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 1b2517291b7870ebb49c3999d9a19c62b6f8bb25..b1fbc4424aa63c7c0dc5ca0c02d40f8f2637a0c8 100644 (file)
--- 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 @@ err_req:
                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;