diff options
author | Alexey Gladkov <gladkov.alexey@gmail.com> | 2020-04-19 16:10:55 +0200 |
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committer | Eric W. Biederman <ebiederm@xmission.com> | 2020-04-22 10:51:22 -0500 |
commit | 37e7647a7212336d8a3a34db2e7f7345a47ca7b3 (patch) | |
tree | 3d3c1b1313b827a70564c707200d42d061be5525 | |
parent | 6814ef2d992af09451bbeda4770daa204461329e (diff) |
docs: proc: add documentation for "hidepid=4" and "subset=pid" options and new mount behavior
Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
-rw-r--r-- | Documentation/filesystems/proc.rst | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 38b606991065..360486c7a992 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -51,6 +51,8 @@ fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009 4 Configuring procfs 4.1 Mount options + 5 Filesystem behavior + Preface ======= @@ -2142,6 +2144,7 @@ The following mount options are supported: ========= ======================================================== 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, whether some daemon runs with elevated 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 |