On Fri, Feb 09, 2024 at 02:06:50PM +0100, Oleg Nesterov wrote: > Turn kill_pid_info() into kill_pid_info_type(), this allows to pass any > pid_type to group_send_sig_info(), despite its name it should work fine > even if type = PIDTYPE_PID. > > Change pidfd_send_signal() to use PIDTYPE_PID or PIDTYPE_TGID depending > on PIDFD_THREAD. > > While at it kill another TODO comment in pidfd_show_fdinfo(). As Christian > expains fdinfo reports f_flags, userspace can already detect PIDFD_THREAD. > > Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> > --- How do you feel about the following (untested...) addition? I've played with PIDFD_SIGNAL_PROCESS_GROUP as well but that code is fairly new to me so I would need some more time. >From a473512ed8de2e864961f7009e2f20ce4e7a0778 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 (2) PIDFD_SIGNAL_THREAD_GROUP: send signal to thread-group I've put off PIDFD_SIGNAL_PROCESS_GROUP for now since I need to stare at the code a bit longer how this would work. Link: https://github.com/systemd/systemd/issues/31093 [1] Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx> --- include/uapi/linux/pidfd.h | 4 ++++ kernel/signal.c | 35 ++++++++++++++++++++++++++++------- 2 files changed, 32 insertions(+), 7 deletions(-) diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h index 2e6461459877..757ed5a668c6 100644 --- a/include/uapi/linux/pidfd.h +++ b/include/uapi/linux/pidfd.h @@ -10,4 +10,8 @@ #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) + #endif /* _UAPI_LINUX_PIDFD_H */ diff --git a/kernel/signal.c b/kernel/signal.c index 9578ce17d85d..1d6586964099 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3872,6 +3872,9 @@ 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) + /** * sys_pidfd_send_signal - Signal a process through a pidfd * @pidfd: file descriptor of the process @@ -3889,14 +3892,19 @@ static struct pid *pidfd_to_pid(const struct file *file) SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, siginfo_t __user *, info, unsigned int, flags) { - int ret; + int ret, si_code; struct fd f; struct pid *pid; kernel_siginfo_t kinfo; bool thread; + enum pid_type si_scope; /* 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); @@ -3914,7 +3922,22 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, if (!access_pidfd_pidns(pid)) goto err; - thread = f.file->f_flags & PIDFD_THREAD; + switch (flags) { + case 0: + /* Infer scope from the type of pidfd. */ + thread = (f.file->f_flags & PIDFD_THREAD); + si_scope = thread ? PIDTYPE_PID : PIDTYPE_TGID; + si_code = thread ? SI_TKILL : SI_USER; + break; + case PIDFD_SIGNAL_THREAD: + si_scope = PIDTYPE_PID; + si_code = SI_TKILL; + break; + case PIDFD_SIGNAL_THREAD_GROUP: + si_scope = PIDTYPE_TGID; + si_code = SI_USER; + break; + } if (info) { ret = copy_siginfo_from_user_any(&kinfo, info); @@ -3931,12 +3954,10 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL)) goto err; } else { - prepare_kill_siginfo(sig, &kinfo, - thread ? SI_TKILL : SI_USER); + prepare_kill_siginfo(sig, &kinfo, si_code); } - ret = kill_pid_info_type(sig, &kinfo, pid, - thread ? PIDTYPE_PID : PIDTYPE_TGID); + ret = kill_pid_info_type(sig, &kinfo, pid, si_scope); err: fdput(f); return ret; -- 2.43.0
