From fae5fa44f1fd079ffbed8e0add929dd7bbd1347f Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 30 Apr 2008 00:53:03 -0700 Subject: signals: fix /sbin/init protection from unwanted signals The global init has a lot of long standing problems with the unhandled fatal signals. - The "is_global_init(current)" check in get_signal_to_deliver() protects only the main thread. Sub-thread can dequee the fatal signal and shutdown the whole thread group except the main thread. If it dequeues SIGSTOP /sbin/init will be stopped, this is not right too. Note that we can't use is_global_init(->group_leader), this breaks exec and this can't solve other problems we have. - Even if afterwards ignored, the fatal signals sets SIGNAL_GROUP_EXIT on delivery. This breaks exec, has other bad implications, and this is just wrong. Introduce the new SIGNAL_UNKILLABLE flag to fix these problems. It also helps to solve some other problems addressed by the subsequent patches. Currently we use this flag for the global init only, but it could also be used by kthreads and (perhaps) by the sub-namespace inits. Signed-off-by: Oleg Nesterov Acked-by: "Eric W. Biederman" Cc: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/sched.h | 2 ++ init/main.c | 2 ++ kernel/signal.c | 9 ++++++--- 3 files changed, 10 insertions(+), 3 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 0917b3df12d5..fe970cdca83c 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -561,6 +561,8 @@ struct signal_struct { #define SIGNAL_CLD_CONTINUED 0x00000020 #define SIGNAL_CLD_MASK (SIGNAL_CLD_STOPPED|SIGNAL_CLD_CONTINUED) +#define SIGNAL_UNKILLABLE 0x00000040 /* for init: ignore fatal signals */ + /* If true, all threads except ->group_exit_task have pending SIGKILL */ static inline int signal_group_exit(const struct signal_struct *sig) { diff --git a/init/main.c b/init/main.c index 624266b524d4..1f4406477f83 100644 --- a/init/main.c +++ b/init/main.c @@ -802,6 +802,8 @@ static int noinline init_post(void) (void) sys_dup(0); (void) sys_dup(0); + current->signal->flags |= SIGNAL_UNKILLABLE; + if (ramdisk_execute_command) { run_init_process(ramdisk_execute_command); printk(KERN_WARNING "Failed to execute %s\n", diff --git a/kernel/signal.c b/kernel/signal.c index 02ef3548aeb0..646a8765696a 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -728,7 +728,8 @@ static void complete_signal(int sig, struct task_struct *p, int group) * Found a killable thread. If the signal will be fatal, * then start taking the whole group down immediately. */ - if (sig_fatal(p, sig) && !(signal->flags & SIGNAL_GROUP_EXIT) && + if (sig_fatal(p, sig) && + !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) && !sigismember(&t->real_blocked, sig) && (sig == SIGKILL || !(t->ptrace & PT_PTRACED))) { /* @@ -1615,7 +1616,8 @@ static int do_signal_stop(int signr) } else { struct task_struct *t; - if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED) || + if (unlikely((sig->flags & (SIGNAL_STOP_DEQUEUED | SIGNAL_UNKILLABLE)) + != SIGNAL_STOP_DEQUEUED) || unlikely(signal_group_exit(sig))) return 0; /* @@ -1761,7 +1763,8 @@ relock: /* * Global init gets no signals it doesn't want. */ - if (is_global_init(current)) + if (unlikely(signal->flags & SIGNAL_UNKILLABLE) && + !signal_group_exit(signal)) continue; if (sig_kernel_stop(signr)) { -- cgit v1.2.2