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netfilter: nf_tables: fix oops during rule dump 

We can oops in nf_tables_fill_rule_info().

Its not possible to fetch previous element in rcu-protected lists
when deletions are not prevented somehow: list_del_rcu poisons
the ->prev pointer value.

Before rcu-conversion this was safe as dump operations did hold
nfnetlink mutex.

Pass previous rule as argument, obtained by keeping a pointer to
the previous rule during traversal.

Fixes: d9adf22a29 ("netfilter: nf_tables: use call_rcu in netlink dumps")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2019-04-30 14:53:11 +02:00 committed by Pablo Neira Ayuso
parent ee8a2b95b7
commit 2c82c7e724
1 changed files with 11 additions and 9 deletions
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20
net/netfilter/nf_tables_api.c
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@ -2270,13 +2270,13 @@ static int nf_tables_fill_rule_info(struct sk_buff *skb, struct net *net,
u32 flags, int family,
const struct nft_table *table,
const struct nft_chain *chain,
const struct nft_rule *rule)
const struct nft_rule *rule,
const struct nft_rule *prule)
{
struct nlmsghdr *nlh;
struct nfgenmsg *nfmsg;
const struct nft_expr *expr, *next;
struct nlattr *list;
const struct nft_rule *prule;
u16 type = nfnl_msg_type(NFNL_SUBSYS_NFTABLES, event);
nlh = nlmsg_put(skb, portid, seq, type, sizeof(struct nfgenmsg), flags);
@ -2296,8 +2296,7 @@ static int nf_tables_fill_rule_info(struct sk_buff *skb, struct net *net,
NFTA_RULE_PAD))
goto nla_put_failure;
if ((event != NFT_MSG_DELRULE) && (rule->list.prev != &chain->rules)) {
prule = list_prev_entry(rule, list);
if (event != NFT_MSG_DELRULE && prule) {
if (nla_put_be64(skb, NFTA_RULE_POSITION,
cpu_to_be64(prule->handle),
NFTA_RULE_PAD))
@ -2344,7 +2343,7 @@ static void nf_tables_rule_notify(const struct nft_ctx *ctx,
err = nf_tables_fill_rule_info(skb, ctx->net, ctx->portid, ctx->seq,
event, 0, ctx->family, ctx->table,
ctx->chain, rule);
ctx->chain, rule, NULL);
if (err < 0) {
kfree_skb(skb);
goto err;
@ -2369,12 +2368,13 @@ static int __nf_tables_dump_rules(struct sk_buff *skb,
const struct nft_chain *chain)
{
struct net *net = sock_net(skb->sk);
const struct nft_rule *rule, *prule;
unsigned int s_idx = cb->args[0];
const struct nft_rule *rule;
prule = NULL;
list_for_each_entry_rcu(rule, &chain->rules, list) {
if (!nft_is_active(net, rule))
goto cont;
goto cont_skip;
if (*idx < s_idx)
goto cont;
if (*idx > s_idx) {
@ -2386,11 +2386,13 @@ static int __nf_tables_dump_rules(struct sk_buff *skb,
NFT_MSG_NEWRULE,
NLM_F_MULTI | NLM_F_APPEND,
table->family,
table, chain, rule) < 0)
table, chain, rule, prule) < 0)
return 1;
nl_dump_check_consistent(cb, nlmsg_hdr(skb));
cont:
prule = rule;
cont_skip:
(*idx)++;
}
return 0;
@ -2546,7 +2548,7 @@ static int nf_tables_getrule(struct net *net, struct sock *nlsk,
err = nf_tables_fill_rule_info(skb2, net, NETLINK_CB(skb).portid,
nlh->nlmsg_seq, NFT_MSG_NEWRULE, 0,
family, table, chain, rule);
family, table, chain, rule, NULL);
if (err < 0)
goto err;