From patchwork Tue May 26 18:53:39 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 225342 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9CD9AC433DF for ; Tue, 26 May 2020 19:14:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 791AE208B6 for ; Tue, 26 May 2020 19:14:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590520444; bh=kQNd34cmik6TcoAVHlkHhkO1e2MtsAltfeIAfLZeifU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=aV2+qA154EsWoNM/z+LCsJrHa6dmKXG0XTi87UIB4URLUxgFMPSLnKOsbumj/kwWv K8xiTrCsuD2O/rJy2xJXcEjltvTbL6A5zikkNY/qPVlx55VKN+P18o3rkCg5gaOMO5 l1Hgj1kjc9mkM2IoYlQ8NJS4HqKPN3feR7DaQ68Q= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392056AbgEZTOD (ORCPT ); Tue, 26 May 2020 15:14:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:44664 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392026AbgEZTOC (ORCPT ); Tue, 26 May 2020 15:14:02 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8560F208B8; Tue, 26 May 2020 19:14:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590520442; bh=kQNd34cmik6TcoAVHlkHhkO1e2MtsAltfeIAfLZeifU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lj+UKqLujONiQuQXsWupvvedgmX00pPnn2hccHHUiIu2CWcQ3DpDovoaiAsgJIXV3 ZLHRtHPizZATjvsW11bkdHTEdHgdRiCqFOtLQNDpaXw4DtK6iVXbJYUCyPGiZwxr75 nsXMs2wDI7sEQsVs/1VSksQaNE1o+vDI1HJuAspY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ilya Dryomov , Petr Mladek , Sergey Senozhatsky , Andy Shevchenko , "Steven Rostedt (VMware)" , Linus Torvalds Subject: [PATCH 5.6 082/126] vsprintf: dont obfuscate NULL and error pointers Date: Tue, 26 May 2020 20:53:39 +0200 Message-Id: <20200526183944.975389852@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200526183937.471379031@linuxfoundation.org> References: <20200526183937.471379031@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Ilya Dryomov commit 7bd57fbc4a4ddedc664cad0bbced1b469e24e921 upstream. I don't see what security concern is addressed by obfuscating NULL and IS_ERR() error pointers, printed with %p/%pK. Given the number of sites where %p is used (over 10000) and the fact that NULL pointers aren't uncommon, it probably wouldn't take long for an attacker to find the hash that corresponds to 0. Although harder, the same goes for most common error values, such as -1, -2, -11, -14, etc. The NULL part actually fixes a regression: NULL pointers weren't obfuscated until commit 3e5903eb9cff ("vsprintf: Prevent crash when dereferencing invalid pointers") which went into 5.2. I'm tacking the IS_ERR() part on here because error pointers won't leak kernel addresses and printing them as pointers shouldn't be any different from e.g. %d with PTR_ERR_OR_ZERO(). Obfuscating them just makes debugging based on existing pr_debug and friends excruciating. Note that the "always print 0's for %pK when kptr_restrict == 2" behaviour which goes way back is left as is. Example output with the patch applied: ptr error-ptr NULL %p: 0000000001f8cc5b fffffffffffffff2 0000000000000000 %pK, kptr = 0: 0000000001f8cc5b fffffffffffffff2 0000000000000000 %px: ffff888048c04020 fffffffffffffff2 0000000000000000 %pK, kptr = 1: ffff888048c04020 fffffffffffffff2 0000000000000000 %pK, kptr = 2: 0000000000000000 0000000000000000 0000000000000000 Fixes: 3e5903eb9cff ("vsprintf: Prevent crash when dereferencing invalid pointers") Signed-off-by: Ilya Dryomov Reviewed-by: Petr Mladek Reviewed-by: Sergey Senozhatsky Reviewed-by: Andy Shevchenko Acked-by: Steven Rostedt (VMware) Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- lib/test_printf.c | 19 ++++++++++++++++++- lib/vsprintf.c | 7 +++++++ 2 files changed, 25 insertions(+), 1 deletion(-) --- a/lib/test_printf.c +++ b/lib/test_printf.c @@ -214,6 +214,7 @@ test_string(void) #define PTR_STR "ffff0123456789ab" #define PTR_VAL_NO_CRNG "(____ptrval____)" #define ZEROS "00000000" /* hex 32 zero bits */ +#define ONES "ffffffff" /* hex 32 one bits */ static int __init plain_format(void) @@ -245,6 +246,7 @@ plain_format(void) #define PTR_STR "456789ab" #define PTR_VAL_NO_CRNG "(ptrval)" #define ZEROS "" +#define ONES "" static int __init plain_format(void) @@ -330,14 +332,28 @@ test_hashed(const char *fmt, const void test(buf, fmt, p); } +/* + * NULL pointers aren't hashed. + */ static void __init null_pointer(void) { - test_hashed("%p", NULL); + test(ZEROS "00000000", "%p", NULL); test(ZEROS "00000000", "%px", NULL); test("(null)", "%pE", NULL); } +/* + * Error pointers aren't hashed. + */ +static void __init +error_pointer(void) +{ + test(ONES "fffffff5", "%p", ERR_PTR(-11)); + test(ONES "fffffff5", "%px", ERR_PTR(-11)); + test("(efault)", "%pE", ERR_PTR(-11)); +} + #define PTR_INVALID ((void *)0x000000ab) static void __init @@ -649,6 +665,7 @@ test_pointer(void) { plain(); null_pointer(); + error_pointer(); invalid_pointer(); symbol_ptr(); kernel_ptr(); --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -794,6 +794,13 @@ static char *ptr_to_id(char *buf, char * unsigned long hashval; int ret; + /* + * Print the real pointer value for NULL and error pointers, + * as they are not actual addresses. + */ + if (IS_ERR_OR_NULL(ptr)) + return pointer_string(buf, end, ptr, spec); + /* When debugging early boot use non-cryptographically secure hash. */ if (unlikely(debug_boot_weak_hash)) { hashval = hash_long((unsigned long)ptr, 32);