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

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Message-ID: <8736cfs73w.fsf@toke.dk>
Date:   Thu, 16 Jan 2020 17:23:31 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] netlink: make getters tolerate NULL nla arg

Florian Westphal <fw@...len.de> writes:

> 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.

I was thinking that at lack of NULL check could also imply a lack of
proper bounds checking. And that the crashes at least shine a light on
them forcing people to consider whether that is indeed the case?

(IDK if that's actually the case, I'm asking :))

-Toke