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Message-ID: <20130509135247.GF7402@madcap2.tricolour.ca>
Date:	Thu, 9 May 2013 09:52:47 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Steve Grubb <sgrubb@...hat.com>
Cc:	linux-audit@...hat.com,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH] [BZ905179] audit: omit check for uid and gid validity in
 audit rules and data

On Thu, May 09, 2013 at 09:29:18AM -0400, Steve Grubb wrote:
> On Tuesday, April 16, 2013 03:38:23 PM Richard Guy Briggs wrote:
> > On Tue, Apr 09, 2013 at 02:39:32AM -0700, Eric W. Biederman wrote:
> > > Andrew Morton <akpm@...ux-foundation.org> writes:
> > > > On Wed, 20 Mar 2013 15:18:17 -0400 Richard Guy Briggs <rgb@...hat.com> 
> wrote:
> > > >> audit rule additions containing "-F auid!=4294967295" were failing with
> > > >> EINVAL.> 
> > > The only case where this appears to make the least little bit of sense
> > > is if the goal of the test is to test to see if an audit logloginuid
> > > has been set at all.  In which case depending on a test against
> > > 4294967295 is bogus because you are depending on an intimate internal
> > > kernel implementation detail.
> > > 
> > > How about something like my untested patch below that add an explicit
> > > operation to test if loginuid has been set?
> > 
> > Sorry for the delay in testing this, I had another urgent bug and a
> > belligerent test box...
> > 
> > I like this approach better than mine now that I understand it.  I've
> > tested the patch below without any changes.  It works as expected with
> > my previous test case.  I don't know if a Signed-off-by: is appropriate
> > for me in this case, but I'll throw in a:
> > 
> > Tested-by: Richard Guy Briggs <rbriggs@...hat.com>
> > 
> > and recommend a:
> > 
> > Reported-By: Steve Grubb <sbrubb@...hat.com>
> 
> If this is the approved patch, can it be put in stable? The audit system 
> hasn't worked as intended since January.

Most certainly.  I should have added that.  I only thought about that
after sending.

> Thanks,
> -Steve
> 
> > > From: "Eric W. Biederman" <ebiederm@...ssion.com>
> > > Date: Tue, 9 Apr 2013 02:22:10 -0700
> > > Subject: [PATCH] audit: Make testing for a valid loginuid explicit.
> > > 
> > > audit rule additions containing "-F auid!=4294967295" were failing
> > > with EINVAL.
> > > 
> > > Apparently some userland audit rule sets want to know if loginuid uid
> > > has been set and are using a test for auid != 4294967295 to determine
> > > that.
> > > 
> > > In practice that is a horrible way to ask if a value has been set,
> > > because it relies on subtle implementation details and will break
> > > every time the uid implementation in the kernel changes.
> > > 
> > > So add a clean way to test if the audit loginuid has been set, and
> > > silently convert the old idiom to the cleaner and more comprehensible
> > > new idiom.
> > > 
> > > Reported-By: Richard Guy Briggs <rgb@...hat.com> wrote:
> > > Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> > > ---
> > > 
> > >  include/linux/audit.h      |    5 +++++
> > >  include/uapi/linux/audit.h |    1 +
> > >  kernel/auditfilter.c       |   29 +++++++++++++++++++++++++++++
> > >  kernel/auditsc.c           |    5 ++++-
> > >  4 files changed, 39 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > > index a9fefe2..8a1ddde 100644
> > > --- a/include/linux/audit.h
> > > +++ b/include/linux/audit.h
> > > @@ -390,6 +390,11 @@ static inline void audit_ptrace(struct task_struct
> > > *t)
> > > 
> > >  #define audit_signals 0
> > >  #endif /* CONFIG_AUDITSYSCALL */
> > > 
> > > +static inline bool audit_loginuid_set(struct task_struct *tsk)
> > > +{
> > > +	return uid_valid(audit_get_loginuid(tsk));
> > > +}
> > > +
> > > 
> > >  #ifdef CONFIG_AUDIT
> > >  /* These are defined in audit.c */
> > >  
> > >  				/* Public API */
> > > 
> > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > > index 9f096f1..9554a19 100644
> > > --- a/include/uapi/linux/audit.h
> > > +++ b/include/uapi/linux/audit.h
> > > @@ -246,6 +246,7 @@
> > > 
> > >  #define AUDIT_OBJ_TYPE	21
> > >  #define AUDIT_OBJ_LEV_LOW	22
> > >  #define AUDIT_OBJ_LEV_HIGH	23
> > > 
> > > +#define AUDIT_LOGINUID_SET	24
> > > 
> > >  				/* These are ONLY useful when checking
> > >  				
> > >  				 * at syscall exit time (AUDIT_AT_EXIT). */
> > > 
> > > diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> > > index 540f986..6381d17 100644
> > > --- a/kernel/auditfilter.c
> > > +++ b/kernel/auditfilter.c
> > > @@ -349,6 +349,12 @@ static struct audit_entry *audit_rule_to_entry(struct
> > > audit_rule *rule)> 
> > >  		if (f->op == Audit_bad)
> > >  		
> > >  			goto exit_free;
> > > 
> > > +		/* Support legacy tests for a valid loginuid */
> > > +		if ((f->type == AUDIT_LOGINUID) && (f->val == 4294967295)) {
> > > +			f->type = AUDIT_LOGINUID_SET;
> > > +			f->val = 0;
> > > +		}
> > > +
> > > 
> > >  		switch(f->type) {
> > >  		
> > >  		default:
> > >  			goto exit_free;
> > > 
> > > @@ -377,6 +383,12 @@ static struct audit_entry *audit_rule_to_entry(struct
> > > audit_rule *rule)> 
> > >  			if (!gid_valid(f->gid))
> > >  			
> > >  				goto exit_free;
> > >  			
> > >  			break;
> > > 
> > > +		case AUDIT_LOGINUID_SET:
> > > +			if ((f->op != Audit_not_equal) && (f->op != Audit_equal))
> > > +				goto exit_free;
> > > +			if ((f->val != 0) && (f->val != 1))
> > > +				goto exit_free;
> > > +			break;
> > > 
> > >  		case AUDIT_PID:
> > >  		case AUDIT_PERS:
> > > 
> > >  		case AUDIT_MSGTYPE:
> > > @@ -459,6 +471,13 @@ static struct audit_entry *audit_data_to_entry(struct
> > > audit_rule_data *data,> 
> > >  		f->gid = INVALID_GID;
> > >  		f->lsm_str = NULL;
> > >  		f->lsm_rule = NULL;
> > > 
> > > +
> > > +		/* Support legacy tests for a valid loginuid */
> > > +		if ((f->type == AUDIT_LOGINUID) && (f->val == 4294967295)) {
> > > +			f->type = AUDIT_LOGINUID_SET;
> > > +			f->val = 0;
> > > +		}
> > > +
> > > 
> > >  		switch(f->type) {
> > >  		case AUDIT_UID:
> > > 
> > >  		case AUDIT_EUID:
> > > @@ -487,6 +506,12 @@ static struct audit_entry *audit_data_to_entry(struct
> > > audit_rule_data *data,> 
> > >  			if (!gid_valid(f->gid))
> > >  			
> > >  				goto exit_free;
> > >  			
> > >  			break;
> > > 
> > > +		case AUDIT_LOGINUID_SET:
> > > +			if ((f->op != Audit_not_equal) && (f->op != Audit_equal))
> > > +				goto exit_free;
> > > +			if ((f->val != 0) && (f->val != 1))
> > > +				goto exit_free;
> > > +			break;
> > > 
> > >  		case AUDIT_PID:
> > >  		case AUDIT_PERS:
> > > 
> > >  		case AUDIT_MSGTYPE:
> > > @@ -1380,6 +1405,10 @@ static int audit_filter_user_rules(struct
> > > audit_krule *rule,> 
> > >  			result = audit_uid_comparator(audit_get_loginuid(current),
> > >  			
> > >  						  f->op, f->uid);
> > >  			
> > >  			break;
> > > 
> > > +		case AUDIT_LOGINUID_SET:
> > > +			result = audit_comparator(audit_loginuid_set(current),
> > > +						  f->op, f->val);
> > > +			break;
> > > 
> > >  		case AUDIT_SUBJ_USER:
> > >  		case AUDIT_SUBJ_ROLE:
> > > 
> > >  		case AUDIT_SUBJ_TYPE:
> > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > > index 3a11d34..27d0a50 100644
> > > --- a/kernel/auditsc.c
> > > +++ b/kernel/auditsc.c
> > > @@ -750,6 +750,9 @@ static int audit_filter_rules(struct task_struct *tsk,
> > > 
> > >  			if (ctx)
> > >  			
> > >  				result = audit_uid_comparator(tsk->loginuid, f->op, 
> f->uid);
> > >  			
> > >  			break;
> > > 
> > > +		case AUDIT_LOGINUID_SET:
> > > +			result = audit_comparator(audit_loginuid_set(tsk), f->op, 
> f->val);
> > > +			break;
> > > 
> > >  		case AUDIT_SUBJ_USER:
> > >  		case AUDIT_SUBJ_ROLE:
> > > 
> > >  		case AUDIT_SUBJ_TYPE:
> > > @@ -2317,7 +2320,7 @@ int audit_set_loginuid(kuid_t loginuid)
> > > 
> > >  	unsigned int sessionid;
> > >  
> > >  #ifdef CONFIG_AUDIT_LOGINUID_IMMUTABLE
> > > 
> > > -	if (uid_valid(task->loginuid))
> > > +	if (audit_loginuid_set(task))
> > > 
> > >  		return -EPERM;
> > >  
> > >  #else /* CONFIG_AUDIT_LOGINUID_IMMUTABLE */
> > >  
> > >  	if (!capable(CAP_AUDIT_CONTROL))
> > 
> > - RGB
> > 
> > --
> > Richard Guy Briggs <rbriggs@...hat.com>
> > Senior Software Engineer
> > AMER ENG Base Operating Systems
> > Remote, Canada, Ottawa
> > Voice: 1.647.777.2635
> > Internal: (81) 32635
> > 
> > --
> > Linux-audit mailing list
> > Linux-audit@...hat.com
> > https://www.redhat.com/mailman/listinfo/linux-audit

- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer
AMER ENG Base Operating Systems
Remote, Ottawa, Canada
Voice: 1.647.777.2635
Internal: (81) 32635
--
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