The patch below does not apply to the 5.5-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f1d96a8fcbbbb22d4fbc1d69eaaa678bbb0ff6e2 Mon Sep 17 00:00:00 2001

From: Pavel Begunkov asml.silence@gmail.com Date: Fri, 13 Mar 2020 22:29:14 +0300 Subject: [PATCH] io_uring: NULL-deref for IOSQE_{ASYNC,DRAIN}

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@vger.kernel.org # 5.5 Signed-off-by: Pavel Begunkov asml.silence@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/fs/io_uring.c b/fs/io_uring.c index 1b2517291b78..b1fbc4424aa6 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -4131,6 +4131,9 @@ static int io_req_defer_prep(struct io_kiocb *req, { ssize_t ret = 0;

+ if (!sqe) + return 0; + if (io_op_defs[req->opcode].file_table) { ret = io_grab_files(req); if (unlikely(ret)) @@ -4907,6 +4910,11 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe, if (sqe_flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK)) { req->flags |= REQ_F_LINK; 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;