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

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Date:   Sat, 28 Apr 2018 21:09:45 +0200
From:   Christian Brauner <christian.brauner@...onical.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.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

On Fri, Apr 27, 2018 at 11:39:44AM -0500, Eric W. Biederman wrote:
> 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.

Don't really mind adding it. Ok, non-functional changes added to the new
version. But then let's set "portid" too:

	parms = &NETLINK_CB(skb);
	parms->creds.uid = GLOBAL_ROOT_UID;
	parms->creds.gid = GLOBAL_ROOT_GID;
	parms->dst_group = 1;
	parms->portid = 0;

Christian