io_uring: fix index calculation

When indexing into a provided buffer ring, do not subtract 1 from the
index.

Fixes: c7fb19428d67 ("io_uring: add support for ring mapped supplied buffers")
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220613101157.3687-2-dylany@fb.com
Reviewed-by: Hao Xu <howeyxu@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 3aab418..9cf9aff 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3888,7 +3888,7 @@ static void __user *io_ring_buffer_select(struct io_kiocb *req, size_t *len,
                buf = &br->bufs[head];
        } else {
                int off = head & (IO_BUFFER_LIST_BUF_PER_PAGE - 1);
-               int index = head / IO_BUFFER_LIST_BUF_PER_PAGE - 1;
+               int index = head / IO_BUFFER_LIST_BUF_PER_PAGE;
                buf = page_address(bl->buf_pages[index]);
                buf += off;
        }