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

[Florian Westphal]

Florent Revest <revest@xxxxxxxxxxxx> 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 <fw@xxxxxxxxx>