linux-kernel - Re: [PATCH 0/3] Fix some seq_file users that were recently broken

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Date:   Sun, 7 Feb 2021 13:11:45 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     NeilBrown <neilb@...e.de>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>,
        Xin Long <lucien.xin@...il.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-sctp@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 0/3] Fix some seq_file users that were recently broken

On Sat, 6 Feb 2021 14:29:24 -0800 Jakub Kicinski <kuba@...nel.org> wrote:

> On Fri, 5 Feb 2021 14:35:50 -0800 Andrew Morton wrote:
> > On Fri, 05 Feb 2021 11:36:30 +1100 NeilBrown <neilb@...e.de> wrote:
> > 
> > > A recent change to seq_file broke some users which were using seq_file
> > > in a non-"standard" way ...  though the "standard" isn't documented, so
> > > they can be excused.  The result is a possible leak - of memory in one
> > > case, of references to a 'transport' in the other.
> > > 
> > > These three patches:
> > >  1/ document and explain the problem
> > >  2/ fix the problem user in x86
> > >  3/ fix the problem user in net/sctp
> > 
> > 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and
> > interface") was August 2018, so I don't think "recent" applies here?
> > 
> > I didn't look closely, but it appears that the sctp procfs file is
> > world-readable.  So we gave unprivileged userspace the ability to leak
> > kernel memory?
> > 
> > So I'm thinking that we aim for 5.12-rc1 on all three patches with a cc:stable?
> 
> I'd rather take the sctp patch sooner, we'll send another batch 
> of networking fixes for 5.11, anyway. Would that be okay with you?

Sure.