Re: [PATCH 1/2] prctl.2: Add PR_SET_MM option description

[Cyrill Gorcunov <gorcunov@openvz.org>]

On Wed, Mar 21, 2012 at 06:21:19AM +1300, Michael Kerrisk (man-pages) wrote:
> Hello Cyrill,
> 
> The PR_SET_MM operation adds a number of new error cases to prctl(2).
> Could you extend you patch to add these under ERRORS?
> 

Hi Michael,

here is an update on previous patch. Please take a look and
tell me what you think when you get time. Complains are welcome!

	Cyrill
---
>From 10dbf8dc2e40426c56a6d2a2414bcb9d3a0f5ff3 Mon Sep 17 00:00:00 2001
From: Cyrill Gorcunov <gorcunov@openvz.org>
Date: Wed, 21 Mar 2012 02:20:11 +0400
Subject: [PATCH] prctl.2: Update description for PR_SET_MM option

New feature PR_SET_MM_EXE_FILE added, also
error codes updated.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
---
 man2/prctl.2 |   70 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 69 insertions(+), 1 deletions(-)

diff --git a/man2/prctl.2 b/man2/prctl.2
index 7a50ac1..de15426 100644
--- a/man2/prctl.2
+++ b/man2/prctl.2
@@ -481,6 +481,30 @@ argument should provide the address of the vector.
 The
 .I arg4
 is the size of the vector.
+
+.BR PR_SET_MM_EXE_FILE
+to supersede
+.IR /proc/pid/exe
+symbolic link with a new one pointing to a new executable file
+which descriptor is provided provided in the
+.I arg3
+argument.
+The file descriptor should be obtaned with a regular
+.BR open (2)
+call.
+
+To change the symlink, one needs to unmap all existing
+executable memory areas being created by the kernel itself
+(for example the kernel usually creates at least one executable
+memory area for Elf file
+.IR \.text
+section).
+
+The second limitation is that such transition can be done once
+in a process life time.
+Any furter attempts will be rejected.
+This should help system administrators to monitor the unusual
+symlinks transitions over all process running in a system.
 .\"
 .SH "RETURN VALUE"
 On success,
@@ -515,7 +539,9 @@ is not recognized.
 is
 .BR PR_MCE_KILL
 or
-.BR PR_MCE_KILL_GET ,
+.BR PR_MCE_KILL_GET
+or
+.BR PR_SET_MM ,
 and unused
 .BR prctl ()
 arguments were not specified as zero.
@@ -563,6 +589,48 @@ is
 and the caller does not have the
 .B CAP_SETPCAP
 capability.
+.TP
+.B EPERM
+.I option
+is
+.BR PR_SET_MM ,
+and the caller does not have the
+.B CAP_SYS_RESOURCE
+capability.
+.TP
+.B EACCES
+.I option
+is
+.BR PR_SET_MM ,
+and the
+.I arg3
+is
+.BR PR_SET_MM_EXE_FILE ,
+the file is not executable one.
+.TP
+.B EBUSY
+.I option
+is
+.BR PR_SET_MM ,
+and the
+.I arg3
+is
+.BR PR_SET_MM_EXE_FILE ,
+the second attempt to change
+.I /proc/pid/exe
+symlink is prohibited.
+.TP
+.B EBADF
+.I option
+is
+.BR PR_SET_MM ,
+and the
+.I arg3
+is
+.BR PR_SET_MM_EXE_FILE ,
+the file descriptor passed in
+.I arg4
+is not found.
 .\" The following can't actually happen, because prctl() in
 .\" seccomp mode will cause SIGKILL.
 .\" .TP
-- 
1.7.7.6