linux-kernel - Re: [PATCH v2 1/1] mm: fix use-after-free when anon vma name is used after vma is freed

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Message-ID: <YgUSxzp/qDwLkiKb@casper.infradead.org>
Date:   Thu, 10 Feb 2022 13:27:35 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, ccross@...gle.com,
        sumit.semwal@...aro.org, mhocko@...e.com, dave.hansen@...el.com,
        keescook@...omium.org, kirill.shutemov@...ux.intel.com,
        vbabka@...e.cz, hannes@...xchg.org, ebiederm@...ssion.com,
        brauner@...nel.org, legion@...nel.org, ran.xiaokai@....com.cn,
        sashal@...nel.org, chris.hyser@...cle.com, dave@...olabs.net,
        pcc@...gle.com, caoxiaofeng@...ong.com, david@...hat.com,
        gorcunov@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        syzbot+aa7b3d4b35f9dc46a366@...kaller.appspotmail.com
Subject: Re: [PATCH v2 1/1] mm: fix use-after-free when anon vma name is used
 after vma is freed

On Wed, Feb 09, 2022 at 08:32:15PM -0800, Suren Baghdasaryan wrote:
> +void vma_anon_name_put(struct anon_vma_name *anon_name)
> +{
> +	kref_put(&anon_name->kref, vma_anon_name_free);
> +}

To agree with Michal, make this:

	if (anon_name)
		kref_put(&anon_name->kref, vma_anon_name_free);

>  
> -	error = madvise_update_vma(vma, prev, start, end, new_flags,
> -				   vma_anon_name(vma));
> +	anon_name = vma_anon_name_get(vma);
> +	if (anon_name) {
> +		error = madvise_update_vma(vma, prev, start, end, new_flags,
> +					   anon_name->name);
> +		vma_anon_name_put(anon_name);
> +	} else {
> +		error = madvise_update_vma(vma, prev, start, end, new_flags,
> +					   NULL);
> +	}

And then this becomes:

	anon_name = vma_anon_name_get(vma);
	error = madvise_update_vma(vma, prev, start, end, new_flags, anon_name);
	vma_anon_name_put(anon_name);