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Subject[PATCH v5 1/5] docs: proc: add documentation about mount restrictions
Date
Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
Documentation/filesystems/proc.rst | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 2fa69f710e2a..3daf0e7d1071 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -50,6 +50,7 @@ fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009

4 Configuring procfs
4.1 Mount options
+ 4.2 Mount restrictions

5 Filesystem behavior

@@ -2175,6 +2176,21 @@ 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.

+4.2 Mount restrictions
+--------------------------
+
+The procfs can be mounted without any special restrictions if user namespace is
+not used. You only need to have permission to mount (CAP_SYS_ADMIN).
+
+If you are inside the user namespace, the kernel checks the instances of procfs
+available to you and will not allow procfs to be mounted if:
+
+ 1. There is a bind mount of part of procfs visible. Whoever mounts should be
+ able to see the entire filesystem.
+ 2. Mount is prohibited if a new mount overrides the readonly option or family
+ of atime options.
+ 3. If any file or non-empty procfs directory is hidden by another filesystem.
+
Chapter 5: Filesystem behavior
==============================

--
2.29.2
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