Subject: [REGRESSION] netfilter: conntrack: Unable to change conntrack accounting of a net namespace via 'nf_conntrack_acct' sysfs

From: Shmulik Ladkani <[email-masked]>
Date: Tue, 27 Aug 2019 13:57:54 +0300

Hi,

Prior d912dec12428 ("netfilter: conntrack: merge acct and helper sysctl table with main one")
one was able to enable extended accounting within a (non-init)
net-namespace by setting: 'net.netfilter.nf_conntrack_acct=1'

However since d912dec12428, doing so results in changing init_net's
sysctl_acct field, instead of the relevant net's sysctl_acct.

Seen in original code, PRE d912dec12428, which creates a reference to
each net's _OWN_ ct.sysctl_acct within a separate acct_sysctl_table,
snip:

-static int nf_conntrack_acct_init_sysctl(struct net *net)
-{
-	struct ctl_table *table;
-
-	table = kmemdup(acct_sysctl_table, sizeof(acct_sysctl_table),
-			GFP_KERNEL);
-	if (!table)
-		goto out;
-
-	table[0].data = &net->ct.sysctl_acct;
-

(where 'nf_conntrack_acct_init_sysctl()' was originally called by
'nf_conntrack_acct_pernet_init()').

However POST d912dec12428, the per-net netfilter sysctl table simply
inherits from global 'nf_ct_sysctl_table[]', which has 

+		.data		= &init_net.ct.sysctl_acct,

effectivly making any 'net.netfilter.nf_conntrack_acct' sysctl change
affect the 'init_net' and not relevant net namespace.

Also, looks like "nf_conntrack_helper", "nf_conntrack_events",
"nf_conntrack_timestamp" where also harmed in a similar way, see:

  d912dec12428 ("netfilter: conntrack: merge acct and helper sysctl table with main one")
  cb2833ed0044 ("netfilter: conntrack: merge ecache and timestamp sysctl tables with main one")

Florian, would it be possible for you to revert these on -net ?

Many thanks,
Shmulik