[ 3.5.yuz extended stable ] Patch "kernel/sys.c: fix stack memory content leak via UNAME26" has been added to staging queue

Herton Ronaldo Krzesinski herton.krzesinski at canonical.com
Wed Nov 21 05:09:38 UTC 2012

This is a note to let you know that I have just added a patch titled

    kernel/sys.c: fix stack memory content leak via UNAME26

to the linux-3.5.y-queue branch of the 3.5.yuz extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.yuz tree, see



>From b4b75e2ab32d987646d2de96743f04932ba87d35 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook at chromium.org>
Date: Fri, 19 Oct 2012 13:56:51 -0700
Subject: [PATCH] kernel/sys.c: fix stack memory content leak via UNAME26

commit 2702b1526c7278c4d65d78de209a465d4de2885e upstream.

Calling uname() with the UNAME26 personality set allows a leak of kernel
stack contents.  This fixes it by defensively calculating the length of
copy_to_user() call, making the len argument unsigned, and initializing
the stack buffer to zero (now technically unneeded, but hey, overkill).


Reported-by: PaX Team <pageexec at freemail.hu>
Signed-off-by: Kees Cook <keescook at chromium.org>
Cc: Andi Kleen <ak at linux.intel.com>
Cc: PaX Team <pageexec at freemail.hu>
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>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
 kernel/sys.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 0349bde..1b66408 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1265,15 +1265,16 @@ DECLARE_RWSEM(uts_sem);
  * Work around broken programs that cannot handle "Linux 3.0".
  * Instead we map 3.x to 2.6.40+x, so e.g. 3.0 would be 2.6.40
-static int override_release(char __user *release, int len)
+static int override_release(char __user *release, size_t len)
 	int ret = 0;
-	char buf[65];

 	if (current->personality & UNAME26) {
-		char *rest = UTS_RELEASE;
+		const char *rest = UTS_RELEASE;
+		char buf[65] = { 0 };
 		int ndots = 0;
 		unsigned v;
+		size_t copy;

 		while (*rest) {
 			if (*rest == '.' && ++ndots >= 3)
@@ -1283,8 +1284,9 @@ static int override_release(char __user *release, int len)
 		v = ((LINUX_VERSION_CODE >> 8) & 0xff) + 40;
-		snprintf(buf, len, "2.6.%u%s", v, rest);
-		ret = copy_to_user(release, buf, len);
+		copy = min(sizeof(buf), max_t(size_t, 1, len));
+		copy = scnprintf(buf, copy, "2.6.%u%s", v, rest);
+		ret = copy_to_user(release, buf, copy + 1);
 	return ret;

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