linux-kernel - [ 064/105] kernel/sys.c: fix stack memory content leak via UNAME26

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Message-Id: <20121028231556.720251581@decadent.org.uk>
Date:	Sun, 28 Oct 2012 23:16:40 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Kees Cook <keescook@...omium.org>,
	PaX Team <pageexec@...email.hu>,
	Andi Kleen <ak@...ux.intel.com>,
	Brad Spengler <spender@...ecurity.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 064/105] kernel/sys.c: fix stack memory content leak via UNAME26

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@...omium.org>

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).

CVE-2012-0957

Reported-by: PaX Team <pageexec@...email.hu>
Signed-off-by: Kees Cook <keescook@...omium.org>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: PaX Team <pageexec@...email.hu>
Cc: Brad Spengler <spender@...ecurity.net>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/sys.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index c5cb5b9..01865c6 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)
 			rest++;
 		}
 		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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