Re: [PATCH v30 08/12] landlock: Add syscall implementations

Mickaël Salaün
2021-03-24T15:04:08Z

On 19/03/2021 22:53, Mickaël Salaün wrote:
>
> On 19/03/2021 20:06, Kees Cook wrote:
>> On Tue, Mar 16, 2021 at 09:42:48PM +0100, Mickaël Salaün wrote:
>>> From: Mickaël Salaün <mic@linux.microsoft.com>

[...]

>>> +/**
>>> + * sys_landlock_create_ruleset - Create a new ruleset
>>> + *
>>> + * @attr: Pointer to a &struct landlock_ruleset_attr identifying the scope of
>>> + * the new ruleset.
>>> + * @size: Size of the pointed &struct landlock_ruleset_attr (needed for
>>> + * backward and forward compatibility).
>>> + * @flags: Must be 0.
>>> + *
>>> + * This system call enables to create a new Landlock ruleset, and returns the
>>> + * related file descriptor on success.
>>> + *
>>> + * Possible returned errors are:
>>> + *
>>> + * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
>>> + * - EINVAL: @flags is not 0, or unknown access, or too small @size;
>>> + * - E2BIG or EFAULT: @attr or @size inconsistencies;
>>> + * - ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
>>> + */
>>> +SYSCALL_DEFINE3(landlock_create_ruleset,
>>> + const struct landlock_ruleset_attr __user *const, attr,
>>> + const size_t, size, const __u32, flags)
>>> +{
>>> + struct landlock_ruleset_attr ruleset_attr;
>>> + struct landlock_ruleset *ruleset;
>>> + int err, ruleset_fd;
>>> +
>>> + /* Build-time checks. */
>>> + build_check_abi();
>>> +
>>> + if (!landlock_initialized)
>>> + return -EOPNOTSUPP;
>>> +
>>> + /* No flag for now. */
>>> + if (flags)
>>> + return -EINVAL;
>>> +
>>> + /* Copies raw user space buffer. */
>>> + err = copy_min_struct_from_user(&ruleset_attr, sizeof(ruleset_attr),
>>> + offsetofend(typeof(ruleset_attr), handled_access_fs),
>>
>> The use of offsetofend() here appears to be kind of the "V1", "V2", ...
>> sizes used in other extensible syscall implementations?
>
> ruleset_attr is an extensible argument.

offsetofen() is used to set the minimum size of a valid argument. This
code will then not change with future extended ruleset_attr.