lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date:   Fri, 2 Sep 2022 19:53:24 -0700
From:   Jakub Kicinski <>
To:     Kees Cook <>
Cc:     Pablo Neira Ayuso <>,
        Jozsef Kadlecsik <>,
        Florian Westphal <>,
        "David S. Miller" <>,
        Eric Dumazet <>,
        Paolo Abeni <>,
        syzbot <>,,,,
        Harshit Mogalapalli <>,,
Subject: Re: [PATCH v3] netlink: Bounds-check struct nlmsgerr creation

On Fri, 2 Sep 2022 16:08:01 -0700 Kees Cook wrote:
> > -	if (extack->cookie_len)
> > -		tlvlen += nla_total_size(extack->cookie_len);
> > +	if (extack->_msg &&
> > +	    check_add_overflow(*tlvlen, nla_total_size(strlen(extack->_msg) + 1), tlvlen))
> > +		return false;  
> If that's not desirable, then I guess the question I want to ask is
> "what can I put in the unsafe_memcpy() comment above that proves these
> values have been sanity checked? In other words, how do we know that
> tlvlen hasn't overflowed? (I don't know what other sanity checking may
> have already happened, so I'm looking directly at the size calculations
> here.)

The netlink helpers for adding attributes check whether there is enough
space left in the skb. So if the calculation overflows, so be it. We'll
hit EMSGSIZE in the writing phase and unwind. The writing should make
no assumptions about the skb size. In fact all dumps will routinely hit
EMSGSIZE as we try to fit as many objects into a skb as possible, so we
unwind the one that would go over. Unwinding is well exercised in a lot
of netlink code (not here, MSG_DONE/MSG_ERROR ain't a dump).

The pre-calculation is just an estimate, if the message size ends up
being insane it really doesn't matter if the calculation is 0, INT_MAX
or random(). User is not gonna get a response, anyway.

... unless someone uses the unsafe helpers like __nlmsg_put() rather
than nlmsg_put(), hence my suggestion in the other email.

Powered by blists - more mailing lists