linux-kernel - Re: [PATCH] ksmbd: add kcov remote coverage support via ksmbd

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Message-ID: <d12e1d6a-d9e8-4bb3-abe4-9bcef1cb8f77@samba.org>
Date: Wed, 6 Aug 2025 14:14:50 +0200
From: Stefan Metzmacher <metze@...ba.org>
To: Yunseong Kim <ysk@...lloc.com>, Namjae Jeon <linkinjeon@...nel.org>,
 Steve French <smfrench@...il.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, Tom Talpey
 <tom@...pey.com>, linux-cifs@...r.kernel.org, syzkaller@...glegroups.com,
 linux-kernel@...r.kernel.org, notselwyn@...ing.tech
Subject: Re: [PATCH] ksmbd: add kcov remote coverage support via ksmbd_conn

Hi Yunseong,

Am 05.08.25 um 17:56 schrieb Yunseong Kim:
> KSMBD processes SMB requests on per-connection threads and then hands
> off work items to a kworker pool for actual command processing by
> handle_ksmbd_work(). Because each connection may enqueue multiple
> struct ksmbd_work instances, attaching the kcov handle to the work
> itself is not sufficient: we need a stable, per-connection handle.
> 
> Introduce a kcov_handle field on struct ksmbd_conn (under CONFIG_KCOV)
> and initialize it when the connection is set up. In both
> ksmbd_conn_handler_loop() which only receives a struct ksmbd_conn*
> and handle_ksmbd_work() which receives a struct ksmbd_work*, start
> kcov_remote with the per-connection handle before processing and stop
> it afterward. This ensures coverage collection remains active across
> the entire asynchronous path of each SMB request.
> 
> The kcov context tied to the connection itself, correctly supporting
> multiple outstanding work items per connection.
> 
> The related work for syzkaller support is currently being developed
> in the following GitHub PR:
> Link: https://github.com/google/syzkaller/pull/5524
> 
> Based on earlier work by Lau.
> Link: https://pwning.tech/ksmbd-syzkaller/
> 
> Cc: linux-cifs@...r.kernel.org
> Cc: notselwyn@...ing.tech
> Signed-off-by: Yunseong Kim <ysk@...lloc.com>
> ---
>   fs/smb/server/connection.c |  4 +++-
>   fs/smb/server/connection.h | 14 ++++++++++++++
>   fs/smb/server/server.c     |  4 ++++
>   3 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/smb/server/connection.c b/fs/smb/server/connection.c
> index 3f04a2977ba8..6ce20aee8cc1 100644
> --- a/fs/smb/server/connection.c
> +++ b/fs/smb/server/connection.c
> @@ -322,6 +322,8 @@ int ksmbd_conn_handler_loop(void *p)
>   	if (t->ops->prepare && t->ops->prepare(t))
>   		goto out;
>   
> +	kcov_remote_start_common(ksmbd_conn_get_kcov_handle(conn));
> +
>   	max_req = server_conf.max_inflight_req;
>   	conn->last_active = jiffies;
>   	set_freezable();
> @@ -412,7 +414,7 @@ int ksmbd_conn_handler_loop(void *p)
>   			break;
>   		}
>   	}
> -
> +	kcov_remote_stop();
>   out:
>   	ksmbd_conn_set_releasing(conn);
>   	/* Wait till all reference dropped to the Server object*/
> diff --git a/fs/smb/server/connection.h b/fs/smb/server/connection.h
> index dd3e0e3f7bf0..07cd0d27ac77 100644
> --- a/fs/smb/server/connection.h
> +++ b/fs/smb/server/connection.h
> @@ -15,6 +15,7 @@
>   #include <linux/kthread.h>
>   #include <linux/nls.h>
>   #include <linux/unicode.h>
> +#include <linux/kcov.h>
>   
>   #include "smb_common.h"
>   #include "ksmbd_work.h"
> @@ -109,6 +110,9 @@ struct ksmbd_conn {
>   	bool				binding;
>   	atomic_t			refcnt;
>   	bool				is_aapl;
> +#ifdef CONFIG_KCOV
> +	u64				kcov_handle;
> +#endif
>   };
>   
>   struct ksmbd_conn_ops {
> @@ -246,4 +250,14 @@ static inline void ksmbd_conn_set_releasing(struct ksmbd_conn *conn)
>   }
>   
>   void ksmbd_all_conn_set_status(u64 sess_id, u32 status);
> +
> +static inline u64 ksmbd_conn_get_kcov_handle(struct ksmbd_conn *conn)
> +{
> +#ifdef CONFIG_KCOV
> +	return conn->kcov_handle;
> +#else
> +	return 0;
> +#endif
> +}


conn->kcov_handle is a new element in ksmbd_conn
and I can't find the place in this patch where it is initialized...

metze