Date:   Mon, 4 Jan 2021 14:03:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Wen Yang <wenyang@...ux.alibaba.com>
Cc:     Sasha Levin <sashal@...nel.org>,
        Xunlei Pang <xlpang@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org,
        Christian Brauner <christian@...uner.io>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Howells <dhowells@...hat.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Andy Lutomirsky <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Al Viro <viro@...iv.linux.org.uk>, stable@...r.kernel.org
Subject: Re: [PATCH 01/10] clone: add CLONE_PIDFD

On Fri, Dec 04, 2020 at 02:31:55AM +0800, Wen Yang wrote:
> From: Christian Brauner <christian@...uner.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@...ux-foundation.org>
> Signed-off-by: Christian Brauner <christian@...uner.io>
> Co-developed-by: Jann Horn <jannh@...gle.com>
> Signed-off-by: Jann Horn <jannh@...gle.com>
> Reviewed-by: Oleg Nesterov <oleg@...hat.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: David Howells <dhowells@...hat.com>
> Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
> Cc: Andy Lutomirsky <luto@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Aleksa Sarai <cyphar@...har.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: <stable@...r.kernel.org> # 4.9.x
> (clone: fix up cherry-pick conflicts for b3e583825266)
> Signed-off-by: Wen Yang <wenyang@...ux.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

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