Re: [PATCH] io_uring: Enable KASAN for request cache

[Pavel Begunkov]

On 1/18/23 15:56, Breno Leitao wrote:
> 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.

Doesn't apply cleanly to for-6.3/io_uring, but otherwise looks good

Reviewed-by: Pavel Begunkov <asml.silence@xxxxxxxxx>

 
> Suggested-by: Jens Axboe <axboe@xxxxxxxxx>
> Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
> ---
>   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)

--
Pavel Begunkov