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

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Message-ID: <20160418182700.GD4577@madcap2.tricolour.ca>
Date:	Mon, 18 Apr 2016 14:27:00 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	sgrubb@...hat.com, pmoore@...hat.com, eparis@...hat.com
Subject: Re: [PATCH] audit: add tty field to LOGIN event

On 16/04/13, Peter Hurley wrote:
> Hi Richard,

Hi Peter,

> On 04/13/2016 04:25 PM, Richard Guy Briggs 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().
> > 
> > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > ---
> >  include/linux/audit.h |   18 ++++++++++++++++++
> >  kernel/audit.c        |   11 +----------
> >  kernel/auditsc.c      |    5 +++--
> >  3 files changed, 22 insertions(+), 12 deletions(-)
> > 
> > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > index b40ed5d..20c6649 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 +344,19 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
> >  	return tsk->sessionid;
> >  }
> >  
> > +static inline char *audit_get_tty(struct task_struct *tsk)
> > +{
> > +	char *tty;
> > +
> > +	spin_lock_irq(&tsk->sighand->siglock);
> > +	if (tsk->signal && tsk->signal->tty && tsk->signal->tty->name)
> > +		tty = tsk->signal->tty->name;
> > +	else
> > +		tty = "(none)";
> > +	spin_unlock_irq(&tsk->sighand->siglock);
> 
> This is unsafe because the tty could be immediately torn down after the
> siglock is dropped, and return a dangling ptr.

Understood.  The other option is to copy the value out...
Thanks for the helpful review.  Rev 2 coming...

> > +	return tty;
> > +}
> > +
> >  extern void __audit_ipc_obj(struct kern_ipc_perm *ipcp);
> >  extern void __audit_ipc_set_perm(unsigned long qbytes, uid_t uid, gid_t gid, umode_t mode);
> >  extern void __audit_bprm(struct linux_binprm *bprm);
> > @@ -500,6 +514,10 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
> >  {
> >  	return -1;
> >  }
> > +static inline char *audit_get_tty(struct task_struct *tsk)
> > +{
> > +	return "(invalid)";
> > +}
> >  static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
> >  { }
> >  static inline void audit_ipc_set_perm(unsigned long qbytes, uid_t uid,
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index 3a3e5de..fae11df 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -64,7 +64,6 @@
> >  #include <linux/security.h>
> >  #endif
> >  #include <linux/freezer.h>
> > -#include <linux/tty.h>
> >  #include <linux/pid_namespace.h>
> >  #include <net/netns/generic.h>
> >  
> > @@ -1873,7 +1872,6 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
> >  {
> >  	const struct cred *cred;
> >  	char comm[sizeof(tsk->comm)];
> > -	char *tty;
> 
> 	struct tty_struct *tty;
> 
> >  
> >  	if (!ab)
> >  		return;
> > @@ -1881,13 +1879,6 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
> >  	/* tsk == current */
> >  	cred = current_cred();
> >  
> > -	spin_lock_irq(&tsk->sighand->siglock);
> > -	if (tsk->signal && tsk->signal->tty && tsk->signal->tty->name)
> > -		tty = tsk->signal->tty->name;
> > -	else
> > -		tty = "(none)";
> > -	spin_unlock_irq(&tsk->sighand->siglock);
> 
> 	tty = get_current_tty();
> 	
> > -
> >  	audit_log_format(ab,
> >  			 " ppid=%d pid=%d auid=%u uid=%u gid=%u"
> >  			 " euid=%u suid=%u fsuid=%u"
> > @@ -1903,7 +1894,7 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
> >  			 from_kgid(&init_user_ns, cred->egid),
> >  			 from_kgid(&init_user_ns, cred->sgid),
> >  			 from_kgid(&init_user_ns, cred->fsgid),
> > -			 tty, audit_get_sessionid(tsk));
> > +			 audit_get_tty(tsk), audit_get_sessionid(tsk));
> 
> 			tty_name(tty), ....);
> 			^^^^^^^^^^
> 			returns "NULL tty" if tty == NULL
> 
> 	tty_kref_put(tty);
> 
> 
> >  
> >  	audit_log_format(ab, " comm=");
> >  	audit_log_untrustedstring(ab, get_task_comm(comm, tsk));
> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index 195ffae..a0467fb 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -1993,8 +1993,9 @@ static void audit_log_set_loginuid(kuid_t koldloginuid, kuid_t kloginuid,
> >  		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);
> 
> 	tty = get_current_tty();
> 
> > +	audit_log_format(ab, " old-auid=%u auid=%u tty=%s old-ses=%u ses=%u res=%d",
> > +			 oldloginuid, loginuid, audit_get_tty(current),
> 
> 			......., tty_name(tty),
> 
> > +			 oldsessionid, sessionid, !rc);
> 
> 	tty_kref_put(tty);
> 
> Regards,
> Peter Hurley
> 
> 
> >  	audit_log_end(ab);
> >  }
> >  
> > 
> 

- RGB

--
Richard Guy Briggs <rgb@...hat.com>
Kernel Security Engineering, Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635