[PATCH 5.10 323/509] netfilter: conntrack: Avoid nf_ct_helper_hash uses after free

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From: Florent Revest <revest@xxxxxxxxxxxx>

commit 6eef7a2b933885a17679eb8ed0796ddf0ee5309b upstream.

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@xxxxxxxxxxxxxxx
Fixes: 12f7a505331e ("netfilter: add user-space connection tracking helper infrastructure")
Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx>
Reviewed-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/netfilter/nf_conntrack_helper.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -404,6 +404,9 @@ int nf_conntrack_helper_register(struct
 	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;
 
@@ -587,4 +590,5 @@ void nf_conntrack_helper_fini(void)
 {
 	nf_ct_extend_unregister(&helper_extend);
 	kvfree(nf_ct_helper_hash);
+	nf_ct_helper_hash = NULL;
 }





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