Re: [PATCH 01/10] clone: add CLONE_PIDFD

Greg Kroah-Hartman
2021-01-04T13:02:31Z

On Fri, Dec 04, 2020 at 02:31:55AM +0800, Wen Yang wrote:
> From: Christian Brauner <christian@brauner.io>
>
> [ Upstream commit b3e5838252665ee4cfa76b82bdf1198dca81e5be ]
>
> This patchset makes it possible to retrieve pid file descriptors at
> process creation time by introducing the new flag CLONE_PIDFD to the
> clone() system call. Linus originally suggested to implement this as a
> new flag to clone() instead of making it a separate system call. As
> spotted by Linus, there is exactly one bit for clone() left.
>
> CLONE_PIDFD creates file descriptors based on the anonymous inode
> implementation in the kernel that will also be used to implement the new
> mount api. They serve as a simple opaque handle on pids. Logically,
> this makes it possible to interpret a pidfd differently, narrowing or
> widening the scope of various operations (e.g. signal sending). Thus, a
> pidfd cannot just refer to a tgid, but also a tid, or in theory - given
> appropriate flag arguments in relevant syscalls - a process group or
> session. A pidfd does not represent a privilege. This does not imply it
> cannot ever be that way but for now this is not the case.
>
> A pidfd comes with additional information in fdinfo if the kernel supports
> procfs. The fdinfo file contains the pid of the process in the callers
> pid namespace in the same format as the procfs status file, i.e. "Pid:\t%d".
>
> As suggested by Oleg, with CLONE_PIDFD the pidfd is returned in the
> parent_tidptr argument of clone. This has the advantage that we can
> give back the associated pid and the pidfd at the same time.
>
> To remove worries about missing metadata access this patchset comes with
> a sample program that illustrates how a combination of CLONE_PIDFD, and
> pidfd_send_signal() can be used to gain race-free access to process
> metadata through /proc/<pid>. The sample program can easily be
> translated into a helper that would be suitable for inclusion in libc so
> that users don't have to worry about writing it themselves.
>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> 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>
> Cc: <stable@vger.kernel.org> # 4.9.x
> (clone: fix up cherry-pick conflicts for b3e583825266)
> Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
> ---
> include/linux/pid.h | 1 +
> include/uapi/linux/sched.h | 1 +
> kernel/fork.c | 119 +++++++++++++++++++++++++++++++++++++++++++--
> 3 files changed, 117 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index 97b745d..7599a78 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -73,6 +73,7 @@ struct pid_link
> struct hlist_node node;
> struct pid *pid;
> };
> +extern const struct file_operations pidfd_fops;
>
> static inline struct pid *get_pid(struct pid *pid)
> {
> diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
> index 5f0fe01..ed6e31d 100644
> --- a/include/uapi/linux/sched.h
> +++ b/include/uapi/linux/sched.h
> @@ -9,6 +9,7 @@
> #define CLONE_FS 0x00000200 /* set if fs info shared between processes */
> #define CLONE_FILES 0x00000400 /* set if open files shared between processes */
> #define CLONE_SIGHAND 0x00000800 /* set if signal handlers and blocked signals shared */
> +#define CLONE_PIDFD 0x00001000 /* set if a pidfd should be placed in parent */
> #define CLONE_PTRACE 0x00002000 /* set if we want to let tracing continue on the child too */
> #define CLONE_VFORK 0x00004000 /* set if the parent wants the child to wake it up on mm_release */
> #define CLONE_PARENT 0x00008000 /* set if we want to have the same parent as the cloner */
> diff --git a/kernel/fork.c b/kernel/fork.c
> index b64efec..076297a 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -11,7 +11,22 @@
> * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
> */
>
> +#include <linux/anon_inodes.h>
> #include <linux/slab.h>
> +#if 0
> +#include <linux/sched/autogroup.h>
> +#include <linux/sched/mm.h>
> +#include <linux/sched/coredump.h>
> +#include <linux/sched/user.h>
> +#include <linux/sched/numa_balancing.h>
> +#include <linux/sched/stat.h>
> +#include <linux/sched/task.h>
> +#include <linux/sched/task_stack.h>
> +#include <linux/sched/cputime.h>
> +#include <linux/seq_file.h>
> +#include <linux/rtmutex.h>
> +>>>>>>> b3e58382... clone: add CLONE_PIDFD
> +#endif

That looks odd :(

Can you please refresh this patch series, and make sure it is correct
and resend it?

thanks,

greg k-h