netfilter: nft_ct: fix use after free when attaching zone template

The conversion erroneously removed the refcount increment.
In case we can use the percpu template, we need to increment
the refcount, else it will be released when the skb gets freed.

In case the slowpath is taken, the new template already has a
refcount of 1.

Fixes: 719774377622 ("netfilter: conntrack: convert to refcount_t api")
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nft_ct.c b/net/netfilter/nft_ct.c
index 518d96c8c247143729f5aa161e49e5574716b2cd..5adf8bb628a80eadc073a2a064910b15b2ae2b1c 100644 (file)
--- a/net/netfilter/nft_ct.c
+++ b/net/netfilter/nft_ct.c
@@ -260,9 +260,12 @@ static void nft_ct_set_zone_eval(const struct nft_expr *expr,
        ct = this_cpu_read(nft_ct_pcpu_template);
 
        if (likely(refcount_read(&ct->ct_general.use) == 1)) {
+               refcount_inc(&ct->ct_general.use);
                nf_ct_zone_add(ct, &zone);
        } else {
-               /* previous skb got queued to userspace */
+               /* previous skb got queued to userspace, allocate temporary
+                * one until percpu template can be reused.
+                */
                ct = nf_ct_tmpl_alloc(nft_net(pkt), &zone, GFP_ATOMIC);
                if (!ct) {
                        regs->verdict.code = NF_DROP;