Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <00000000000092839d0581fd74ad@google.com> <20220901040307.4674-1-khalid.masum.92@gmail.com>
 <YxAyd6++6oWPu9L1@gondor.apana.org.au>
In-Reply-To: <YxAyd6++6oWPu9L1@gondor.apana.org.au>
From:   Khalid Masum <khalid.masum.92@gmail.com>
Date:   Thu, 1 Sep 2022 13:03:53 +0600
Message-ID: <CAABMjtGgv1GP0F9TJCMFN2psx7ok23BR9pEOyemWHeKvc_LfqA@mail.gmail.com>
Subject: Re: [PATCH v3] xfrm: Update ipcomp_scratches with NULL if not allocated
To:     Herbert Xu <herbert@gondor.apana.org.au>
Cc:     "open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Steffen Klassert <steffen.klassert@secunet.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        linux-kernel-mentees 
        <linux-kernel-mentees@lists.linuxfoundation.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        syzbot+5ec9bb042ddfe9644773@syzkaller.appspotmail.com
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Sep 1, 2022 at 10:18 AM Herbert Xu <herbert@gondor.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