linux-kernel - Re: [PATCH -next] mm: delete oversized WARN

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Date:   Thu, 2 Dec 2021 07:34:36 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jeremy Sowden <jeremy@...zel.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Bixuan Cui <cuibixuan@...ux.alibaba.com>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Leon Romanovsky <leon@...nel.org>, Willy Tarreau <w@....eu>,
        Kees Cook <keescook@...omium.org>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Kicinski <kuba@...nel.org>, kvm@...r.kernel.org,
        netfilter-devel <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH -next] mm: delete oversized WARN_ON() in kvmalloc() calls

On Thu, Dec 2, 2021 at 2:38 AM Jeremy Sowden <jeremy@...zel.net> wrote:
>
> On 2021-12-01, at 20:29:05 -0800, Andrew Morton wrote:
> > On Thu, 2 Dec 2021 12:05:15 +0800 Bixuan Cui wrote:
> > > 在 2021/12/2 上午11:26, Andrew Morton 写道:
> > > >> Delete the WARN_ON() and return NULL directly for oversized
> > > >> parameter in kvmalloc() calls.
> > > >> Also add unlikely().
> > > >>
> > > >> Fixes: 7661809d493b ("mm: don't allow oversized kvmalloc() calls")
> > > >> Signed-off-by: Bixuan Cui<cuibixuan@...ux.alibaba.com>
> > > >> ---
> > > >> There are a lot of oversize warnings and patches about kvmalloc()
> > > >> calls recently. Maybe these warnings are not very necessary.
> > > >
> > > > Or maybe they are.  Please let's take a look at these warnings,
> > > > one at a time.  If a large number of them are bogus then sure,
> > > > let's disable the runtime test.  But perhaps it's the case that
> > > > calling code has genuine issues and should be repaired.
> > >
> > > Such as：
> >
> > Thanks, that's helpful.
> >
> > Let's bring all these to the attention of the relevant developers.
> >
> > If the consensus is "the code's fine, the warning is bogus" then let's
> > consider retiring the warning.
> >
> > If the consensus is otherwise then hopefully they will fix their stuff!
> >
> > > https://syzkaller.appspot.com/bug?id=24452f89446639c901ac07379ccc702808471e8e
> >
> > (cc bpf@...r.kernel.org)
> >
> > > https://syzkaller.appspot.com/bug?id=f7c5a86e747f9b7ce333e7295875cd4ede2c7a0d
> >
> > (cc netdev@...r.kernel.org, maintainers)
> >
> > > https://syzkaller.appspot.com/bug?id=8f306f3db150657a1f6bbe1927467084531602c7
> >
> > (cc kvm@...r.kernel.org)
> >
> > > https://syzkaller.appspot.com/bug?id=6f30adb592d476978777a1125d1f680edfc23e00
> >
> > (cc netfilter-devel@...r.kernel.org)
>
> The netfilter bug has since been fixed:
>
>   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/?id=7bbc3d385bd813077acaf0e6fdb2a86a901f5382

How is this a "fix" ?
u32 was the limit and because of the new warn the limit
got reduced to s32.
Every subsystem is supposed to do this "fix" now?

> > > https://syzkaller.appspot.com/bug?id=4c9ab8c7d0f8b551950db06559dc9cde4119ac83
> >
> > (bpf again).
>
> J.