io_uring: protect fixed file indexing with array_index_nospec()

We index the file tables with a user given value. After we check
it's within our limits, use array_index_nospec() to prevent any
spectre attacks here.

Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index b668149c20b9a5dcd30a0ee4024e726d0c17d146..7743b180a3e0a0a206a39840d3d5e2ea726a500a 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2321,6 +2321,7 @@ static int io_req_set_file(struct io_ring_ctx *ctx, const struct sqe_submit *s,
                if (unlikely(!ctx->user_files ||
                    (unsigned) fd >= ctx->nr_user_files))
                        return -EBADF;
+               fd = array_index_nospec(fd, ctx->nr_user_files);
                if (!ctx->user_files[fd])
                        return -EBADF;
                req->file = ctx->user_files[fd];