On Thu, Jun 15, 2023 at 05:29:18PM +0200, Florent Revest wrote:
> If register_nf_conntrack_bpf() fails (for example, if the .BTF section
> contains an invalid entry), nf_conntrack_init_start() calls
> nf_conntrack_helper_fini() as part of its cleanup path and
> nf_ct_helper_hash gets freed.
>
> Further netfilter modules like netfilter_conntrack_ftp don't check
> whether nf_conntrack initialized correctly and call
> nf_conntrack_helpers_register() which accesses the freed
> nf_ct_helper_hash and causes a uaf.
>
> This patch guards nf_conntrack_helper_register() from accessing
> freed/uninitialized nf_ct_helper_hash maps and fixes a boot-time
> use-after-free.
How could this possibly happen?
nf_conntrack_ftp depends on nf_conntrack.
If nf_conntrack fails to load, how can nf_conntrack_ftp be loaded?
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 12f7a505331e ("netfilter: add user-space connection tracking helper infrastructure")
> Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx>
> ---
> 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;
> }
> --
> 2.41.0.162.gfafddb0af9-goog
>
