Date: Sat, 21 Aug 1999 17:40:47 +0100 (BST) From: dwmalone@maths.tcd.ie To: FreeBSD-gnats-submit@freebsd.org Cc: cracauer@freebsd.org, bde@freebsd.org Subject: kern/13293: You can catch SIGKILL and SIGSTOP in 4.0. Message-ID: <199908211740.aa28643@walton.maths.tcd.ie>
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>Number: 13293
>Category: kern
>Synopsis: You can catch SIGKILL and SIGSTOP in 4.0.
>Confidential: no
>Severity: serious
>Priority: high
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Sat Aug 21 09:50:00 PDT 1999
>Closed-Date:
>Last-Modified:
>Originator: David Malone
>Release: FreeBSD 4.0-CURRENT i386
>Organization:
School of Mathematics, Trinity College, Dublin.
>Environment:
Any 4.0 machine with a version of kern_sig.c later than 1.57.
>Description:
Sigaction is supposed to check if you change the handler of SIGKILL
or SIGSTOP to anything but SIG_DFL. In revision 1.57 one instance
too many of sa->sa_handler got replaced by ps->ps_sigact[signum].
Resultingly it checks if the current handler is SIG_DFL instead of
the new handler being SIG_DFL. This means you can create un-killable
un-stoppable processes.
>How-To-Repeat:
The following program is unkillable.
#include <stdio.h>
#include <sys/types.h>
#include <signal.h>
void sighand(int sig)
{
printf("Caught signal %d\n",sig);
}
int main(int argc,char **argv)
{
int i;
for( i = 0 ; i < 32 ; i++ )
signal(i,sighand);
while(1);
exit(0);
}
>Fix:
--- kern_sig.c 1999/08/16 18:13:38 1.60
+++ kern_sig.c 1999/08/21 16:06:30
@@ -155,11 +155,11 @@
if (uap->nsa) {
if ((error = copyin((caddr_t)uap->nsa, (caddr_t)sa,
sizeof (vec))))
return (error);
if ((signum == SIGKILL || signum == SIGSTOP) &&
- ps->ps_sigact[signum] != SIG_DFL)
+ sa->sa_handler != SIG_DFL)
return (EINVAL);
setsigvec(p, signum, sa);
}
return (0);
}
>Release-Note:
>Audit-Trail:
>Unformatted:
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