[hardy CVE 2/2] proc: protect mm start_code/end_code in /proc/pid/stat

[Andy Whitcroft]

From: Kees Cook <kees.cook at canonical.com>

While mm->start_stack was protected from cross-uid viewing (commit
f83ce3e6b02d5 ("proc: avoid information leaks to non-privileged
processes")), the start_code and end_code values were not.  This would
allow the text location of a PIE binary to leak, defeating ASLR.

Note that the value "1" is used instead of "0" for a protected value since
"ps", "killall", and likely other readers of /proc/pid/stat, take
start_code of "0" to mean a kernel thread and will misbehave.  Thanks to
Brad Spengler for pointing this out.

Addresses CVE-2011-0726

Signed-off-by: Kees Cook <kees.cook at canonical.com>
Cc: <stable at kernel.org>
Cc: Alexey Dobriyan <adobriyan at gmail.com>
Cc: David Howells <dhowells at redhat.com>
Cc: Eugene Teo <eugeneteo at kernel.sg>
Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
Cc: Brad Spengler <spender at grsecurity.net>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

(cherry picked from commit 5883f57ca0008ffc93e09cbb9847a1928e50c6f3)
CVE-2011-0726
BugLink: http://bugs.launchpad.net/bugs/799906
Signed-off-by: Andy Whitcroft <apw at canonical.com>
---
 fs/proc/array.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 87902dd..4bceea5 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -526,8 +526,8 @@ static int do_task_stat(struct task_struct *task, char *buffer, int whole)
 		vsize,
 		mm ? get_mm_rss(mm) : 0,
 		rsslim,
-		mm ? mm->start_code : 0,
-		mm ? mm->end_code : 0,
+		mm ? (permitted ? mm->start_code : 1) : 0,
+		mm ? (permitted ? mm->end_code : 1) : 0,
 		(permitted && mm) ? mm->start_stack : 0,
 		esp,
 		eip,
-- 
1.7.4.1