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

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Message-ID: <CAHC9VhSmZvxkmjeUuYyUZjKDLGpacweLod7rnmeYrWwZH444Sg@mail.gmail.com>
Date: Tue, 12 Mar 2024 19:17:13 -0400
From: Paul Moore <paul@...l-moore.com>
To: Casey Schaufler <casey@...aufler-ca.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
Subject: Re: [PATCH v15 05/11] LSM: Create lsm_list_modules system call

On Tue, Mar 12, 2024 at 6:18 PM Casey Schaufler <casey@...aufler-cacom> wrote:
> On 3/12/2024 3:06 PM, Paul Moore wrote:
> > On Tue, Mar 12, 2024 at 2:28 PM Dmitry V. Levin <ldv@...ace.io> wrote:
> >> On Tue, Mar 12, 2024 at 10:44:38AM -0700, Casey Schaufler wrote:
> >>> 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?
> >> As lsm_get_self_attr() has the same issue, it needs the same treatment.
> >>
> >> lsm_set_self_attr() could be left unchanged.  In fact, changing the type
> >> of syscall arguments from size_t to an explicit 64-bit type would be
> >> problematic because 32-bit syscalls cannot have 64-bit arguments.
> > You might as well convert all of the size_t parameters, pointers or
> > otherwise, in the three syscalls to u32 Casey.
>
> Well, nuts. So much for that coin flip. V2 coming real soon.

Yeah, sorry for the false starts today ...

-- 
paul-moore.com