Re: [PATCH 23/28] security: Introduce LSM_ORDER_LAST

[Mimi Zohar <zohar@linux.ibm.com>]

On Wed, 2023-03-08 at 14:26 +0100, Roberto Sassu wrote:
> On Wed, 2023-03-08 at 08:13 -0500, Mimi Zohar wrote:
> > Hi Roberto,
> > 
> > On Fri, 2023-03-03 at 19:25 +0100, Roberto Sassu wrote:
> > > From: Roberto Sassu <roberto.sassu@huawei.com>
> > > 
> > > Introduce LSM_ORDER_LAST, to satisfy the requirement of LSMs willing to be
> > > the last, e.g. the 'integrity' LSM, without changing the kernel command
> > > line or configuration.
> > 
> > Please reframe this as a bug fix for 79f7865d844c ("LSM: Introduce
> > "lsm=" for boottime LSM selection") and upstream it first, with
> > 'integrity' as the last LSM.   The original bug fix commit 92063f3ca73a
> > ("integrity: double check iint_cache was initialized") could then be
> > removed.
> 
> Ok, I should complete the patch by checking the cache initialization in
> iint.c.
> 
> > > As for LSM_ORDER_FIRST, LSMs with LSM_ORDER_LAST are always enabled and put
> > > at the end of the LSM list in no particular order.
> > 
> > ^Similar to LSM_ORDER_FIRST ...
> > 
> > And remove "in no particular order".
> 
> The reason for this is that I originally thought that the relative
> order of LSMs specified in the kernel configuration or the command line
> was respected (if more than one LSM specifies LSM_ORDER_LAST). In fact
> not. To do this, we would have to parse the LSM string again, as it is
> done for LSM_ORDER_MUTABLE LSMs.

IMA and EVM are only configurable if 'integrity' is enabled.  Similar
to how LSM_ORDER_FIRST is reserved for capabilities, LSM_ORDER_LAST
should be reserved for integrity (LSMs), if it is configured, for the
reason as described in the "[PATCH 24/28] ima: Move to LSM
infrastructure" patch description.

> 
> Thanks
> 
> Roberto
> 
> > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > > ---
> > >  include/linux/lsm_hooks.h |  1 +
> > >  security/security.c       | 12 +++++++++---
> > >  2 files changed, 10 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> > > index 21a8ce23108..05c4b831d99 100644
> > > --- a/include/linux/lsm_hooks.h
> > > +++ b/include/linux/lsm_hooks.h
> > > @@ -93,6 +93,7 @@ extern void security_add_hooks(struct security_hook_list *hooks, int count,
> > >  enum lsm_order {
> > >  	LSM_ORDER_FIRST = -1,	/* This is only for capabilities. */
> > >  	LSM_ORDER_MUTABLE = 0,
> > > +	LSM_ORDER_LAST = 1,
> > >  };
> > >  
> > >  struct lsm_info {
> > > diff --git a/security/security.c b/security/security.c
> > > index 322090a50cd..24f52ba3218 100644
> > > --- a/security/security.c
> > > +++ b/security/security.c
> > > @@ -284,9 +284,9 @@ static void __init ordered_lsm_parse(const char *order, const char *origin)
> > >  		bool found = false;
> > >  
> > >  		for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
> > > -			if (lsm->order == LSM_ORDER_MUTABLE &&
> > > -			    strcmp(lsm->name, name) == 0) {
> > > -				append_ordered_lsm(lsm, origin);
> > > +			if (strcmp(lsm->name, name) == 0) {
> > > +				if (lsm->order == LSM_ORDER_MUTABLE)
> > > +					append_ordered_lsm(lsm, origin);
> > >  				found = true;
> > >  			}
> > >  		}
> > > @@ -306,6 +306,12 @@ static void __init ordered_lsm_parse(const char *order, const char *origin)
> > >  		}
> > >  	}
> > >  
> > > +	/* LSM_ORDER_LAST is always last. */
> > > +	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
> > > +		if (lsm->order == LSM_ORDER_LAST)
> > > +			append_ordered_lsm(lsm, "   last");
> > > +	}
> > > +
> > >  	/* Disable all LSMs not in the ordered list. */
> > >  	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
> > >  		if (exists_ordered_lsm(lsm))
>