linux-kernel - Re: [PATCH V4] audit: add tty field to LOGIN event

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Message-ID: <2689878.2iyKlAmhn2@x2>
Date:	Fri, 22 Apr 2016 09:13:18 -0400
From:	Steve Grubb <sgrubb@...hat.com>
To:	linux-audit@...hat.com
Cc:	Paul Moore <paul@...l-moore.com>,
	Richard Guy Briggs <rgb@...hat.com>,
	linux-kernel@...r.kernel.org, peter@...leysoftware.com
Subject: Re: [PATCH V4] audit: add tty field to LOGIN event

On Thursday, April 21, 2016 09:29:57 PM Paul Moore wrote:
> On Thu, Apr 21, 2016 at 2:14 PM, Richard Guy Briggs <rgb@...hat.com> wrote:
> > The tty field was missing from AUDIT_LOGIN events.
> > 
> > Refactor code to create a new function audit_get_tty(), using it to
> > replace the call in audit_log_task_info() and to add it to
> > audit_log_set_loginuid().  Lock and bump the kref to protect it, adding
> > audit_put_tty() alias to decrement it.
> > 
> > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > ---
> > 
> > V4: Add missing prototype for audit_put_tty() when audit syscall is not
> > 
> >     enabled (MIPS).
> > 
> > V3: Introduce audit_put_tty() alias to decrement kref.
> > 
> > V2: Use kref to protect tty signal struct while in use.
> > 
> > ---
> > 
> >  include/linux/audit.h |   24 ++++++++++++++++++++++++
> >  kernel/audit.c        |   18 +++++-------------
> >  kernel/auditsc.c      |    8 ++++++--
> >  3 files changed, 35 insertions(+), 15 deletions(-)
> > 
> > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > index b40ed5d..32cdafb 100644
> > --- a/include/linux/audit.h
> > +++ b/include/linux/audit.h
> > @@ -26,6 +26,7 @@
> > 
> >  #include <linux/sched.h>
> >  #include <linux/ptrace.h>
> >  #include <uapi/linux/audit.h>
> > 
> > +#include <linux/tty.h>
> > 
> >  #define AUDIT_INO_UNSET ((unsigned long)-1)
> >  #define AUDIT_DEV_UNSET ((dev_t)-1)
> > 
> > @@ -343,6 +344,23 @@ static inline unsigned int audit_get_sessionid(struct
> > task_struct *tsk)> 
> >         return tsk->sessionid;
> >  
> >  }
> > 
> > +static inline struct tty_struct *audit_get_tty(struct task_struct *tsk)
> > +{
> > +       struct tty_struct *tty = NULL;
> > +       unsigned long flags;
> > +
> > +       spin_lock_irqsave(&tsk->sighand->siglock, flags);
> > +       if (tsk->signal)
> > +               tty = tty_kref_get(tsk->signal->tty);
> > +       spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
> > +       return tty;
> > +}
> > +
> > +static inline void audit_put_tty(struct tty_struct *tty)
> > +{
> > +       tty_kref_put(tty);
> > +}
> 
> I'm generally not a big fan of defining functions as inlines in header
> files, with the general exception of dummy functions that will get
> compiled out.  Although I guess there might be some performance
> argument to be made wrt audit_log_task_info().
> 
> I guess I'm fine with this, but what was the idea behind the static
> inlines in audit.h?  Performance, or something else?

I think that is normal to prevent multiple definitions at link time.


> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index 195ffae..71e14d8 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -1980,6 +1980,7 @@ static void audit_log_set_loginuid(kuid_t
> > koldloginuid, kuid_t kloginuid,> 
> >  {
> >  
> >         struct audit_buffer *ab;
> >         uid_t uid, oldloginuid, loginuid;
> > 
> > +       struct tty_struct *tty;
> > 
> >         if (!audit_enabled)
> >         
> >                 return;
> > 
> > @@ -1987,14 +1988,17 @@ static void audit_log_set_loginuid(kuid_t
> > koldloginuid, kuid_t kloginuid,> 
> >         uid = from_kuid(&init_user_ns, task_uid(current));
> >         oldloginuid = from_kuid(&init_user_ns, koldloginuid);
> >         loginuid = from_kuid(&init_user_ns, kloginuid),
> > 
> > +       tty = audit_get_tty(current);
> > 
> >         ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_LOGIN);
> >         if (!ab)
> >         
> >                 return;
> >         
> >         audit_log_format(ab, "pid=%d uid=%u", task_pid_nr(current), uid);
> >         audit_log_task_context(ab);
> > 
> > -       audit_log_format(ab, " old-auid=%u auid=%u old-ses=%u ses=%u
> > res=%d", -                        oldloginuid, loginuid, oldsessionid,
> > sessionid, !rc); +       audit_log_format(ab, " old-auid=%u auid=%u
> > tty=%s old-ses=%u ses=%u res=%d", +                        oldloginuid,
> > loginuid, tty ? tty_name(tty) : "(none)", +                       
> > oldsessionid, sessionid, !rc);
> > +       audit_put_tty(tty);
> > 
> >         audit_log_end(ab);
> >  
> >  }
> 
> Because we are still using the crappy fixed string format for
> kernel<->userspace communication, this patch will likely "break the
> world" ... let's check with Steve but I believe the way to handle this
> is to add the tty information to the end of the record.

The placement is OK. Thanks for asking.

-Steve