2023-07-03 15:25:32

by Florent Revest

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

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: [email protected]
Fixes: 12f7a505331e ("netfilter: add user-space connection tracking helper infrastructure")
Signed-off-by: Florent Revest <[email protected]>
---
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

2023-07-03 15:33:39

by Florian Westphal

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

Florent Revest <[email protected]> wrote:
> 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.

Reviewed-by: Florian Westphal <[email protected]>