linux-kernel - Re: [PATCH v15 05/11] LSM: Create lsm_list

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Date: Tue, 12 Mar 2024 10:44:38 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: Paul Moore <paul@...l-moore.com>
Cc: "Dmitry V. Levin" <ldv@...ace.io>, linux-security-module@...r.kernel.org,
 jmorris@...ei.org, serge@...lyn.com, keescook@...omium.org,
 john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
 stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
 linux-api@...r.kernel.org, mic@...ikod.net,
 Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v15 05/11] LSM: Create lsm_list_modules system call

On 3/12/2024 10:06 AM, Paul Moore wrote:
> On Tue, Mar 12, 2024 at 11:27 AM Casey Schaufler <casey@...aufler-ca.com> wrote:
>> On 3/12/2024 6:25 AM, Paul Moore wrote:
>>> On Tue, Mar 12, 2024 at 6:16 AM Dmitry V. Levin <ldv@...ace.io> wrote:
>>>> On Tue, Sep 12, 2023 at 01:56:50PM -0700, Casey Schaufler wrote:
>>>> [...]
>>>>> --- a/security/lsm_syscalls.c
>>>>> +++ b/security/lsm_syscalls.c
>>>>> @@ -55,3 +55,42 @@ SYSCALL_DEFINE4(lsm_get_self_attr, unsigned int, attr, struct lsm_ctx __user *,
>>>>>  {
>>>>>       return security_getselfattr(attr, ctx, size, flags);
>>>>>  }
>>>>> +
>>>>> +/**
>>>>> + * sys_lsm_list_modules - Return a list of the active security modules
>>>>> + * @ids: the LSM module ids
>>>>> + * @size: pointer to size of @ids, updated on return
>>>>> + * @flags: reserved for future use, must be zero
>>>>> + *
>>>>> + * Returns a list of the active LSM ids. On success this function
>>>>> + * returns the number of @ids array elements. This value may be zero
>>>>> + * if there are no LSMs active. If @size is insufficient to contain
>>>>> + * the return data -E2BIG is returned and @size is set to the minimum
>>>>> + * required size. In all other cases a negative value indicating the
>>>>> + * error is returned.
>>>>> + */
>>>>> +SYSCALL_DEFINE3(lsm_list_modules, u64 __user *, ids, size_t __user *, size,
>>>>> +             u32, flags)
>>>> I'm sorry but the size of userspace size_t is different from the kernel one
>>>> on 32-bit compat architectures.
>>> D'oh, yes, thanks for pointing that out.  It would have been nice to
>>> have caught that before v6.8 was released, but I guess it's better
>>> than later.
>>>
>>>> Looks like there has to be a COMPAT_SYSCALL_DEFINE3(lsm_list_modules, ..)
>>>> now.  Other two added lsm syscalls also have this issue.
>>> Considering that Linux v6.8, and by extension these syscalls, are only
>>> a few days old, I think I'd rather see us just modify the syscalls and
>>> avoid the compat baggage.  I'm going to be shocked if anyone has
>>> shifted to using the new syscalls yet, and even if they have (!!),
>>> moving from a "size_t" type to a "u64" should be mostly transparent
>>> for the majority of native 64-bit systems.  Those running the absolute
>>> latest kernels on 32-bit systems with custom or bleeding edge
>>> userspace *may* see a slight hiccup, but I think that user count is in
>>> the single digits, if not zero.
>>>
>>> Let's fix this quickly with /size_t/u64/ in v6.8.1 and avoid the
>>> compat shim if we can.
>>>
>>> Casey, do you have time to put together a patch for this (you should
>>> fix the call chains below the syscalls too)?  If not, please let me
>>> know and I'll get a patch out ASAP.
>> Grumble. Yes, I'll get right on it.
> Great, thanks Casey.

Look like lsm_get_self_attr() needs the same change. lsm_set_self_attr()
doesn't, need it, but I'm tempted to change it as well for consistency.
Thoughts?

>