> and I forgot to mention, if you want to add PIDFD_SIGNAL_PRGP you can > look at __kill_pgrp_info(). Yeah, I did that and there's a semantical twist in the old kill(2) system call that made me think: (1) kill(-1234) => kill process group with id 1234 (2) kill(0) => kill process group of @current which implementation wise is indicated by __kill_pgrp_info(..., pid ? find_vpid(-pid) ? task_pgrp(current)) We're obviously not going to implement (2) as that doesn't really make a sense for pidfd_send_signal(). But (1) is also wrong for pidfd_send_signal(). If we'd ever implement (1) it should be via pidfd_open(1234, PIDFD_PROCESS_GROUP). So if PIDFD_PROCESS_GROUP is set then we want to send a signal to the process group that @pidfd is in. Unless there's reasons we can't do this. I tried to draft this and what I have is a totally uncompiled draft. I was unsure how best to cleanly express how to take the process group from the struct pid of that @pidfd. So I modeled it after how we do it for PIDTYPE_TGID. >From 8d886b07cc1b17cc6dd3a9ebf19c51212282b6f5 Mon Sep 17 00:00:00 2001 From: Christian Brauner <brauner@xxxxxxxxxx> Date: Fri, 9 Feb 2024 15:49:45 +0100 Subject: [PATCH] [RFC] 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 There's a semantical quirk in the old kill(2) system call that made me think: (1) kill(-1234) => kill process group with id 1234 (2) kill(0) => kill process group of @current as indicated by __kill_pgrp_info(..., pid ? find_vpid(-pid) ? task_pgrp(current)) We're obviously not going to implement (2) as that doesn't really make a lot of sense for pidfd_send_signal(). But (1) is also wrong for pidfd_send_signal(). If we'd ever implement (1) it should be via pidfd_open(..., PIDFD_PROCESS_GROUP). Link: https://github.com/systemd/systemd/issues/31093 [1] Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx> --- include/uapi/linux/pidfd.h | 5 +++++ kernel/signal.c | 46 ++++++++++++++++++++++++++++++++++---- 2 files changed, 47 insertions(+), 4 deletions(-) diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h index 2e6461459877..72ec000a97cd 100644 --- a/include/uapi/linux/pidfd.h +++ b/include/uapi/linux/pidfd.h @@ -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 */ diff --git a/kernel/signal.c b/kernel/signal.c index 8b8169623850..f0f9a5a822b4 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3873,6 +3873,23 @@ static struct pid *pidfd_to_pid(const struct file *file) return tgid_pidfd_to_pid(file); } +static int kill_pgrp_info(int sig, struct kernel_siginfo *info, struct pid *pid) +{ + struct task_struct *p; + int ret = -ESRCH; + + read_lock(&tasklist_lock); + p = pid_task(pid, PIDTYPE_PID); + if (p) + ret = __kill_pgrp_info(sig, info, task_pgrp(p)); + read_unlock(&tasklist_lock); + return ret; +} + +#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 +3914,11 @@ 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 +3936,24 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, if (!access_pidfd_pidns(pid)) goto err; - if (f.file->f_flags & PIDFD_THREAD) + 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; - else + 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); @@ -3938,7 +3973,10 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, prepare_kill_siginfo(sig, &kinfo, type); } - ret = kill_pid_info_type(sig, &kinfo, pid, type); + if (type == PIDFD_SIGNAL_PROCESS_GROUP) + ret = kill_pgrp_info(sig, &kinfo, pid); + else + ret = kill_pid_info_type(sig, &kinfo, pid, type); err: fdput(f); return ret; -- 2.43.0
