Package: schroot
Version: 1.3.1-1
Severity: minor
User: ubuntu-de...@lists.ubuntu.com
Usertags: origin-ubuntu lucid
Hi!
I seem to have run into a weird glitch when using the "command-prefix"
option of schroot. Namely, schroot is backgrounded by my shell on exit
because it receives SIGTTOU when attempting to reset the termios on
CTTY_FILENO:
$ schroot -u root -c lucid
cloning (with CLONE_NEWPID) for child
parent waiting
running child
(lucid)r...@system:/tmp# exit
parent done, exiting 0
[1]+ Stopped schroot -u root -c lucid
$ echo $?
150
$ fg
schroot -u root -c lucid
$ echo $?
0
This happens for me because I've been playing with the CLONE_NEW* flags,
and it seems that CLONE_NEWPID seems to trigger the tty layer into sending
SIGTTOU when it attempts to reset the termios.
I can, for some reason, trigger this without anything very heavy-weight by
calling "bash -i" from a simple wrapper, but that just illustrates the
problem -- I'm not sure why it's happening under schroot only with
CLONE_NEWPID.
Attached is
- "minimal.c" shows the signal arriving in a simple environment.
- "runalt.c" which I use with command-prefix like this:
# works:
#command-prefix=/scratch/src/newpid/altrun,fork
#command-prefix=/scratch/src/newpid/altrun,clone
command-prefix=/scratch/src/newpid/altrun,clone-newnet
# breaks:
#command-prefix=/scratch/src/newpid/altrun,clone-newpid
I'm at a loss. "minimal.c" behaves the same on older kernels, so I'm
assuming this isn't a kernel bug. Maybe bash is doing something weird
when it finds itself running as PID 1?
Thanks,
-Kees
--
Kees Cook @debian.org
// Copyright (C) 2010, Kees Cook <k...@ubuntu.com>
// License: GPLv3
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <termios.h>
#include <unistd.h>
#include <stdint.h>
#include <string.h>
#include <signal.h>
#include <stdint.h>
#include <stddef.h>
#include <inttypes.h>
void catch_ttou(int sig) {
printf("Caught SIGTTOU!\n");
/* need to ignore or we will catch this until our parent backgrounds us */
signal(SIGTTOU,SIG_IGN);
}
int main(int argc, char * argv[])
{
struct termios saved_termios;
struct termios after_termios;
signal(SIGTTOU,catch_ttou);
if (tcgetattr(STDIN_FILENO, &saved_termios) < 0) {
perror("tcgetattr");
return -1;
}
printf("spawning termios fiddler...\n");
system("/bin/bash -i -c /bin/true");
printf("reset termios ...\n");
if (tcsetattr(STDIN_FILENO, TCSANOW, &saved_termios) < 0) {
perror("tcsetattr");
return -1;
}
return 0;
}
// Copyright (C) 2010, Kees Cook <k...@ubuntu.com>
// License: GPLv3
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>
#include <string.h>
#include <stdint.h>
#include <stddef.h>
#include <inttypes.h>
#include <sched.h>
#include <signal.h>
int child(void *ptr)
{
char **argv = ptr;
printf("running child\n");
execv(*argv,argv);
perror("execv");
return -1;
}
int main(int argc, char * argv[])
{
int status;
uint8_t stack[4096];
int flags = SIGCHLD;
if (argc<3) {
fprintf(stderr,"Usage: %s [fork|clone|clone-newpid|clone-newnet] cmd arg arg...\n", argv[0]);
return -1;
}
if (strcmp(argv[1],"clone-newpid")==0) {
flags |= CLONE_NEWPID;
}
if (strcmp(argv[1],"clone-newnet")==0) {
flags |= CLONE_NEWNET;
}
if (strcmp(argv[1],"fork")==0) {
printf("forking for child\n");
switch (fork()) {
case -1:
perror("fork");
return -1;
case 0:
exit(child(argv+2));
default:
break;
}
}
else {
printf("cloning %sfor child\n",
((flags & CLONE_NEWPID) == CLONE_NEWPID) ? "(with CLONE_NEWPID) " :
( ((flags & CLONE_NEWNET) == CLONE_NEWNET) ? "(with CLONE_NEWNET) " : ""));
if (clone(child, stack+sizeof(stack), flags, argv+2)<0) {
perror("clone");
return -1;
}
}
printf("parent waiting\n");
waitpid(-1, &status, __WALL);
printf("parent done, exiting %d\n", WEXITSTATUS(status));
return WEXITSTATUS(status);
}
