linux-kernel - Re: [PATCH v38 39/39] LSM: Create lsm_module

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Date:   Wed, 12 Oct 2022 15:04:09 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     casey.schaufler@...el.com, paul@...l-moore.com,
        linux-security-module@...r.kernel.org, linux-audit@...hat.com,
        jmorris@...ei.org, selinux@...r.kernel.org,
        john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
        stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v38 39/39] LSM: Create lsm_module_list system call

On Tue, Sep 27, 2022 at 01:31:55PM -0700, Casey Schaufler wrote:
> +SYSCALL_DEFINE3(lsm_module_list,
> +	       unsigned int __user *, ids,
> +	       size_t __user *, size,
> +	       int, flags)

Please make this unsigned int.

> +{
> +	unsigned int *interum;
> +	size_t total_size = lsm_id * sizeof(*interum);
> +	size_t usize;
> +	int rc;
> +	int i;

Please test that flags == 0 so it can be used in the future:

	if (flags)
		return -EINVAL;

> +
> +	if (get_user(usize, size))
> +		return -EFAULT;
> +
> +	if (usize < total_size) {
> +		if (put_user(total_size, size) != 0)
> +			return -EFAULT;
> +		return -E2BIG;
> +	}
> +
> +	interum = kzalloc(total_size, GFP_KERNEL);
> +	if (interum == NULL)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < lsm_id; i++)
> +		interum[i] = lsm_idlist[i]->id;
> +
> +	if (copy_to_user(ids, interum, total_size) != 0 ||
> +	    put_user(total_size, size) != 0)
> +		rc = -EFAULT;

No need to repeat this, if it is written first.

> +	else
> +		rc = lsm_id;
> +
> +	kfree(interum);
> +	return rc;

No need for the alloc/free. Here's what I would imagine for the whole
thing:

	if (flags)
		return -EINVAL;

	if (get_user(usize, size))
		return -EFAULT;

	if (put_user(total_size, size) != 0)
		return -EFAULT;

	if (usize < total_size)
		return -E2BIG;

	for (i = 0; i < lsm_id; i++)
		if (put_user(lsm_idlist[i]->id, id++))
			return -EFAULT;

	return lsm_id;

-- 
Kees Cook