linux-kernel - Re: [PATCH v3] xfrm: Update ipcomp_scratches with NULL if not allocated

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Date:   Thu, 1 Sep 2022 13:03:53 +0600
From:   Khalid Masum <khalid.masum.92@...il.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-kernel-mentees 
        <linux-kernel-mentees@...ts.linuxfoundation.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        syzbot+5ec9bb042ddfe9644773@...kaller.appspotmail.com
Subject: Re: [PATCH v3] xfrm: Update ipcomp_scratches with NULL if not allocated

On Thu, Sep 1, 2022 at 10:18 AM Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Thu, Sep 01, 2022 at 10:03:07AM +0600, Khalid Masum wrote:
> >
> > diff --git a/net/xfrm/xfrm_ipcomp.c b/net/xfrm/xfrm_ipcomp.c
> > index cb40ff0ff28d..3774d07c5819 100644
> > --- a/net/xfrm/xfrm_ipcomp.c
> > +++ b/net/xfrm/xfrm_ipcomp.c
> > @@ -203,6 +203,7 @@ static void ipcomp_free_scratches(void)
> >               vfree(*per_cpu_ptr(scratches, i));
> >
> >       free_percpu(scratches);
> > +     ipcomp_scratches = NULL;
> >  }
>
> Good catch! This is probably the root cause of all the crashes.
>
> >  static void * __percpu *ipcomp_alloc_scratches(void)
> > @@ -215,7 +216,7 @@ static void * __percpu *ipcomp_alloc_scratches(void)
> >
> >       scratches = alloc_percpu(void *);
> >       if (!scratches)
> > -             return NULL;
> > +             return ipcomp_scratches = NULL;
>
> This is unnecessary as with your first hunk, ipcomp_scratches
> is guaranteed to be NULL.
>
> Thanks,
> --

You are right. Instead of setting it to NULL at both places, it makes
more sense to
do it when memory is freed.

I shall send a v4 with the suggested change.

thanks,
 -- Khalid Masum