devpts_get_tty() assumes that the inode passed in is associated with a valid
pty. But if the only reference to the pty is via a bind-mount, the inode
passed to devpts_get_tty() while valid, would refer to a pty that no longer
exists.
With a lot of debug effort, Grzegorz Nosek developed a small program (see
below) to reproduce a crash on recent kernels. This crash is a regression
introduced by the commit:
commit 527b3e4773
Author: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Date: Mon Oct 13 10:43:08 2008 +0100
To fix, ensure that the dentry associated with the inode has not yet been
deleted/unhashed by devpts_pty_kill().
See also:
https://lists.linux-foundation.org/pipermail/containers/2009-July/019273.html
tty-bug.c:
#define _GNU_SOURCE
#include <fcntl.h>
#include <sched.h>
#include <stdlib.h>
#include <sys/mount.h>
#include <sys/signal.h>
#include <unistd.h>
#include <stdio.h>
#include <linux/fs.h>
void dummy(int sig)
{
}
static int child(void *unused)
{
int fd;
signal(SIGINT, dummy); signal(SIGHUP, dummy);
pause(); /* cheesy synchronisation to wait for /dev/pts/0 to appear */
mount("/dev/pts/0", "/dev/console", NULL, MS_BIND, NULL);
sleep(2);
fd = open("/dev/console", O_RDWR);
dup(0); dup(0);
write(1, "Hello world!\n", sizeof("Hello world!\n")-1);
return 0;
}
int main(void)
{
pid_t pid;
char *stack;
stack = malloc(16384);
pid = clone(child, stack+16384, CLONE_NEWNS|SIGCHLD, NULL);
open("/dev/ptmx", O_RDWR|O_NOCTTY|O_NONBLOCK);
unlockpt(fd); grantpt(fd);
sleep(2);
kill(pid, SIGHUP);
sleep(1);
return 0; /* exit before child opens /dev/console */
}
Reported-by: Grzegorz Nosek <root@localdomain.pl>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Tested-by: Serge Hallyn <serue@us.ibm.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
edfacdd6f8