[PATCH] io_uring: Enable KASAN for request cache

[Breno Leitao <leitao@debian.org>]

Every io_uring request is represented by struct io_kiocb, which is
cached locally by io_uring (not SLAB/SLUB) in the list called
submit_state.freelist. This patch simply enabled KASAN for this free
list.

This list is initially created by KMEM_CACHE, but later, managed by
io_uring. This patch basically poisons the objects that are not used
(i.e., they are the free list), and unpoisons it when the object is
allocated/removed from the list.

Touching these poisoned objects while in the freelist will cause a KASAN
warning.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 io_uring/io_uring.c |  3 ++-
 io_uring/io_uring.h | 11 ++++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 2ac1cd8d23ea..8cc0f12034d1 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -151,7 +151,7 @@ static void io_move_task_work_from_local(struct io_ring_ctx *ctx);
 static void __io_submit_flush_completions(struct io_ring_ctx *ctx);
 static __cold void io_fallback_tw(struct io_uring_task *tctx);
 
-static struct kmem_cache *req_cachep;
+struct kmem_cache *req_cachep;
 
 struct sock *io_uring_get_socket(struct file *file)
 {
@@ -230,6 +230,7 @@ static inline void req_fail_link_node(struct io_kiocb *req, int res)
 static inline void io_req_add_to_cache(struct io_kiocb *req, struct io_ring_ctx *ctx)
 {
 	wq_stack_add_head(&req->comp_list, &ctx->submit_state.free_list);
+	kasan_poison_object_data(req_cachep, req);
 }
 
 static __cold void io_ring_ctx_ref_free(struct percpu_ref *ref)
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index ab4b2a1c3b7e..0ccf62a19b65 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -3,6 +3,7 @@
 
 #include <linux/errno.h>
 #include <linux/lockdep.h>
+#include <linux/kasan.h>
 #include <linux/io_uring_types.h>
 #include <uapi/linux/eventpoll.h>
 #include "io-wq.h"
@@ -379,12 +380,16 @@ static inline bool io_alloc_req_refill(struct io_ring_ctx *ctx)
 	return true;
 }
 
+extern struct kmem_cache *req_cachep;
+
 static inline struct io_kiocb *io_alloc_req(struct io_ring_ctx *ctx)
 {
-	struct io_wq_work_node *node;
+	struct io_kiocb *req;
 
-	node = wq_stack_extract(&ctx->submit_state.free_list);
-	return container_of(node, struct io_kiocb, comp_list);
+	req = container_of(ctx->submit_state.free_list.next, struct io_kiocb, comp_list);
+	kasan_unpoison_object_data(req_cachep, req);
+	wq_stack_extract(&ctx->submit_state.free_list);
+	return req;
 }
 
 static inline bool io_allowed_run_tw(struct io_ring_ctx *ctx)
-- 
2.30.2