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netfilter: nf_tables: support for recursive chain deletion

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This patch sorts out an asymmetry in deletions. Currently, table and set
deletion commands come with an implicit content flush on deletion.
However, chain deletion results in -EBUSY if there is content in this
chain, so no implicit flush happens. So you have to send a flush command
in first place to delete chains, this is inconsistent and it can be
annoying in terms of user experience.

This patch uses the new NLM_F_NONREC flag to request non-recursive chain
deletion, ie. if the chain to be removed contains rules, then this
returns EBUSY. This problem was discussed during the NFWS'17 in Faro,
Portugal. In iptables, you hit -EBUSY if you try to delete a chain that
contains rules, so you have to flush first before you can remove
anything. Since iptables-compat uses the nf_tables netlink interface, it
has to use the NLM_F_NONREC flag from userspace to retain the original
iptables semantics, ie.  bail out on removing chains that contain rules.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Pablo Neira Ayuso 2017-09-03 23:56:01 +02:00
parent a827840080
commit 9dee147412
1 changed files with 23 additions and 1 deletions
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24
net/netfilter/nf_tables_api.c
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@ -1617,8 +1617,11 @@ static int nf_tables_delchain(struct net *net, struct sock *nlsk,
struct nft_af_info *afi;
struct nft_table *table;
struct nft_chain *chain;
struct nft_rule *rule;
int family = nfmsg->nfgen_family;
struct nft_ctx ctx;
u32 use;
int err;
afi = nf_tables_afinfo_lookup(net, family, false);
if (IS_ERR(afi))
@ -1631,11 +1634,30 @@ static int nf_tables_delchain(struct net *net, struct sock *nlsk,
chain = nf_tables_chain_lookup(table, nla[NFTA_CHAIN_NAME], genmask);
if (IS_ERR(chain))
return PTR_ERR(chain);
if (chain->use > 0)
if (nlh->nlmsg_flags & NLM_F_NONREC &&
chain->use > 0)
return -EBUSY;
nft_ctx_init(&ctx, net, skb, nlh, afi, table, chain, nla);
use = chain->use;
list_for_each_entry(rule, &chain->rules, list) {
if (!nft_is_active_next(net, rule))
continue;
use--;
err = nft_delrule(&ctx, rule);
if (err < 0)
return err;
}
/* There are rules and elements that are still holding references to us,
* we cannot do a recursive removal in this case.
*/
if (use > 0)
return -EBUSY;
return nft_delchain(&ctx);
}