[PATCH] io_uring: fix off-by-one in sync cancelation file check

[Jens Axboe <axboe@kernel.dk>]

The passed in index should be validated against the number of registered
files we have, it needs to be smaller than the index value to avoid going
one beyond the end.

Fixes: 78a861b94959 ("io_uring: add sync cancelation API through io_uring_register()")
Reported-by: Luo Likang <luolikang@nsfocus.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/io_uring/cancel.c b/io_uring/cancel.c
index e4e1dc0325f0..5fc5d3e80fcb 100644
--- a/io_uring/cancel.c
+++ b/io_uring/cancel.c
@@ -218,7 +218,7 @@ static int __io_sync_cancel(struct io_uring_task *tctx,
 	    (cd->flags & IORING_ASYNC_CANCEL_FD_FIXED)) {
 		unsigned long file_ptr;
 
-		if (unlikely(fd > ctx->nr_user_files))
+		if (unlikely(fd >= ctx->nr_user_files))
 			return -EBADF;
 		fd = array_index_nospec(fd, ctx->nr_user_files);
 		file_ptr = io_fixed_file_slot(&ctx->file_table, fd)->file_ptr;

-- 
Jens Axboe