[PATCH] w1: Split memcpy() of struct cn_msg flexible array

[PATCH] w1: Split memcpy() of struct cn_msg flexible array

[Kees Cook]

To work around a misbehavior of the compiler's ability to see into
composite flexible array structs (as detailed in the coming memcpy()
hardening series[1]), split the memcpy() of the header and the payload
so no false positive run-time overflow warning will be generated.

[1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org/

Cc: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/w1/w1_netlink.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/w1/w1_netlink.c b/drivers/w1/w1_netlink.c
index fa490aa4407c..db110cc442b1 100644
--- a/drivers/w1/w1_netlink.c
+++ b/drivers/w1/w1_netlink.c
@@ -611,7 +611,8 @@ static void w1_cn_callback(struct cn_msg *cn, struct netlink_skb_parms *nsp)
 		}
 		atomic_set(&block->refcnt, 1);
 		block->portid = nsp->portid;
-		memcpy(&block->request_cn, cn, sizeof(*cn) + cn->len);
+		block->request_cn = *cn;
+		memcpy(block->request_cn.data, cn->data, cn->len);
 		node = (struct w1_cb_node *)(block->request_cn.data + cn->len);
 
 		/* Sneeky, when not bundling, reply_size is the allocated space
-- 
2.34.1

Re: [PATCH] w1: Split memcpy() of struct cn_msg flexible array

[Gustavo A. R. Silva]

On Mon, Sep 26, 2022 at 05:39:27PM -0700, Kees Cook wrote:
> To work around a misbehavior of the compiler's ability to see into
> composite flexible array structs (as detailed in the coming memcpy()
> hardening series[1]), split the memcpy() of the header and the payload
> so no false positive run-time overflow warning will be generated.
> 
> [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org/
> 
> Cc: Evgeniy Polyakov <zbr@ioremap.net>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
--
Gustavo

> ---
>  drivers/w1/w1_netlink.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/w1/w1_netlink.c b/drivers/w1/w1_netlink.c
> index fa490aa4407c..db110cc442b1 100644
> --- a/drivers/w1/w1_netlink.c
> +++ b/drivers/w1/w1_netlink.c
> @@ -611,7 +611,8 @@ static void w1_cn_callback(struct cn_msg *cn, struct netlink_skb_parms *nsp)
>  		}
>  		atomic_set(&block->refcnt, 1);
>  		block->portid = nsp->portid;
> -		memcpy(&block->request_cn, cn, sizeof(*cn) + cn->len);
> +		block->request_cn = *cn;
> +		memcpy(block->request_cn.data, cn->data, cn->len);
>  		node = (struct w1_cb_node *)(block->request_cn.data + cn->len);
>  
>  		/* Sneeky, when not bundling, reply_size is the allocated space
> -- 
> 2.34.1
>