Commit 26d5badb authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

signal: Implement force_fatal_sig 

Add a simple helper force_fatal_sig that causes a signal to be
delivered to a process as if the signal handler was set to SIG_DFL.

Reimplement force_sigsegv based upon this new helper.  This fixes
force_sigsegv so that when it forces the default signal handler
to be used the code now forces the signal to be unblocked as well.

Reusing the tested logic in force_sig_info_to_task that was built for
force_sig_seccomp this makes the implementation trivial.

This is interesting both because it makes force_sigsegv simpler and
because there are a couple of buggy places in the kernel that call
do_exit(SIGILL) or do_exit(SIGSYS) because there is no straight
forward way today for those places to simply force the exit of a
process with the chosen signal.  Creating force_fatal_sig allows
those places to be implemented with normal signal exits.

Link: https://lkml.kernel.org/r/20211020174406.17889-13-ebiederm@xmission.com


Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
parent 111e7049

include/linux/sched/signal.h

+1 −0
Original line number Diff line number Diff line
@@ -338,6 +338,7 @@ extern int kill_pid(struct pid *pid, int sig, int priv); 
extern __must_check bool do_notify_parent(struct task_struct *, int);

extern void __wake_up_parent(struct task_struct *p, struct task_struct *parent);

extern void force_sig(int);

extern void force_fatal_sig(int);

extern int send_sig(int, struct task_struct *, int);

extern int zap_other_threads(struct task_struct *p);

extern struct sigqueue *sigqueue_alloc(void);

kernel/signal.c

+17 −9
Original line number Diff line number Diff line
@@ -1662,6 +1662,19 @@ void force_sig(int sig) 
}

EXPORT_SYMBOL(force_sig);



void force_fatal_sig(int sig)

{

	struct kernel_siginfo info;



	clear_siginfo(&info);

	info.si_signo = sig;

	info.si_errno = 0;

	info.si_code = SI_KERNEL;

	info.si_pid = 0;

	info.si_uid = 0;

	force_sig_info_to_task(&info, current, true);

}



/*

 * When things go south during signal handling, we

 * will force a SIGSEGV. And if the signal that caused
@@ -1670,14 +1683,9 @@ EXPORT_SYMBOL(force_sig); 
 */

void force_sigsegv(int sig)

{

	struct task_struct *p = current;



	if (sig == SIGSEGV) {

		unsigned long flags;

		spin_lock_irqsave(&p->sighand->siglock, flags);

		p->sighand->action[sig - 1].sa.sa_handler = SIG_DFL;

		spin_unlock_irqrestore(&p->sighand->siglock, flags);

	}

	if (sig == SIGSEGV)

		force_fatal_sig(SIGSEGV);

	else

		force_sig(SIGSEGV);

}