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pidfd: allow to override signal scope in pidfd_send_signal()

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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: Oleg 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: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2024-02-09 15:49:45 +01:00
parent 81b9d8ac06
commit e1fb1dc08e
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GPG Key ID: 91C61BC06578DCA2
2 changed files with 42 additions and 9 deletions
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5
include/uapi/linux/pidfd.h
View File

@ -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 */

46
kernel/signal.c
View File

@ -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;
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);
@ -3931,14 +3956,17 @@ 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);
}
ret = kill_pid_info_type(sig, &kinfo, pid, 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);
return ret;