[PATCH 5.5 102/119] io_uring: NULL-deref for IOSQE_{ASYNC,DRAIN}

[Greg Kroah-Hartman]

From: Pavel Begunkov <asml.silence@xxxxxxxxx>

[ Upstream commit f1d96a8fcbbbb22d4fbc1d69eaaa678bbb0ff6e2 ]

Processing links, io_submit_sqe() prepares requests, drops sqes, and
passes them with sqe=NULL to io_queue_sqe(). There IOSQE_DRAIN and/or
IOSQE_ASYNC requests will go through the same prep, which doesn't expect
sqe=NULL and fail with NULL pointer deference.

Always do full prepare including io_alloc_async_ctx() for linked
requests, and then it can skip the second preparation.

Cc: stable@xxxxxxxxxxxxxxx # 5.5
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/io_uring.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 44ae2641b4b06..faa0198c99ffd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3098,6 +3098,9 @@ static int io_req_defer_prep(struct io_kiocb *req,
 {
 	ssize_t ret = 0;
 
+	if (!sqe)
+		return 0;
+
 	switch (req->opcode) {
 	case IORING_OP_NOP:
 		break;
@@ -3681,6 +3684,11 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 			req->flags |= REQ_F_HARDLINK;
 
 		INIT_LIST_HEAD(&req->link_list);
+
+		if (io_alloc_async_ctx(req)) {
+			ret = -EAGAIN;
+			goto err_req;
+		}
 		ret = io_req_defer_prep(req, sqe);
 		if (ret)
 			req->flags |= REQ_F_FAIL_LINK;
-- 
2.20.1