io_uring/rsrc: use nospec'ed indexes

We use array_index_nospec() for registered buffer indexes, but don't use
it while poking into rsrc tags, fix that.

Fixes: 634d00df ("io_uring: add full-fledged dynamic buffers support")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/f02fafc5a9c0dd69be2b0618c38831c078232ff0.1681395792.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/rsrc.c

@@ -517,7 +517,7 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 		}
 
 		ctx->user_bufs[i] = imu;
-		*io_get_tag_slot(ctx->buf_data, offset) = tag;
+		*io_get_tag_slot(ctx->buf_data, i) = tag;
 	}
 
 	if (needs_switch)