io_uring: Enable KASAN for request cache

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>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 8 insertions, 3 deletions

diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index d58cfe062da9..9270156288aa 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -4,6 +4,7 @@
 #include <linux/errno.h>
 #include <linux/lockdep.h>
 #include <linux/resume_user_mode.h>
+#include <linux/kasan.h>
 #include <linux/io_uring_types.h>
 #include <uapi/linux/eventpoll.h>
 #include "io-wq.h"
@@ -347,12 +348,16 @@ 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_defer_tw_run(struct io_ring_ctx *ctx)