linux-kernel - Re: [PATCH v2 3/4] livepatch: Proper error handling in the shadow variables selftest

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Date:   Tue, 5 Feb 2019 16:17:13 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Petr Mladek <pmladek@...e.com>, Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>
Cc:     Jason Baron <jbaron@...mai.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] livepatch: Proper error handling in the shadow
 variables selftest

On 2/4/19 8:56 AM, Petr Mladek wrote:
> Add proper error handling when allocating or getting shadow variables
> in the selftest. It prevents an invalid pointer access in some situations.
> It shows the good programming practice in the others.
> 
> The error codes are just the best guess and specific for this particular
> test. In general, klp_shadow_alloc() returns NULL also when the given
> shadow variable has already been allocated. In addition, both
> klp_shadow_alloc() and klp_shadow_get_or_alloc() might fail from
> other reasons when the constructor fails.
> 
> Note, that the error code is not really important even in the real life.
> The use of shadow variables should be transparent for the original
> livepatched code.
> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> ---
>   lib/livepatch/test_klp_shadow_vars.c | 22 ++++++++++++++++++++++
>   1 file changed, 22 insertions(+)
> 
> diff --git a/lib/livepatch/test_klp_shadow_vars.c b/lib/livepatch/test_klp_shadow_vars.c
> index f5441c193166..fe5c413efe96 100644
> --- a/lib/livepatch/test_klp_shadow_vars.c
> +++ b/lib/livepatch/test_klp_shadow_vars.c
> @@ -154,22 +154,37 @@ static int test_klp_shadow_vars_init(void)
>   	 * Allocate a few shadow variables with different <obj> and <id>.
>   	 */
>   	sv1 = shadow_alloc(obj, id, size, gfp_flags, shadow_ctor, &var1);
> +	if (!sv1)
> +		return -ENOMEM;
> +
>   	sv2 = shadow_alloc(obj + 1, id, size, gfp_flags, shadow_ctor, &var2);
> +	if (!sv2)
> +		return -ENOMEM;
> +
>   	sv3 = shadow_alloc(obj, id + 1, size, gfp_flags, shadow_ctor, &var3);
> +	if (!sv3)
> +		return -ENOMEM;
>   
>   	/*
>   	 * Verify we can find our new shadow variables and that they point
>   	 * to expected data.
>   	 */
>   	ret = shadow_get(obj, id);
> +	if (!ret)
> +		return -EINVAL;
>   	if (ret == sv1 && *sv1 == &var1)
>   		pr_info("  got expected PTR%d -> PTR%d result\n",
>   			ptr_id(sv1), ptr_id(*sv1));
> +
>   	ret = shadow_get(obj + 1, id);
> +	if (!ret)
> +		return -EINVAL;
>   	if (ret == sv2 && *sv2 == &var2)
>   		pr_info("  got expected PTR%d -> PTR%d result\n",
>   			ptr_id(sv2), ptr_id(*sv2));
>   	ret = shadow_get(obj, id + 1);
> +	if (!ret)
> +		return -EINVAL;
>   	if (ret == sv3 && *sv3 == &var3)
>   		pr_info("  got expected PTR%d -> PTR%d result\n",
>   			ptr_id(sv3), ptr_id(*sv3));
> @@ -179,7 +194,12 @@ static int test_klp_shadow_vars_init(void)
>   	 * The second invocation should return the same shadow var.
>   	 */
>   	sv4 = shadow_get_or_alloc(obj + 2, id, size, gfp_flags, shadow_ctor, &var4);
> +	if (!sv4)
> +		return -ENOMEM;
> +
>   	ret = shadow_get_or_alloc(obj + 2, id, size, gfp_flags, shadow_ctor, &var4);
> +	if (!ret)
> +		return -EINVAL;
>   	if (ret == sv4 && *sv4 == &var4)
>   		pr_info("  got expected PTR%d -> PTR%d result\n",
>   			ptr_id(sv4), ptr_id(*sv4));
> @@ -207,6 +227,8 @@ static int test_klp_shadow_vars_init(void)
>   	 * We should still find an <id+1> variable.
>   	 */
>   	ret = shadow_get(obj, id + 1);
> +	if (!ret)
> +		return -EINVAL;
>   	if (ret == sv3 && *sv3 == &var3)
>   		pr_info("  got expected PTR%d -> PTR%d result\n",
>   			ptr_id(sv3), ptr_id(*sv3));
> 

Fixes look good to me,

Acked-by: Joe Lawrence <joe.lawrence@...hat.com>

-- Joe