netdev - Re: [PATCH net] fib_rules: return 0 directly if an exactly same rule exists when NLM_F

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Message-ID: <CAHo-OozeC3o9avh5kgKpXq1koRH0fVtNRaM9mb=vduYRNX0T7g@mail.gmail.com>
Date:   Fri, 31 May 2019 18:43:42 -0700
From:   Maciej Żenczykowski <zenczykowski@...il.com>
To:     David Miller <davem@...emloft.net>,
        Lorenzo Colitti <lorenzo@...gle.com>, astrachan@...gle.com,
        Greg KH <greg@...ah.com>
Cc:     liuhangbin@...il.com, Linux NetDev <netdev@...r.kernel.org>,
        mateusz.bajorski@...ia.com, dsa@...ulusnetworks.com
Subject: Re: [PATCH net] fib_rules: return 0 directly if an exactly same rule
 exists when NLM_F_EXCL not supplied

FYI, this userspace visible change in behaviour breaks Android.

We rely on being able to add a rule and either have a dup be created
(in which case we'll remove it later) or have it fail with EEXIST (in
which case we won't remove it later).

Returning 0 makes atomically changing a rule difficult.

Please revert.

On Wed, May 8, 2019 at 9:39 AM David Miller <davem@...emloft.net> wrote:
>
> From: Hangbin Liu <liuhangbin@...il.com>
> Date: Tue,  7 May 2019 17:11:18 +0800
>
> > With commit 153380ec4b9 ("fib_rules: Added NLM_F_EXCL support to
> > fib_nl_newrule") we now able to check if a rule already exists. But this
> > only works with iproute2. For other tools like libnl, NetworkManager,
> > it still could add duplicate rules with only NLM_F_CREATE flag, like
> >
> > [localhost ~ ]# ip rule
> > 0:      from all lookup local
> > 32766:  from all lookup main
> > 32767:  from all lookup default
> > 100000: from 192.168.7.5 lookup 5
> > 100000: from 192.168.7.5 lookup 5
> >
> > As it doesn't make sense to create two duplicate rules, let's just return
> > 0 if the rule exists.
> >
> > Fixes: 153380ec4b9 ("fib_rules: Added NLM_F_EXCL support to fib_nl_newrule")
> > Reported-by: Thomas Haller <thaller@...hat.com>
> > Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
>
> Applied and queued up for -stable, thanks.