netdev - Re: [Patch net] net: make pskb_trim_rcsum

lists.openwall.net		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 linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAM_iQpW8DAJvP=xpTA0XeMnaHa=-cwkNwxmcfOSYWnCMZefGOw@mail.gmail.com>
Date:   Tue, 30 Oct 2018 11:57:13 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [Patch net] net: make pskb_trim_rcsum_slow() robust

On Mon, Oct 29, 2018 at 8:08 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
>
> On 10/29/2018 07:41 PM, Cong Wang wrote:
> > On Mon, Oct 29, 2018 at 7:25 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
> >>
> >>
> >>
> >> On 10/29/2018 07:21 PM, Cong Wang wrote:
> >>> On Mon, Oct 29, 2018 at 7:14 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
> >>>>
> >>>> Would not it be simpler to set ip_summed to CHECKSUM_NONE (no need to save old_csum) ?
> >>>
> >>> For !CHECKSUM_COMPLETE, ip_summed should be untouched, right?
> >>>
> >>> If you mean only setting to CHECKSUM_NONE for CHECKSUM_COMPLETE case,
> >>> the end result may not be simpler.
> >>
> >> I meant to reinstate what was there before my patch in this error case
> >>
> >>        if (skb->ip_summed == CHECKSUM_COMPLETE)
> >>                skb->ip_summed = CHECKSUM_NONE;
> >>
> >> That would only be run in error (quite unlikely) path, instead of saving old_csum in all cases.
> >
> > I know your point, however, I am not sure that is a desired behavior.
> >
> > On failure, I think the whole skb should be restored to its previous state
> > before entering this function, changing it to CHECKSUM_NONE on failure
> > is inconsistent with success case.
> >
>
> Before my patch, we were changing skb->ip_summed to CHECKSUM_NONE,
> so why suddenly we need to be consistent ?

That is because setting it to CHECKSUM_NONE _was_ how the success
case works and nothing _was_ needed for failure case.

You changed how we handle checksum for success case, it is why we need
to change for the failure case too.


>
> In any case, ip_check_defrag() should really drop this skb, as for other allocation
> failures (like skb_share_check()), if really we want consistency.

I have the same feeling, just not brave enough to change the logic of
ip_check_defrag() where pskb_may_pull() failure is treated in a same way.