linux-kernel - Re: [PATCH 6/7] lkdtm: crash on overwriting protected pmalloc var

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Message-ID: <1120e8fd-2f48-5b1f-7072-9bd8e2b82fbf@gmail.com>
Date:   Tue, 6 Mar 2018 09:05:00 -0800
From:   J Freyensee <why2jjj.linux@...il.com>
To:     Igor Stoppa <igor.stoppa@...wei.com>, david@...morbit.com,
        willy@...radead.org, keescook@...omium.org, mhocko@...nel.org
Cc:     labbott@...hat.com, linux-security-module@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 6/7] lkdtm: crash on overwriting protected pmalloc var


>   
> +#ifdef CONFIG_PROTECTABLE_MEMORY
> +void lkdtm_WRITE_RO_PMALLOC(void)
> +{
> +	struct gen_pool *pool;
> +	int *i;
> +
> +	pool = pmalloc_create_pool("pool", 0);
> +	if (unlikely(!pool)) {
> +		pr_info("Failed preparing pool for pmalloc test.");
> +		return;
> +	}
> +
> +	i = (int *)pmalloc(pool, sizeof(int), GFP_KERNEL);
> +	if (unlikely(!i)) {
> +		pr_info("Failed allocating memory for pmalloc test.");
> +		pmalloc_destroy_pool(pool);
> +		return;
> +	}
> +
> +	*i = INT_MAX;
> +	pmalloc_protect_pool(pool);
> +
> +	pr_info("attempting bad pmalloc write at %p\n", i);
> +	*i = 0;

Seems harmless, but I don't get why *i local variable needs to be set to 
0 at the end of this function.


Otherwise,

Reviewed-by: Jay Freyensee <why2jjj.linux@...il.com>