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

Herbert Xu
2022-09-01T07:50:22Z

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@gondor.apana.org.au>
> Reported-by: syzbot+5ec9bb042ddfe9644773@syzkaller.appspotmail.com
> Tested-by: syzbot+5ec9bb042ddfe9644773@syzkaller.appspotmail.com
> Signed-off-by: Khalid Masum <khalid.masum.92@gmail.com>

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

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