re: netfilter: nft_ct: add ct expectations support

Hi,

Static analysis with Coverity on linux-next has found a potential issue
with the following commit:

commit 857b46027d6f91150797295752581b7155b9d0e1
Author: Stéphane Veyret [off-list ref]
Date:   Sat May 25 15:30:58 2019 +0200

    netfilter: nft_ct: add ct expectations support


Specifically in function nft_ct_expect_obj_eval)() in the following code:

+       help = nfct_help(ct);
+       if (!help)
+               help = nf_ct_helper_ext_add(ct, GFP_ATOMIC);
+
+       if (help->expecting[NF_CT_EXPECT_CLASS_DEFAULT] >= priv->size) {
+               regs->verdict.code = NFT_BREAK;
+               return;
+       }


The call to nf_ct_helper_ext_add can potentially return NULL, however,
this is not being checked and pointer 'help' is being dereferenced even
though it potentially can be null.

Colin