The patch titled
Subject: docs: proc: add documentation for "hidepid=4" and "subset=pid" options and new mount behavior
has been added to the -mm tree. Its filename is
docs-proc-add-documentation-for-hidepid=4-and-subset=pid-options-and-new-mount-behavior.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/docs-proc-add-documentation-for-hidepid%3D4-and-subset%3Dpid-options-and-new-mount-behavior.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/docs-proc-add-documentation-for-hidepid%3D4-and-subset%3Dpid-options-and-new-mount-behavior.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Alexey Gladkov <gladkov.alexey@xxxxxxxxx>
Subject: docs: proc: add documentation for "hidepid=4" and "subset=pid" options and new mount behavior
Link: http://lkml.kernel.org/r/20200419141057.621356-6-gladkov.alexey@xxxxxxxxx
Signed-off-by: Alexey Gladkov <gladkov.alexey@xxxxxxxxx>
Reviewed-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Daniel Micay <danielmicay@xxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Djalal Harouni <tixxdz@xxxxxxxxx>
Cc: "Dmitry V . Levin" <ldv@xxxxxxxxxxxx>
Cc: "Eric W . Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "J . Bruce Fields" <bfields@xxxxxxxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/proc.rst | 54 +++++++++++++++++++++++++++
1 file changed, 54 insertions(+)
--- a/Documentation/filesystems/proc.rst~docs-proc-add-documentation-for-hidepid=4-and-subset=pid-options-and-new-mount-behavior
+++ a/Documentation/filesystems/proc.rst
@@ -51,6 +51,8 @@ fixes/update part 1.1 Stefani Seibold <
4 Configuring procfs
4.1 Mount options
+ 5 Filesystem behavior
+
Preface
=======
@@ -2142,6 +2144,7 @@ The following mount options are supporte
========= ========================================================
hidepid= Set /proc/<pid>/ access mode.
gid= Set the group authorized to learn processes information.
+ subset= Show only the specified subset of procfs.
========= ========================================================
hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
@@ -2164,6 +2167,57 @@ information about running processes, whe
privileges, whether other user runs some sensitive program, whether other users
run any program at all, etc.
+hidepid=4 means that procfs should only contain /proc/<pid>/ directories
+that the caller can ptrace.
+
gid= defines a group authorized to learn processes information otherwise
prohibited by hidepid=. If you use some daemon like identd which needs to learn
information about processes information, just add identd to this group.
+
+subset=pid hides all top level files and directories in the procfs that
+are not related to tasks.
+
+5 Filesystem behavior
+----------------------------
+
+Originally, before the advent of pid namepsace, procfs was a global file
+system. It means that there was only one procfs instance in the system.
+
+When pid namespace was added, a separate procfs instance was mounted in
+each pid namespace. So, procfs mount options are global among all
+mountpoints within the same namespace.
+
+::
+
+# grep ^proc /proc/mounts
+proc /proc proc rw,relatime,hidepid=2 0 0
+
+# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
+mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
++++ exited with 0 +++
+
+# grep ^proc /proc/mounts
+proc /proc proc rw,relatime,hidepid=2 0 0
+proc /tmp/proc proc rw,relatime,hidepid=2 0 0
+
+and only after remounting procfs mount options will change at all
+mountpoints.
+
+# mount -o remount,hidepid=1 -t proc proc /tmp/proc
+
+# grep ^proc /proc/mounts
+proc /proc proc rw,relatime,hidepid=1 0 0
+proc /tmp/proc proc rw,relatime,hidepid=1 0 0
+
+This behavior is different from the behavior of other filesystems.
+
+The new procfs behavior is more like other filesystems. Each procfs mount
+creates a new procfs instance. Mount options affect own procfs instance.
+It means that it became possible to have several procfs instances
+displaying tasks with different filtering options in one pid namespace.
+
+# mount -o hidepid=2 -t proc proc /proc
+# mount -o hidepid=1 -t proc proc /tmp/proc
+# grep ^proc /proc/mounts
+proc /proc proc rw,relatime,hidepid=2 0 0
+proc /tmp/proc proc rw,relatime,hidepid=1 0 0
_
Patches currently in -mm which might be from gladkov.alexey@xxxxxxxxx are
proc-rename-struct-proc_fs_info-to-proc_fs_opts.patch
proc-allow-to-mount-many-instances-of-proc-in-one-pid-namespace.patch
proc-instantiate-only-pids-that-we-can-ptrace-on-hidepid=4-mount-option.patch
proc-add-option-to-mount-only-a-pids-subset.patch
docs-proc-add-documentation-for-hidepid=4-and-subset=pid-options-and-new-mount-behavior.patch
proc-use-human-readable-values-for-hidepid.patch
proc-use-named-enums-for-better-readability.patch
