovec __user *uiov = msg->msg_iov;
+			struct iovec tmp_iov;
 
-			if (copy_from_user(iov, uiov, sizeof(*iov)))
+			if (copy_from_user(&tmp_iov, uiov, sizeof(tmp_iov)))
 				return -EFAULT;
-			sr->len = iov->iov_len;
+			sr->len = tmp_iov.iov_len;
 		}
 		return 0;
 	}
 
+	if (iomsg->free_iov) {
+		nr_segs = iomsg->free_iov_nr;
+		iov = iomsg->free_iov;
+	} else {
+		iov = &iomsg->fast_iov;
+		nr_segs = 1;
+	}
+
 	ret = __import_iovec(ddir, msg->msg_iov, msg->msg_iovlen, nr_segs,
 				&iov, &iomsg->msg.msg_iter, false);
 	if (unlikely(ret < 0))
-- 
2.48.1