[PATCH nf v2] netfilter: conntrack: Avoid nf_ct_helper_hash uses after free

From: Florent Revest <revest@chromium.org>
To: netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	bpf@vger.kernel.org
Cc: pablo@netfilter.org, kadlec@netfilter.org, fw@strlen.de,
	davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
	pabeni@redhat.com, kpsingh@kernel.org, stable@vger.kernel.org,
	Florent Revest <revest@chromium.org>
Subject: [PATCH nf v2] netfilter: conntrack: Avoid nf_ct_helper_hash uses after free
Date: Mon,  3 Jul 2023 16:52:16 +0200	[thread overview]
Message-ID: <20230703145216.1096265-1-revest@chromium.org> (raw)

If nf_conntrack_init_start() fails (for example due to a
register_nf_conntrack_bpf() failure), the nf_conntrack_helper_fini()
clean-up path frees the nf_ct_helper_hash map.

When built with NF_CONNTRACK=y, further netfilter modules (e.g:
netfilter_conntrack_ftp) can still be loaded and call
nf_conntrack_helpers_register(), independently of whether nf_conntrack
initialized correctly. This accesses the nf_ct_helper_hash dangling
pointer and causes a uaf, possibly leading to random memory corruption.

This patch guards nf_conntrack_helper_register() from accessing a freed
or uninitialized nf_ct_helper_hash pointer and fixes possible
uses-after-free when loading a conntrack module.

Cc: stable@vger.kernel.org
Fixes: 12f7a505331e ("netfilter: add user-space connection tracking helper infrastructure")
Signed-off-by: Florent Revest <revest@chromium.org>
---
 net/netfilter/nf_conntrack_helper.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
index 0c4db2f2ac43..f22691f83853 100644
--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -360,6 +360,9 @@ int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 
+	if (!nf_ct_helper_hash)
+		return -ENOENT;
+
 	if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 		return -EINVAL;
 
@@ -515,4 +518,5 @@ int nf_conntrack_helper_init(void)
 void nf_conntrack_helper_fini(void)
 {
 	kvfree(nf_ct_helper_hash);
+	nf_ct_helper_hash = NULL;
 }
-- 
2.41.0.255.g8b1d071c50-goog

