user/sven/linux.git/samples/pidfd, branch v5.5

samples: make pidfd-metadata fail gracefully on older kernels

2019-06-24T13:55:50Z

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 Signed-off-by: Christian Brauner

samples: fix pidfd-metadata compilation

2019-06-05T13:06:07Z

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 Reported-by: Guenter Roeck Cc: Christian Brauner Signed-off-by: Guenter Roeck [christian@brauner.io: tweak commit message] Signed-off-by: Christian Brauner

samples: add .gitignore for pidfd-metadata

2019-05-10T09:50:52Z

Ignore the pidfd-metadata binary so it doesn't show up in unwanted scenarios. Reported-by: Linus Torvalds Signed-off-by: Christian Brauner

samples: show race-free pidfd metadata access

2019-05-07T12:31:04Z

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 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 Co-developed-by: Jann Horn Signed-off-by: Jann Horn Reviewed-by: Oleg Nesterov Cc: Arnd Bergmann Cc: "Eric W. Biederman" Cc: Kees Cook Cc: Thomas Gleixner Cc: David Howells Cc: "Michael Kerrisk (man-pages)" Cc: Andy Lutomirsky Cc: Andrew Morton Cc: Aleksa Sarai Cc: Linus Torvalds Cc: Al Viro