[PATCH] security: Add LSM hooks to set*gid syscalls

[Micah Morton]

On Fri, Jun 5, 2020 at 2:25 PM Kees Cook <keescook at chromium.org> wrote:
>
> On Fri, Jun 05, 2020 at 12:38:05PM -0700, Micah Morton wrote:
> > The SafeSetID LSM uses the security_task_fix_setuid hook to filter
> > set*uid() syscalls according to its configured security policy. In
> > preparation for adding analagous support in the LSM for set*gid()
> > syscalls, we add the requisite hook here. Tested by putting print
> > statements in the security_task_fix_setgid hook and seeing them get hit
> > during kernel boot.
> >
> > From: Thomas Cedeno <thomascedeno at google.com>
>
> ^^^ this line should be before the commit log body (many tools won't
> find it here).
>
> > Signed-off-by: Thomas Cedeno <thomascedeno at google.com>
> > Reviewed-by: Micah Morton <mortonm at chromium.org>
> > ---
> > NOTE: I (Micah) will send this patch as a pull request to Linus through
> > my SafeSetID tree if there are no objections.
> >  include/linux/lsm_hook_defs.h |  2 ++
> >  include/linux/lsm_hooks.h     |  9 +++++++++
> >  include/linux/security.h      |  9 +++++++++
> >  kernel/sys.c                  | 15 ++++++++++++++-
> >  security/security.c           |  6 ++++++
> >  5 files changed, 40 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> > index fb3ce6cec997..d5401c09f2d3 100644
> > --- a/include/linux/lsm_hook_defs.h
> > +++ b/include/linux/lsm_hook_defs.h
> > @@ -191,6 +191,8 @@ LSM_HOOK(int, 0, kernel_post_read_file, struct file *file, char *buf,
> >        loff_t size, enum kernel_read_file_id id)
> >  LSM_HOOK(int, 0, task_fix_setuid, struct cred *new, const struct cred *old,
> >        int flags)
> > +LSM_HOOK(int, 0, task_fix_setgid, struct cred *new, const struct cred * old,
> > +      int flags)
> >  LSM_HOOK(int, 0, task_setpgid, struct task_struct *p, pid_t pgid)
> >  LSM_HOOK(int, 0, task_getpgid, struct task_struct *p)
> >  LSM_HOOK(int, 0, task_getsid, struct task_struct *p)
> > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> > index 3e62dab77699..8012b610fe53 100644
> > --- a/include/linux/lsm_hooks.h
> > +++ b/include/linux/lsm_hooks.h
> > @@ -659,6 +659,15 @@
> >   *   @old is the set of credentials that are being replaces
> >   *   @flags contains one of the LSM_SETID_* values.
> >   *   Return 0 on success.
> > + * @task_fix_setgid:
> > + *     Update the module's state after setting one or more of the group
> > + *     identity attributes of the current process.  The @flags parameter
> > + *     indicates which of the set*gid system calls invoked this hook.
> > + *     @new is the set of credentials that will be installed.  Modifications
> > + *     should be made to this rather than to @current->cred.
> > + *     @old is the set of credentials that are being replaced.
> > + *     @flags contains one of the LSM_SETID_* values.
> > + *     Return 0 on success.
>
> The indenting here appears to be using spaces instead of a tab.
>
> Everything else looks okay. (There are a surprising number of gid
> changing places...)

Ah thanks! I'll fix those 2 things before doing the pull request.
Probably not worth doing a patch resend.

Will still give it some time to see if anyone else wants to comment.

>
> --
> Kees Cook