linux-kernel - Re: [PATCH net-next 1/2 v3] uevent: add alloc_uevent

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Date:   Fri, 27 Apr 2018 11:39:44 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, avagin@...tuozzo.com,
        ktkhai@...tuozzo.com, serge@...lyn.com, gregkh@...uxfoundation.org
Subject: Re: [PATCH net-next 1/2 v3] uevent: add alloc_uevent_skb() helper

Christian Brauner <christian.brauner@...ntu.com> writes:

> This patch adds alloc_uevent_skb() in preparation for follow up patches.
>
> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
> ---
>  lib/kobject_uevent.c | 39 ++++++++++++++++++++++++++-------------
>  1 file changed, 26 insertions(+), 13 deletions(-)
>
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index 15ea216a67ce..c3cb110f663b 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
> @@ -296,6 +296,31 @@ static void cleanup_uevent_env(struct subprocess_info *info)
>  }
>  #endif
>  
> +static struct sk_buff *alloc_uevent_skb(struct kobj_uevent_env *env,
> +					const char *action_string,
> +					const char *devpath)
> +{
> +	struct sk_buff *skb = NULL;
> +	char *scratch;
> +	size_t len;
> +
> +	/* allocate message with maximum possible size */
> +	len = strlen(action_string) + strlen(devpath) + 2;
> +	skb = alloc_skb(len + env->buflen, GFP_KERNEL);
> +	if (!skb)
> +		return NULL;
> +
> +	/* add header */
> +	scratch = skb_put(skb, len);
> +	sprintf(scratch, "%s@%s", action_string, devpath);
> +
> +	skb_put_data(skb, env->buf, env->buflen);
> +
> +	NETLINK_CB(skb).dst_group = 1;

nit:
     We might want to explicitly set NETLINK_CB(skb).portid to 0 and
     NETLINK_CB(skb).creds.uid to GLOBAL_ROOT_UID and
     NETLINK_CB(skb).creds.gid to GLOBAL_ROOT_GID here
     just to make it clear this is happening.

     It is not a problem because they __alloc_skb memsets to 0 the
     fields of struct sk_buff that it does not initialize.  And these
     are the zero values.

     Still it would be nice to be able to look at the code and quickly
     see these are the values being set.

Eric