linux-kernel - [PATCH 4/4] io_uring: don't read user-shared sqe flags twice

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Date:   Wed,  8 Apr 2020 08:58:46 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 4/4] io_uring: don't read user-shared sqe flags twice

Don't re-read userspace-shared sqe->flags, it can be exploited.
sqe->flags are copied into req->flags in io_submit_sqe(), check them
instead.

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 fs/io_uring.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 072e002f1184..f8173a77434c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2930,7 +2930,7 @@ static int io_openat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	if (sqe->ioprio || sqe->buf_index)
 		return -EINVAL;
-	if (sqe->flags & IOSQE_FIXED_FILE)
+	if (req->flags & REQ_F_FIXED_FILE)
 		return -EBADF;
 	if (req->flags & REQ_F_NEED_CLEANUP)
 		return 0;
@@ -2961,7 +2961,7 @@ static int io_openat2_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	if (sqe->ioprio || sqe->buf_index)
 		return -EINVAL;
-	if (sqe->flags & IOSQE_FIXED_FILE)
+	if (req->flags & REQ_F_FIXED_FILE)
 		return -EBADF;
 	if (req->flags & REQ_F_NEED_CLEANUP)
 		return 0;
@@ -3315,7 +3315,7 @@ static int io_statx_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	if (sqe->ioprio || sqe->buf_index)
 		return -EINVAL;
-	if (sqe->flags & IOSQE_FIXED_FILE)
+	if (req->flags & REQ_F_FIXED_FILE)
 		return -EBADF;
 	if (req->flags & REQ_F_NEED_CLEANUP)
 		return 0;
@@ -3392,7 +3392,7 @@ static int io_close_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (sqe->ioprio || sqe->off || sqe->addr || sqe->len ||
 	    sqe->rw_flags || sqe->buf_index)
 		return -EINVAL;
-	if (sqe->flags & IOSQE_FIXED_FILE)
+	if (req->flags & REQ_F_FIXED_FILE)
 		return -EBADF;
 
 	req->close.fd = READ_ONCE(sqe->fd);
@@ -5363,15 +5363,10 @@ static int io_file_get(struct io_submit_state *state, struct io_kiocb *req,
 }
 
 static int io_req_set_file(struct io_submit_state *state, struct io_kiocb *req,
-			   const struct io_uring_sqe *sqe)
+			   int fd, unsigned int flags)
 {
-	unsigned flags;
-	int fd;
 	bool fixed;
 
-	flags = READ_ONCE(sqe->flags);
-	fd = READ_ONCE(sqe->fd);
-
 	if (!io_req_needs_file(req, fd))
 		return 0;
 
@@ -5613,7 +5608,7 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 {
 	struct io_ring_ctx *ctx = req->ctx;
 	unsigned int sqe_flags;
-	int ret, id;
+	int ret, id, fd;
 
 	sqe_flags = READ_ONCE(sqe->flags);
 
@@ -5644,7 +5639,8 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 					IOSQE_ASYNC | IOSQE_FIXED_FILE |
 					IOSQE_BUFFER_SELECT);
 
-	ret = io_req_set_file(state, req, sqe);
+	fd = READ_ONCE(sqe->fd);
+	ret = io_req_set_file(state, req, fd, sqe_flags);
 	if (unlikely(ret)) {
 err_req:
 		io_cqring_add_event(req, ret);
-- 
2.24.0