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

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Message-ID: <20200119123239.GB795@breakpoint.cc>
Date:   Sun, 19 Jan 2020 13:32:39 +0100
From:   Florian Westphal <fw@...len.de>
To:     David Miller <davem@...emloft.net>
Cc:     fw@...len.de, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] netlink: make getters tolerate NULL nla arg

David Miller <davem@...emloft.net> wrote:
> From: Florian Westphal <fw@...len.de>
> Date: Thu, 16 Jan 2020 15:55:22 +0100
> 
> > 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.
> > 
> > Make the helpers return 0 instead of crashing when a null nla is provided.
> > Even with allyesconfig the .text increase is only about 350 bytes.
> > 
> > Signed-off-by: Florian Westphal <fw@...len.de>
> 
> Sorry, I think it's better to find out when code is trying to access
> attributes without verifying that they are even supplied.

Less than 24 hours after I saw this patch marked rejected syzbot
reported another incarnation of this pattern.

Would you consider a v2 with a WARN_ON_ONCE() added (and the
buildbot warning resolved)?

Thanks.