io_uring: fix double prep iovec leak

mainline inclusion
from mainline-5.6-rc2
commit 5f798bea
category: feature
bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=27
CVE: NA
---------------------------

Requests may be prepared multiple times with ->io allocated (i.e. async
prepared). Preparation functions don't handle it and forget about
previously allocated resources. This may happen in case of:
- spurious defer_check
- non-head (i.e. async prepared) request executed in sync (via nxt).

Make the handlers check, whether they already allocated resources, which
is true IFF REQ_F_NEED_CLEANUP is set.

Cc: stable@vger.kernel.org # 5.5
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: Nyangerkun <yangerkun@huawei.com>
Reviewed-by: Nzhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>

fs/io_uring.c

@@ -2199,7 +2199,8 @@ static int io_read_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (unlikely(!(req->file->f_mode & FMODE_READ)))
 		return -EBADF;
 
-	if (!req->io)
+	/* either don't need iovec imported or already have it */
+	if (!req->io || req->flags & REQ_F_NEED_CLEANUP)
 		return 0;
 
 	io = req->io;
@@ -2287,7 +2288,8 @@ static int io_write_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (unlikely(!(req->file->f_mode & FMODE_WRITE)))
 		return -EBADF;
 
-	if (!req->io)
+	/* either don't need iovec imported or already have it */
+	if (!req->io || req->flags & REQ_F_NEED_CLEANUP)
 		return 0;
 
 	io = req->io;
@@ -2941,6 +2943,9 @@ static int io_sendmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	if (!io || req->opcode == IORING_OP_SEND)
 		return 0;
+	/* iovec is already imported */
+	if (req->flags & REQ_F_NEED_CLEANUP)
+		return 0;
 
 	io->msg.iov = io->msg.fast_iov;
 	ret = sendmsg_copy_msghdr(&io->msg.msg, sr->msg, sr->msg_flags,
@@ -3091,6 +3096,9 @@ static int io_recvmsg_prep(struct io_kiocb *req,
 
 	if (!io || req->opcode == IORING_OP_RECV)
 		return 0;
+	/* iovec is already imported */
+	if (req->flags & REQ_F_NEED_CLEANUP)
+		return 0;
 
 	io->msg.iov = io->msg.fast_iov;
 	ret = recvmsg_copy_msghdr(&io->msg.msg, sr->msg, sr->msg_flags,