call_usermodehelper signals bug ?

From: Stelian Pop (stelian.pop@fr.alcove.com)
Date: Fri Feb 21 2003 - 10:22:27 EST

Hi,

I think there is a bug involved somewhere in the signal treatment
for a program launched via the new call_usermodehelper, but I
have trouble trying to pinpoint it.

The problem is visible on my RedHat 8.0 scripts, when I insert
a pcmcia network card. This in turn launches hotplug, which launches
/sbin/ifup, which launches /sbin/arping, which never ends (although
he should end upon reception of 3 times SIGALRM, triggered by alarm(1)):
        # strace -p 2588
        recvfrom(0, "\0\1\10\0\6\4\0\1\0P\4\2\304\304QP\365\222\0\0\0\0\0\0"..., 4096, 0, {sin_family=AF_PACKET, proto=0x806, if3, pkttype=1, addr(6)={1, }, [20]) = 46
        rt_sigprocmask(SIG_BLOCK, [INT ALRM], ~[KILL CHLD STOP], 8) = 0
        gettimeofday({1045840191, 536542}, NULL) = 0
        rt_sigprocmask(SIG_SETMASK, ~[KILL CHLD STOP], NULL, 8) = 0
        recvfrom(0, "\0\1\10\0\6\4\0\1\0P\4\2\304\304QP\365\222\0\0\0\0\0\0"..., 4096, 0, {sin_family=AF_PACKET, proto=0x806, if3, pkttype=1, addr(6)={1, }, [20]) = 46
        rt_sigprocmask(SIG_BLOCK, [INT ALRM], ~[KILL CHLD STOP], 8) = 0
        gettimeofday({1045840192, 528618}, NULL) = 0
        rt_sigprocmask(SIG_SETMASK, ~[KILL CHLD STOP], NULL, 8) = 0

As a result, the network doesn't come up at all.

I succeded in reproducing the bug with a simple module which calls
call_usermodehelper and a foo.c program which uses SIGALRM (derived
from arping source code).

I feel that this has something to do with the elimination of
        sigemptyset(&curtask->blocked);
        flush_signals(curtask);
        flush_signal_handlers(curtask);
        recalc_sigpending(curtask);
in call_usermodehelper() with the new implementation but I'm not
expert in this area.

Here is the simple module:
        #include <linux/module.h>
        #include <linux/init.h>
        #include <linux/kernel.h>
        #include <linux/kmod.h>

        static int test_init(void) {
                char *argv[2], *envp[1];
                argv[0] = "/tmp/foo";
                argv[1] = 0;
                envp[0] = 0;
                return call_usermodehelper(argv [0], argv, envp, 0);
        }
        
        module_init(test_init);

And the usermode program:
        #include <sys/signal.h>
        #include <unistd.h>
        #include <stdio.h>

        void set_signal(int signo, void (*handler)(void))
        {
                struct sigaction sa;
        
                memset(&sa, 0, sizeof(sa));
                sa.sa_handler = (void (*)(int))handler;
                sa.sa_flags = SA_RESTART;
                sigaction(signo, &sa, NULL);
        }
        
        void catcher(void)
        {
                static int count = 0;
                printf("Here\n");
                if (++count == 3)
                        exit(0);
                alarm(1);
        }
        
        int
        main(int argc, char **argv)
        {
                set_signal(SIGALRM, catcher);
        
                catcher();
        
                while(1) {
                        sleep(1);
                }
        }

Does this ring a bell to someone ?

Thanks,

Stelian. 

-- 
Stelian Pop <stelian.pop@fr.alcove.com>
Alcove - http://www.alcove.com
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