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43c6afee48
This is a sample program showing userspace how to get race-free access
to process metadata from a pidfd. It is rather easy to do and userspace
can actually simply reuse code that currently parses a process's status
file in procfs.
The program can easily be extended into a generic helper suitable for
inclusion in a libc to make it even easier for userspace to gain metadata
access.
Since this came up in a discussion because this API is going to be used
in various service managers: A lot of programs will have a whitelist
seccomp filter that returns <some-errno> for all new syscalls. This
means that programs might get confused if CLONE_PIDFD works but the
later pidfd_send_signal() syscall doesn't. Hence, here's a ahead of
time check that pidfd_send_signal() is supported:
bool pidfd_send_signal_supported()
{
int procfd = open("/proc/self", O_DIRECTORY | O_RDONLY | O_CLOEXEC);
if (procfd < 0)
return false;
/*
* A process is always allowed to signal itself so
* pidfd_send_signal() should never fail this test. If it does
* it must mean it is not available, blocked by an LSM, seccomp,
* or other.
*/
return pidfd_send_signal(procfd, 0, NULL, 0) == 0;
}
Signed-off-by: Christian Brauner <christian@brauner.io>
Co-developed-by: Jann Horn <jannh@google.com>
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Howells <dhowells@redhat.com>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
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| .. | ||
| auxdisplay | ||
| binderfs | ||
| bpf | ||
| configfs | ||
| connector | ||
| hidraw | ||
| hw_breakpoint | ||
| kdb | ||
| kfifo | ||
| kobject | ||
| kprobes | ||
| livepatch | ||
| mei | ||
| mic/mpssd | ||
| pidfd | ||
| pktgen | ||
| qmi | ||
| rpmsg | ||
| seccomp | ||
| statx | ||
| timers | ||
| trace_events | ||
| trace_printk | ||
| uhid | ||
| v4l | ||
| vfio-mdev | ||
| watchdog | ||
| Kconfig | ||
| Makefile | ||