netdev - Re: [PATCH iptables] libxt_cgroup2: add support for cgroup2 path matching

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Date:	Wed, 18 Nov 2015 00:02:01 +0100 (CET)
From:	Jan Engelhardt <jengelh@...i.de>
To:	Tejun Heo <tj@...nel.org>
cc:	davem@...emloft.net, pablo@...filter.org, kaber@...sh.net,
	kadlec@...ckhole.kfki.hu, lizefan@...wei.com, hannes@...xchg.org,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-team@...com,
	daniel@...earbox.net, daniel.wagner@...-carit.de,
	nhorman@...driver.com
Subject: Re: [PATCH iptables] libxt_cgroup2: add support for cgroup2 path
 matching


On Tuesday 2015-11-17 20:42, Tejun Heo wrote:
>+static void cgroup2_save(const void *ip, const struct xt_entry_match *match)
>+{
>+	const struct xt_cgroup2_info *info = (void *)match->data;
>+
>+	printf("%s --path %s", info->invert ? " !" : "", info->path);
>+}

Can cgroup path names contain anything fancy, like spaces, backslashes, etc.?
If so, xtables_save_string() will be needed here.

>+static struct xtables_match cgroup2_match = {
>+	.family		= NFPROTO_UNSPEC,
>+	.name		= "cgroup2",
>+	.version	= XTABLES_VERSION,
>+	.size		= XT_ALIGN(sizeof(struct xt_cgroup2_info)),
>+	.userspacesize	= XT_ALIGN(sizeof(struct xt_cgroup2_info)),

userspacesize must not include xt_cgroup2_info.priv.
Change to offsetof(...), cf. other .c modules which do this.


>+++ b/extensions/libxt_cgroup2.man
>@@ -0,0 +1,24 @@
>+.TP
>+[\fB!\fP] \fB\-\-path\fP \fIpath\fP
>+Match cgroup2 membership.
>+
>+Each socket is associated with the v2 cgroup of the creating process.
>+This matches packets coming from or going to all sockets in the
>+sub-hierarchy of the specified path.  The path should be relative to
>+the root of the cgroup2 hierarchy.  Can be used in the OUTPUT and
>+INPUT chains to assign particular firewall policies for aggregated
>+processes on the system. This allows for more fine-grained firewall
>+policies that only match for a subset of the system's processes.
>+
>+\fBIMPORTANT\fP: when being used in the INPUT chain, the cgroup2
>+matcher is currently only of limited functionality, meaning it
>+will only match on packets that are processed for local sockets
>+through early socket demuxing. Therefore, general usage on the
>+INPUT chain is disadviced unless the implications are well

is disadviced (sic)  -> is not advised
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