[PATCH v1 0/2] proc: allow signaling processes via file descriptors

Christian Brauner
2018-11-19T10:33:35Z

Hey,

This little series introduces the ability to signal processes via file
descriptors to eliminate race-conditions caused by pid recycling.
With this patch an open() call on /proc/<pid> will give userspace a
handle to struct pid of the process associated with /proc/<pid>. This
allows to maintain a stable handle on a process.
Discussion has shown that a dedicated syscall is prefered over an ioctl().
Thus, the new syscall procfd_signal() is introduced to solve this
problem. It operates on a process file descriptor. More details are
found in the individual commit messages.

With this series a process can be killed via:

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
int ret;
char buf[1000];

if (argc < 2)
exit(EXIT_FAILURE);

ret = snprintf(buf, sizeof(buf), "/proc/%s", argv[1]);
if (ret < 0)
exit(EXIT_FAILURE);

int fd = open(buf, O_DIRECTORY | O_CLOEXEC);
if (fd < 0) {
printf("%s - Failed to open \"%s\"\n", strerror(errno), buf);
exit(EXIT_FAILURE);
}

ret = syscall(__NR_procfd_signal, fd, SIGKILL, NULL, 0);
if (ret < 0) {
printf("Failed to send SIGKILL \"%s\"\n", strerror(errno));
close(fd);
exit(EXIT_FAILURE);
}

close(fd);

exit(EXIT_SUCCESS);
}

Thanks!
Christian

Christian Brauner (2):
proc: get process file descriptor from /proc/<pid>
signal: add procfd_signal() syscall
procfd_signal.2: document procfd_signal syscall

arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
fs/proc/base.c | 23 ++++++++
include/linux/proc_fs.h | 1 +
include/linux/syscalls.h | 2 +
kernel/signal.c | 76 ++++++++++++++++++++++++--
6 files changed, 98 insertions(+), 6 deletions(-)

--
2.19.1