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Date:	Wed,  2 Mar 2011 21:07:54 -0500
From:	Stephen Wilson <>
To:	Andrew Morton <>
Cc:	Al Viro <>,
	David Rientjes <>,
	KOSAKI Motohiro <>,
	Nick Piggin <>,
	Roland McGrath <>,, Stephen Wilson <>
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

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 <>
 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:
 	return copied;
 loff_t mem_lseek(struct file *file, loff_t offset, int orig)

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