linux-kernel - [PATCH] Enable writing to /proc/PID/mem.

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Message-Id: <1299118074-13342-1-git-send-email-wilsons@start.ca>
Date:	Wed,  2 Mar 2011 21:07:54 -0500
From:	Stephen Wilson <wilsons@...rt.ca>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Nick Piggin <npiggin@...nel.dk>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, Stephen Wilson <wilsons@...rt.ca>
Subject: [PATCH] Enable writing to /proc/PID/mem.

For a long time /proc/PID/mem has provided a read-only interface, at least since
2.4.0.  However, a write capability has existed "forever" in tree via the
function mem_write, disabled with an #ifdef along with the comment "this is a
security hazard".  Charles Wright, back in 2006, gave some history on the
subject:

    http://lkml.org/lkml/2006/3/10/224

Later, in commit 638fa202c, Roland McGrath updated mem_write to call
check_mem_permission which ensures an identical security policy for
/proc/PID/mem as for ptrace().  IOW, the proc interface provides a simpler, more
efficient, but otherwise equivalent mechanism for probing a processes memory as
available via ptrace.

There is no longer a security hazard and the world can safely use read/write
instead of ptrace PEEK/POKE's.  Remove the #ifdef.

Signed-off-by: Stephen Wilson <wilsons@...rt.ca>
---
 fs/proc/base.c |    5 -----
 1 files changed, 0 insertions(+), 5 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9d096e8..70fc4db 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -829,10 +829,6 @@ out_no_task:
 	return ret;
 }

-#define mem_write NULL
-
-#ifndef mem_write
-/* This is a security hazard */
 static ssize_t mem_write(struct file * file, const char __user *buf,
 			 size_t count, loff_t *ppos)
 {
@@ -880,7 +876,6 @@ out:
 out_no_task:
 	return copied;
 }
-#endif

 loff_t mem_lseek(struct file *file, loff_t offset, int orig)
 {
-- 
1.7.3.5

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