io_uring/cmd: don't expose entire cmd async data

io_uring needs private bits in cmd's ->async_data, and they should never
be exposed to drivers as it'd certainly be abused. Leave struct
io_uring_cmd_data for the drivers but wrap it into a structure. It's a
prep patch and doesn't do anything useful yet.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/20250319061251.21452-3-sidong.yang@furiosa.ai
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/io_uring.c

@@ -335,7 +335,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 			    sizeof(struct io_async_rw),
 			    offsetof(struct io_async_rw, clear));
 	ret |= io_alloc_cache_init(&ctx->cmd_cache, IO_ALLOC_CACHE_MAX,
-			    sizeof(struct io_uring_cmd_data), 0);
+			    sizeof(struct io_async_cmd), 0);
 	spin_lock_init(&ctx->msg_lock);
 	ret |= io_alloc_cache_init(&ctx->msg_cache, IO_ALLOC_CACHE_MAX,
 			    sizeof(struct io_kiocb), 0);

io_uring/opdef.c

@@ -416,7 +416,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.plug			= 1,
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
-		.async_size		= sizeof(struct io_uring_cmd_data),
+		.async_size		= sizeof(struct io_async_cmd),
 		.prep			= io_uring_cmd_prep,
 		.issue			= io_uring_cmd,
 	},

io_uring/uring_cmd.c

@@ -19,7 +19,8 @@
 static void io_req_uring_cleanup(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
-	struct io_uring_cmd_data *cache = req->async_data;
+	struct io_async_cmd *ac = req->async_data;
+	struct io_uring_cmd_data *cache = &ac->data;
 
 	if (cache->op_data) {
 		kfree(cache->op_data);
@@ -169,12 +170,15 @@ static int io_uring_cmd_prep_setup(struct io_kiocb *req,
 				   const struct io_uring_sqe *sqe)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
-	struct io_uring_cmd_data *cache;
+	struct io_async_cmd *ac;
 
-	cache = io_uring_alloc_async_data(&req->ctx->cmd_cache, req);
-	if (!cache)
+	/* see io_uring_cmd_get_async_data() */
+	BUILD_BUG_ON(offsetof(struct io_async_cmd, data) != 0);
+
+	ac = io_uring_alloc_async_data(&req->ctx->cmd_cache, req);
+	if (!ac)
 		return -ENOMEM;
-	cache->op_data = NULL;
+	ac->data.op_data = NULL;
 
 	/*
 	 * Unconditionally cache the SQE for now - this is only needed for
@@ -183,8 +187,8 @@ static int io_uring_cmd_prep_setup(struct io_kiocb *req,
 	 * that it doesn't read in per-op data, play it safe and ensure that
 	 * any SQE data is stable beyond prep. This can later get relaxed.
 	 */
-	memcpy(cache->sqes, sqe, uring_sqe_size(req->ctx));
-	ioucmd->sqe = cache->sqes;
+	memcpy(ac->data.sqes, sqe, uring_sqe_size(req->ctx));
+	ioucmd->sqe = ac->data.sqes;
 	return 0;
 }
 

io_uring/uring_cmd.h

@@ -1,5 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#include <linux/io_uring/cmd.h>
+
+struct io_async_cmd {
+	struct io_uring_cmd_data	data;
+};
+
 int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags);
 int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);