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From: Christian Brauner <christian@brauner.io>
To: ebiederm@xmission.com, linux-kernel@vger.kernel.org
Cc: serge@hallyn.com, jannh@google.com, luto@kernel.org,
	akpm@linux-foundation.org, oleg@redhat.com, cyphar@cyphar.com,
	viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org, dancol@google.com,
	timmurray@google.com, linux-man@vger.kernel.org,
	Christian Brauner <christian@brauner.io>
Subject: [PATCH v1 0/2] proc: allow signaling processes via file descriptors
Date: Mon, 19 Nov 2018 11:32:37 +0100
Message-ID: <20181119103241.5229-1-christian@brauner.io> (raw)

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


             reply index

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-19 10:32 Christian Brauner [this message]
2018-11-19 10:32 ` [PATCH v1 1/2] proc: get process file descriptor from /proc/<pid> Christian Brauner
2018-11-19 15:32   ` Andy Lutomirski
2018-11-19 18:20     ` Christian Brauner
2018-11-19 10:32 ` [PATCH v1 2/2] signal: add procfd_signal() syscall Christian Brauner
2018-11-19 15:45   ` Andy Lutomirski
2018-11-19 15:57     ` Daniel Colascione
2018-11-19 18:39     ` Christian Brauner
2018-11-19 15:59   ` Daniel Colascione
2018-11-19 18:29     ` Christian Brauner
2018-11-19 19:02       ` Eric W. Biederman
2018-11-19 19:31         ` Christian Brauner
2018-11-19 19:39           ` Daniel Colascione
2018-11-19 17:10   ` Eugene Syromiatnikov
2018-11-19 18:23     ` Christian Brauner
2018-11-19 17:14   ` Eugene Syromiatnikov
2018-11-19 20:28   ` Aleksa Sarai
2018-11-19 20:55     ` Christian Brauner
2018-11-19 21:13       ` Christian Brauner
2018-11-19 21:18       ` Aleksa Sarai
2018-11-19 21:20         ` Christian Brauner
2018-11-19 21:21         ` Christian Brauner
2018-11-19 21:25           ` Aleksa Sarai
2018-11-19 21:26           ` Daniel Colascione
2018-11-19 21:36             ` Aleksa Sarai
2018-11-19 21:37             ` Christian Brauner
2018-11-19 21:41               ` Daniel Colascione
2018-11-20  4:59                 ` Eric W. Biederman
2018-11-20 10:31                   ` Christian Brauner
2018-11-21 21:39                     ` Serge E. Hallyn
2018-11-19 21:23         ` Aleksa Sarai
2018-11-22  7:41           ` Serge E. Hallyn
2018-11-19 22:39   ` Tycho Andersen
2018-11-19 22:49     ` Daniel Colascione
2018-11-19 23:07       ` Tycho Andersen
2018-11-20  0:27         ` Andy Lutomirski
2018-11-20  0:32           ` Christian Brauner
2018-11-20  0:34             ` Andy Lutomirski
2018-11-20  0:49           ` Daniel Colascione
2018-11-22  7:48     ` Serge E. Hallyn
2018-11-19 23:35   ` kbuild test robot
2018-11-19 23:37   ` kbuild test robot
2018-11-19 23:45     ` Christian Brauner
2018-11-28 21:45   ` Joey Pabalinas
2018-11-28 22:05     ` Christian Brauner
2018-11-28 23:02       ` Joey Pabalinas
2018-11-19 10:32 ` [PATCH] procfd_signal.2: document procfd_signal syscall Christian Brauner
2018-11-20 13:29   ` Michael Kerrisk (man-pages)
2018-11-28 20:59   ` Florian Weimer
2018-11-28 21:12     ` Christian Brauner

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