linux-kernel - [PATCH 3.12 094/119] fix minor infoleak in get_user

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Date:   Thu, 29 Sep 2016 12:25:30 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 094/119] fix minor infoleak in get_user_ex()

From: Al Viro <viro@...IV.linux.org.uk>

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

===============

commit 1c109fabbd51863475cd12ac206bdd249aee35af upstream.

get_user_ex(x, ptr) should zero x on failure.  It's not a lot of a leak
(at most we are leaking uninitialized 64bit value off the kernel stack,
and in a fairly constrained situation, at that), but the fix is trivial,
so...

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
[ This sat in different branch from the uaccess fixes since mid-August ]
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/x86/include/asm/uaccess.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 5838fa911aa0..01635e4e187a 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -383,7 +383,11 @@ do {									\
 #define __get_user_asm_ex(x, addr, itype, rtype, ltype)			\
 	asm volatile("1:	mov"itype" %1,%"rtype"0\n"		\
 		     "2:\n"						\
-		     _ASM_EXTABLE_EX(1b, 2b)				\
+		     ".section .fixup,\"ax\"\n"				\
+                     "3:xor"itype" %"rtype"0,%"rtype"0\n"		\
+		     "  jmp 2b\n"					\
+		     ".previous\n"					\
+		     _ASM_EXTABLE_EX(1b, 3b)				\
 		     : ltype(x) : "m" (__m(addr)))
 
 #define __put_user_nocheck(x, ptr, size)			\
-- 
2.10.0