Unverified Commit e1fb1dc0 authored by Christian Brauner's avatar Christian Brauner
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pidfd: allow to override signal scope in pidfd_send_signal() 



Right now we determine the scope of the signal based on the type of
pidfd. There are use-cases where it's useful to override the scope of
the signal. For example in [1]. Add flags to determine the scope of the
signal:

(1) PIDFD_SIGNAL_THREAD: send signal to specific thread reference by @pidfd
(2) PIDFD_SIGNAL_THREAD_GROUP: send signal to thread-group of @pidfd
(2) PIDFD_SIGNAL_PROCESS_GROUP: send signal to process-group of @pidfd

Since we now allow specifying PIDFD_SEND_PROCESS_GROUP for
pidfd_send_signal() to send signals to process groups we need to adjust
the check restricting si_code emulation by userspace to account for
PIDTYPE_PGID.

Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Link: https://github.com/systemd/systemd/issues/31093 [1]
Link: https://lore.kernel.org/r/20240210-chihuahua-hinzog-3945b6abd44a@brauner
Link: https://lore.kernel.org/r/20240214123655.GB16265@redhat.com


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 81b9d8ac

include/uapi/linux/pidfd.h

+5 −0
Original line number Diff line number Diff line
@@ -10,4 +10,9 @@ 
#define PIDFD_NONBLOCK	O_NONBLOCK

#define PIDFD_THREAD	O_EXCL



/* Flags for pidfd_send_signal(). */

#define PIDFD_SIGNAL_THREAD		(1UL << 0)

#define PIDFD_SIGNAL_THREAD_GROUP	(1UL << 1)

#define PIDFD_SIGNAL_PROCESS_GROUP	(1UL << 2)



#endif /* _UAPI_LINUX_PIDFD_H */

kernel/signal.c

+37 −9
Original line number Diff line number Diff line
@@ -1905,16 +1905,19 @@ int send_sig_fault_trapno(int sig, int code, void __user *addr, int trapno, 
	return send_sig_info(info.si_signo, &info, t);

}



int kill_pgrp(struct pid *pid, int sig, int priv)

static int kill_pgrp_info(int sig, struct kernel_siginfo *info, struct pid *pgrp)

{

	int ret;



	read_lock(&tasklist_lock);

	ret = __kill_pgrp_info(sig, __si_special(priv), pid);

	ret = __kill_pgrp_info(sig, info, pgrp);

	read_unlock(&tasklist_lock);



	return ret;

}



int kill_pgrp(struct pid *pid, int sig, int priv)

{

	return kill_pgrp_info(sig, __si_special(priv), pid);

}

EXPORT_SYMBOL(kill_pgrp);



int kill_pid(struct pid *pid, int sig, int priv)
@@ -3873,6 +3876,10 @@ static struct pid *pidfd_to_pid(const struct file *file) 
	return tgid_pidfd_to_pid(file);

}



#define PIDFD_SEND_SIGNAL_FLAGS                            \

	(PIDFD_SIGNAL_THREAD | PIDFD_SIGNAL_THREAD_GROUP | \

	 PIDFD_SIGNAL_PROCESS_GROUP)



/**

 * sys_pidfd_send_signal - Signal a process through a pidfd

 * @pidfd:  file descriptor of the process
@@ -3897,7 +3904,11 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, 
	enum pid_type type;



	/* Enforce flags be set to 0 until we add an extension. */

	if (flags)

	if (flags & ~PIDFD_SEND_SIGNAL_FLAGS)

		return -EINVAL;



	/* Ensure that only a single signal scope determining flag is set. */

	if (hweight32(flags & PIDFD_SEND_SIGNAL_FLAGS) > 1)

		return -EINVAL;



	f = fdget(pidfd);
@@ -3915,10 +3926,24 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, 
	if (!access_pidfd_pidns(pid))

		goto err;



	switch (flags) {

	case 0:

		/* Infer scope from the type of pidfd. */

		if (f.file->f_flags & PIDFD_THREAD)

			type = PIDTYPE_PID;

		else

			type = PIDTYPE_TGID;

		break;

	case PIDFD_SIGNAL_THREAD:

		type = PIDTYPE_PID;

		break;

	case PIDFD_SIGNAL_THREAD_GROUP:

		type = PIDTYPE_TGID;

		break;

	case PIDFD_SIGNAL_PROCESS_GROUP:

		type = PIDTYPE_PGID;

		break;

	}



	if (info) {

		ret = copy_siginfo_from_user_any(&kinfo, info);
@@ -3931,13 +3956,16 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, 


		/* Only allow sending arbitrary signals to yourself. */

		ret = -EPERM;

		if ((task_pid(current) != pid) &&

		if ((task_pid(current) != pid || type > PIDTYPE_TGID) &&

		    (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))

			goto err;

	} else {

		prepare_kill_siginfo(sig, &kinfo, type);

	}



	if (type == PIDTYPE_PGID)

		ret = kill_pgrp_info(sig, &kinfo, pid);

	else

		ret = kill_pid_info_type(sig, &kinfo, pid, type);

err:

	fdput(f);