Re: Format specifier issue when building kernel

[Richard Guy Briggs <rgb@redhat.com>]

On Fri, Nov 01, 2013 at 12:34:55PM -0400, Steve Grubb wrote:
> On Friday, November 01, 2013 12:24:55 PM Richard Guy Briggs wrote:
> > On Thu, Oct 31, 2013 at 12:25:55PM -0700, William Roberts wrote:
> > > > +                       if (msg_type != AUDIT_USER_TTY) {
> > > > +                               char fmt[64];
> > > > +                               strcat(fmt, " msg='%.");
> > > > +                               strcat(fmt, "AUDIT_MESSAGE_TEXT_MAX");
> > > > +                               strcat(fmt, "s'");
> > > > +                               audit_log_format(ab, fmt, (char *)data);
> > > > +                       } else {
> > > 
> > > I am ok with this. In fact I was going to do this the first time, but I
> > > thought their would be some explicit reason to avoid the additional
> > > run time overhead as the concat could be made at compile time.
> > 
> > Ok, this was in danger of starting with fmt in an unknown state.  Latest
> > patch:
> > 
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > @@ -148,6 +148,8 @@ DEFINE_MUTEX(audit_cmd_mutex);
> >   * should be at least that large. */
> >  #define AUDIT_BUFSIZ 1024
> > 
> > +char usermsg_format[64] = "";
> 
> You might want this ^^^  to be static so its not global in scope.

Yup, good point.  Thanks.

> -Steve
> 
> >  /* AUDIT_MAXFREE is the number of empty audit_buffers we keep on the
> >   * audit_freelist.  Doing so eliminates many kmalloc/kfree calls. */
> >  #define AUDIT_MAXFREE  (2*NR_CPUS)
> > @@ -714,11 +716,15 @@ static int audit_receive_msg(struct sk_buff *skb,
> > struct nlmsghdr *nlh) break;
> >  			}
> >  			audit_log_common_recv_msg(&ab, msg_type);
> > -			if (msg_type != AUDIT_USER_TTY)
> > -				audit_log_format(ab,
> > -						 " msg='%.AUDIT_MESSAGE_TEXT_MAXs'",
> > +			if (msg_type != AUDIT_USER_TTY) {
> > +				if (unlikely(usermsg_format[0] == 0))
> > +					snprintf(usermsg_format,
> > +						sizeof(usermsg_format),
> > +						" msg=\'%%.%ds\'",
> > +						AUDIT_MESSAGE_TEXT_MAX);
> > +				audit_log_format(ab, usermsg_format,
> >  						 (char *)data);
> > -			else {
> > +			} else {
> >  				int size;
> > 
> >  				audit_log_format(ab, " data=");
> > 
> > - RGB
> > 
> > --
> > Richard Guy Briggs <rbriggs@redhat.com>
> > Senior Software Engineer
> > Kernel Security
> > AMER ENG Base Operating Systems
> > Remote, Ottawa, Canada
> > Voice: +1.647.777.2635
> > Internal: (81) 32635
> > Alt: +1.613.693.0684x3545
> > 
> > --
> > Linux-audit mailing list
> > Linux-audit@redhat.com
> > https://www.redhat.com/mailman/listinfo/linux-audit
> 

- RGB

--
Richard Guy Briggs <rbriggs@redhat.com>
Senior Software Engineer
Kernel Security
AMER ENG Base Operating Systems
Remote, Ottawa, Canada
Voice: +1.647.777.2635
Internal: (81) 32635
Alt: +1.613.693.0684x3545