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

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Message-ID: <f122b3a9-1208-4c0b-9289-73eb070a8337@schaufler-ca.com>
Date: Tue, 12 Mar 2024 08:27:49 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: Paul Moore <paul@...l-moore.com>, "Dmitry V. Levin" <ldv@...ace.io>
Cc: 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 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.

>
> Thanks all.
>