[PATCH 5.10 059/104] netfilter: nftables: fix possible UAF over chains from packet path in netns

Greg Kroah-Hartman
2021-02-15T15:40:39Z

From: Pablo Neira Ayuso <pablo@netfilter.org>

[ Upstream commit 767d1216bff82507c945e92fe719dff2083bb2f4 ]

Although hooks are released via call_rcu(), chain and rule objects are
immediately released while packets are still walking over these bits.

This patch adds the .pre_exit callback which is invoked before
synchronize_rcu() in the netns framework to stay safe.

Remove a comment which is not valid anymore since the core does not use
synchronize_net() anymore since 8c873e219970 ("netfilter: core: free
hooks with call_rcu").

Suggested-by: Florian Westphal <fw@strlen.de>
Fixes: df05ef874b28 ("netfilter: nf_tables: release objects on netns destruction")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nf_tables_api.c | 25 +++++++++++++++++++------
1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 9a080767667b7..8739ef135156b 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -8775,6 +8775,17 @@ int __nft_release_basechain(struct nft_ctx *ctx)
}
EXPORT_SYMBOL_GPL(__nft_release_basechain);

+static void __nft_release_hooks(struct net *net)
+{
+ struct nft_table *table;
+ struct nft_chain *chain;
+
+ list_for_each_entry(table, &net->nft.tables, list) {
+ list_for_each_entry(chain, &table->chains, list)
+ nf_tables_unregister_hook(net, table, chain);
+ }
+}
+
static void __nft_release_tables(struct net *net)
{
struct nft_flowtable *flowtable, *nf;
@@ -8790,10 +8801,6 @@ static void __nft_release_tables(struct net *net)

list_for_each_entry_safe(table, nt, &net->nft.tables, list) {
ctx.family = table->family;
-
- list_for_each_entry(chain, &table->chains, list)
- nf_tables_unregister_hook(net, table, chain);
- /* No packets are walking on these chains anymore. */
ctx.table = table;
list_for_each_entry(chain, &table->chains, list) {
ctx.chain = chain;
@@ -8842,6 +8849,11 @@ static int __net_init nf_tables_init_net(struct net *net)
return 0;
}

+static void __net_exit nf_tables_pre_exit_net(struct net *net)
+{
+ __nft_release_hooks(net);
+}
+
static void __net_exit nf_tables_exit_net(struct net *net)
{
mutex_lock(&net->nft.commit_mutex);
@@ -8855,8 +8867,9 @@ static void __net_exit nf_tables_exit_net(struct net *net)
}

static struct pernet_operations nf_tables_net_ops = {
- .init = nf_tables_init_net,
- .exit = nf_tables_exit_net,
+ .init = nf_tables_init_net,
+ .pre_exit = nf_tables_pre_exit_net,
+ .exit = nf_tables_exit_net,
};

static int __init nf_tables_module_init(void)
--
2.27.0