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2019-06-24samples: make pidfd-metadata fail gracefully on older kernelsDmitry V. Levin1-2/+6
Initialize pidfd to an invalid descriptor, to fail gracefully on those kernels that do not implement CLONE_PIDFD and leave pidfd unchanged. Signed-off-by: Dmitry V. Levin <ldv@altlinux.org> Signed-off-by: Christian Brauner <christian@brauner.io>
2019-06-05samples: fix pidfd-metadata compilationGuenter Roeck1-0/+4
Define __NR_pidfd_send_signal if it isn't to prevent a compilation error. To make pidfd-metadata compile on all arches, irrespective of whether or not syscall numbers are assigned, define the syscall number to -1. If it isn't defined this will cause the kernel to return -ENOSYS. Fixes: 43c6afee48d4 ("samples: show race-free pidfd metadata access") Reported-by: Arnd Bergmann <arnd@arndb.de> Reported-by: Guenter Roeck <linux@roeck-us.net> Cc: Christian Brauner <christian@brauner.io> Signed-off-by: Guenter Roeck <linux@roeck-us.net> [christian@brauner.io: tweak commit message] Signed-off-by: Christian Brauner <christian@brauner.io>
2019-05-10samples: add .gitignore for pidfd-metadataChristian Brauner1-0/+1
Ignore the pidfd-metadata binary so it doesn't show up in unwanted scenarios. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Christian Brauner <christian@brauner.io>
2019-05-07samples: show race-free pidfd metadata accessChristian Brauner2-0/+118
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>