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signal: Implement force_fatal_sig

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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: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2021-10-20 12:43:59 -05:00
parent 111e70490d
commit 26d5badbcc
2 changed files with 18 additions and 9 deletions
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1
include/linux/sched/signal.h
View File

@ -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);

26
kernel/signal.c
View File

@ -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