commit b7620121dc04e44ce654297050f9eaf39d414a34
author Jens Axboe <axboe@kernel.dk> Sat Oct 26 07:22:55 2019 -0600
committer Jens Axboe <axboe@kernel.dk> Tue Oct 29 12:43:06 2019 -0600
tree 6f6ea0f8c5c240d76678841d96c3df79244b2a5a
parent 17f2fe35d080d8f64e86a60cdcd3a97edcbc213b

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>

fs/io_uring.c

diff --git a/fs/io_uring.c b/fs/io_uring.c
index b668149..7743b18 100644
--- 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];