netdev - Re: [PATCH net-next] netlink: make getters tolerate NULL nla arg

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Message-ID: <20200116160435.GT795@breakpoint.cc>
Date:   Thu, 16 Jan 2020 17:04:35 +0100
From:   Florian Westphal <fw@...len.de>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] netlink: make getters tolerate NULL nla arg

Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> Florian Westphal <fw@...len.de> writes:
> 
> > One recurring bug pattern triggered by syzbot is NULL dereference in
> > netlink code paths due to a missing "tb[NL_ARG_FOO] != NULL" test.
> >
> > At least some of these missing checks would not have crashed the kernel if
> > the various nla_get_XXX helpers would return 0 in case of missing arg.
> 
> Won't this risk just papering over the issue and lead to subtly wrong
> behaviour instead? At least a crash is somewhat visible :)

How?  Its no different than tb[X] being set with a 0 value.