From mboxrd@z Thu Jan 1 00:00:00 1970 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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 8A251C433DF for ; Tue, 9 Jun 2020 00:31:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 66AC320760 for ; Tue, 9 Jun 2020 00:31:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591662714; bh=6tDz6kz3EWPvtiMKUTe9UWYLirmxVR7ibzaVILkuUvg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=XiD008HmcIXWkNNZRYMp7zeYTZVYMHANTXbQchgsfLHhr6Vf61pfBxka4xlLqbbtg uhA6W8uky141xmANoDk5hTxuG5qj8MqgWII7ayIXvZxLyVlENK/brDn1jyV87NqohF bEe8M0+uFf0B9fpmtnMez2RC0AkRvZvKXKg83KTQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730295AbgFIAbv (ORCPT ); Mon, 8 Jun 2020 20:31:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:36358 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730031AbgFHXPZ (ORCPT ); Mon, 8 Jun 2020 19:15:25 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 853DA2076A; Mon, 8 Jun 2020 23:15:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591658125; bh=6tDz6kz3EWPvtiMKUTe9UWYLirmxVR7ibzaVILkuUvg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pLrAYinYQ1fy7K92Z6S1ikd/09nbUBxo6s+mqNwRHdYrRku9csj9bVz57tqD+TiXL E0Z/qYG8FvPXzQylJgABHXqxFqRVz3ZMezSriEz9wkglS6y4C65z82EmauRHAMgIfa H4PdABZ9V1OtliWlCRKgOYy+nNAjWGF9kypRNfkw= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Ilya Dryomov , Petr Mladek , Sergey Senozhatsky , Andy Shevchenko , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman Subject: [PATCH AUTOSEL 5.6 161/606] vsprintf: don't obfuscate NULL and error pointers Date: Mon, 8 Jun 2020 19:04:46 -0400 Message-Id: <20200608231211.3363633-161-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200608231211.3363633-1-sashal@kernel.org> References: <20200608231211.3363633-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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(-) diff --git a/lib/test_printf.c b/lib/test_printf.c index 2d9f520d2f27..6b1622f4d7c2 100644 --- 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 *p) 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(); diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 532b6606a18a..7c47ad52ce2f 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -794,6 +794,13 @@ static char *ptr_to_id(char *buf, char *end, const void *ptr, 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); -- 2.25.1