[PATCH 13/20] signal: Implement force_fatal_sig

Eric W. Biederman
2021-10-20T17:45:42Z

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.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
include/linux/sched/signal.h | 1 +
kernel/signal.c | 26 +++++++++++++++++---------
2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index e5f4ce622ee6..e2dc9f119ada 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -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);
diff --git a/kernel/signal.c b/kernel/signal.c
index 952741f6d0f9..6a5e1802b9a2 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -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
@@ -1670,15 +1683,10 @@ 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);
- }
- force_sig(SIGSEGV);
+ if (sig == SIGSEGV)
+ force_fatal_sig(SIGSEGV);
+ else
+ force_sig(SIGSEGV);
}

int force_sig_fault_to_task(int sig, int code, void __user *addr
--
2.20.1