netdev - Re: [PATCH v4] xfrm: Update ipcomp_scratches with NULL when freed

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Message-ID: <YxBj0QAdRaVZCr9i@gondor.apana.org.au>
Date:   Thu, 1 Sep 2022 15:48:33 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Khalid Masum <khalid.masum.92@...il.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        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@...ts.linuxfoundation.org,
        Shuah Khan <skhan@...uxfoundation.org>,
        syzbot+5ec9bb042ddfe9644773@...kaller.appspotmail.com
Subject: Re: [PATCH v4] xfrm: Update ipcomp_scratches with NULL when freed

On Thu, Sep 01, 2022 at 01:12:10PM +0600, Khalid Masum wrote:
> Currently if ipcomp_alloc_scratches() fails to allocate memory
> ipcomp_scratches holds obsolete address. So when we try to free the
> percpu scratches using ipcomp_free_scratches() it tries to vfree non
> existent vm area. Described below:
> 
> static void * __percpu *ipcomp_alloc_scratches(void)
> {
>         ...
>         scratches = alloc_percpu(void *);
>         if (!scratches)
>                 return NULL;
> ipcomp_scratches does not know about this allocation failure.
> Therefore holding the old obsolete address.
>         ...
> }
> 
> So when we free,
> 
> static void ipcomp_free_scratches(void)
> {
>         ...
>         scratches = ipcomp_scratches;
> Assigning obsolete address from ipcomp_scratches
> 
>         if (!scratches)
>                 return;
> 
>         for_each_possible_cpu(i)
>                vfree(*per_cpu_ptr(scratches, i));
> Trying to free non existent page, causing warning: trying to vfree
> existent vm area.
>         ...
> }
> 
> Fix this breakage by updating ipcomp_scrtches with NULL when scratches
> is freed
> 
> Suggested-by: Herbert Xu <herbert@...dor.apana.org.au>
> Reported-by: syzbot+5ec9bb042ddfe9644773@...kaller.appspotmail.com
> Tested-by: syzbot+5ec9bb042ddfe9644773@...kaller.appspotmail.com
> Signed-off-by: Khalid Masum <khalid.masum.92@...il.com>

Acked-by: Herbert Xu <herbert@...dor.apana.org.au>

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt