This patchset introduces a mechanism (pidfd_getfd syscall) to get file descriptors from other processes via pidfd. Although this can be achieved using SCM_RIGHTS, and parasitic code injection, this offers a more straightforward mechanism, with less overhead and complexity. The process under manipulation's fd still remains. It includes a model for extensibility, specifically to allow for future features around cgroup migration of sockets, and allowing for the fd to be taken (closing the fd in the process under manipulation). The syscall numbers were chosen to be one greater than openat2. Summary of history: This initially started as a ptrace command. It did not require the process to be stopped, and felt like kind of an awkward fit for ptrace. After that, it moved to an ioctl on the pidfd. Given functionality, it made sense to make it a syscall which did not require the process to be stopped. Changes since v4: * Turn into a syscall * Move to PTRACE_MODE_ATTACH_REALCREDS from PTRACE_MODE_READ_REALCREDS * Remove the sample code. This will come in another patchset, as the new self-tests cover all the functionality. Changes since v3: * Add self-test * Move to ioctl passing fd directly, versus args struct * Shuffle around include files Changes since v2: * Move to ioctl on pidfd instead of ptrace function * Add security check before moving file descriptor Changes since the RFC v1: * Introduce a new helper to fs/file.c to fetch a file descriptor from any process. It largely uses the code suggested by Oleg, with a few changes to fix locking * It uses an extensible options struct to supply the FD, and option. * I added a sample, using the code from the user-ptrace sample Sargun Dhillon (3): vfs, fdtable: Add get_task_file helper pid: Introduce pidfd_getfd syscall test: Add test for pidfd getfd MAINTAINERS | 1 + arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 2 + arch/ia64/kernel/syscalls/syscall.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + fs/file.c | 22 +- include/linux/file.h | 2 + include/linux/syscalls.h | 4 + include/uapi/asm-generic/unistd.h | 3 +- include/uapi/linux/pidfd.h | 10 + kernel/pid.c | 115 ++++++++ tools/testing/selftests/pidfd/.gitignore | 1 + tools/testing/selftests/pidfd/Makefile | 2 +- .../selftests/pidfd/pidfd_getfd_test.c | 262 ++++++++++++++++++ 28 files changed, 437 insertions(+), 5 deletions(-) create mode 100644 include/uapi/linux/pidfd.h create mode 100644 tools/testing/selftests/pidfd/pidfd_getfd_test.c -- 2.20.1
