linux-kernel - Re: [PATCH v3] LSM: use 32 bit compatible data types in LSM syscalls.

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Date: Thu, 14 Mar 2024 14:18:27 -0400
From: Paul Moore <paul@...l-moore.com>
To: "Dmitry V. Levin" <ldv@...ace.io>
Cc: Casey Schaufler <casey@...aufler-ca.com>, 
	LSM List <linux-security-module@...r.kernel.org>, 
	Linux kernel mailing list <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org, 
	Mickaël Salaün <mic@...ikod.net>, 
	James Morris <jmorris@...ei.org>, Serge Hallyn <serge@...lyn.com>, 
	John Johansen <john.johansen@...onical.com>, 
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, 
	Stephen Smalley <stephen.smalley.work@...il.com>
Subject: Re: [PATCH v3] LSM: use 32 bit compatible data types in LSM syscalls.

On Thu, Mar 14, 2024 at 2:01 PM Dmitry V. Levin <ldv@...ace.io> wrote:
> On Thu, Mar 14, 2024 at 11:30:53AM -0400, Paul Moore wrote:
> > On Wed, Mar 13, 2024 at 4:07 PM Paul Moore <paul@...l-moore.com> wrote:
> > > On Mar 13, 2024 Casey Schaufler <casey@...aufler-ca.com> wrote:
> > > >
> > > > LSM: use 32 bit compatible data types in LSM syscalls.
> > > >
> > > > Change the size parameters in lsm_list_modules(), lsm_set_self_attr()
> > > > and lsm_get_self_attr() from size_t to u32. This avoids the need to
> > > > have different interfaces for 32 and 64 bit systems.
> > > >
> > > > Cc: stable@...r.kernel.org
> > > > Fixes: a04a1198088a: ("LSM: syscalls for current process attributes")
> > > > Fixes: ad4aff9ec25f: ("LSM: Create lsm_list_modules system call")
> > > > Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> > > > Reported-and-reviewed-by: Dmitry V. Levin <ldv@...ace.io>
> > > > ---
> > > >  include/linux/lsm_hook_defs.h                        |  4 ++--
> > > >  include/linux/security.h                             |  8 ++++----
> > > >  security/apparmor/lsm.c                              |  4 ++--
> > > >  security/lsm_syscalls.c                              | 10 +++++-----
> > > >  security/security.c                                  | 12 ++++++------
> > > >  security/selinux/hooks.c                             |  4 ++--
> > > >  security/smack/smack_lsm.c                           |  4 ++--
> > > >  tools/testing/selftests/lsm/common.h                 |  6 +++---
> > > >  tools/testing/selftests/lsm/lsm_get_self_attr_test.c | 10 +++++-----
> > > >  tools/testing/selftests/lsm/lsm_list_modules_test.c  |  8 ++++----
> > > >  tools/testing/selftests/lsm/lsm_set_self_attr_test.c |  6 +++---
> > > >  11 files changed, 38 insertions(+), 38 deletions(-)
> > >
> > > Okay, this looks better, I'm going to merge this into lsm/stable-6.9
> > > and put it through the usual automated testing as well as a kselftest
> > > run to make sure everything there is still okay.  Assuming all goes
> > > well and no one raises any objections, I'll likely send this up to
> > > Linus tomorrow.
> >
> > I had to squash the code snippet below into the patch to address a
> > build problem identified by the kernel build robot.  I'm going to keep
> > Casey's sign-off and Dmitry's reported-reviewed tag as I feel this
> > change is minor, but if anyone has any objections please let me know
> > soon.
> >
> > [NOTE: cut-n-paste'd into email, likely whitespace damage, but you get the idea]
> >
> > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> > index 77eb9b0e7685..e619ac10cd23 100644
> > --- a/include/linux/syscalls.h
> > +++ b/include/linux/syscalls.h
> > @@ -960,10 +960,10 @@ asmlinkage long sys_cachestat(unsigned int fd,
> >                struct cachestat __user *cstat, unsigned int flags);
> > asmlinkage long sys_map_shadow_stack(unsigned long addr, unsigned long size, un
> > signed int flags);
> > asmlinkage long sys_lsm_get_self_attr(unsigned int attr, struct lsm_ctx *ctx,
> > -                                     size_t *size, __u32 flags);
> > +                                     u32 *size, u32 flags);
> > asmlinkage long sys_lsm_set_self_attr(unsigned int attr, struct lsm_ctx *ctx,
> > -                                     size_t size, __u32 flags);
> > -asmlinkage long sys_lsm_list_modules(u64 *ids, size_t *size, u32 flags);
> > +                                     u32 size, u32 flags);
> > +asmlinkage long sys_lsm_list_modules(u64 *ids, u32 *size, u32 flags);
>
> Fine with me, thanks.
>
> btw, with the change above, u32 will become about twice more popular
> in include/linux/syscalls.h than __u32.

I was looking at that when I was putting the patch together this
morning, trying to decide which was the "correct" choice between 'u32'
and '__u32' and wasn't able to find a good explanation of which is the
"right" option in this file.  Ultimately I went with 'u32' as I tend
to follow some old guidance of: '__u32' for userspace headers, 'u32'
for kernel headers.

If it should be the other way, please let me know.  I just want to
keep it consistent across the LSM syscalls.

-- 
paul-moore.com