From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752315Ab3FDWlP (ORCPT ); Tue, 4 Jun 2013 18:41:15 -0400 Received: from 1wt.eu ([62.212.114.60]:35158 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751803Ab3FDWkt (ORCPT ); Tue, 4 Jun 2013 18:40:49 -0400 Message-Id: <20130604172131.011412905@1wt.eu> User-Agent: quilt/0.48-1 Date: Tue, 04 Jun 2013 19:21:47 +0200 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Kees Cook , Emese Revfy , PaX Team , Al Viro , Oleg Nesterov , "Eric W. Biederman" , Serge Hallyn , Julien Tinnes , Andrew Morton , Linus Torvalds , Greg Kroah-Hartman , Willy Tarreau Subject: [ 017/184] signal: always clear sa_restorer on execve In-Reply-To: <58df134a4b98edf5b0073e2e1e988fe6@local> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.32-longterm review patch. If anyone has any objections, please let me know. ------------------ From: Kees Cook commit 2ca39528c01a933f6689cd6505ce65bd6d68a530 upstream. When the new signal handlers are set up, the location of sa_restorer is not cleared, leaking a parent process's address space location to children. This allows for a potential bypass of the parent's ASLR by examining the sa_restorer value returned when calling sigaction(). Based on what should be considered "secret" about addresses, it only matters across the exec not the fork (since the VMAs haven't changed until the exec). But since exec sets SIG_DFL and keeps sa_restorer, this is where it should be fixed. Given the few uses of sa_restorer, a "set" function was not written since this would be the only use. Instead, we use __ARCH_HAS_SA_RESTORER, as already done in other places. Example of the leak before applying this patch: $ cat /proc/$$/maps ... 7fb9f3083000-7fb9f3238000 r-xp 00000000 fd:01 404469 .../libc-2.15.so ... $ ./leak ... 7f278bc74000-7f278be29000 r-xp 00000000 fd:01 404469 .../libc-2.15.so ... 1 0 (nil) 0x7fb9f30b94a0 2 4000000 (nil) 0x7f278bcaa4a0 3 4000000 (nil) 0x7f278bcaa4a0 4 0 (nil) 0x7fb9f30b94a0 ... [akpm@linux-foundation.org: use SA_RESTORER for backportability] Signed-off-by: Kees Cook Reported-by: Emese Revfy Cc: Emese Revfy Cc: PaX Team Cc: Al Viro Cc: Oleg Nesterov Cc: "Eric W. Biederman" Cc: Serge Hallyn Cc: Julien Tinnes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman Signed-off-by: Willy Tarreau --- kernel/signal.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/signal.c b/kernel/signal.c index 2494827..df993fd 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -320,6 +320,9 @@ flush_signal_handlers(struct task_struct *t, int force_default) if (force_default || ka->sa.sa_handler != SIG_IGN) ka->sa.sa_handler = SIG_DFL; ka->sa.sa_flags = 0; +#ifdef SA_RESTORER + ka->sa.sa_restorer = NULL; +#endif sigemptyset(&ka->sa.sa_mask); ka++; } -- 1.7.12.2.21.g234cd45.dirty