From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750979AbdHSETz (ORCPT ); Sat, 19 Aug 2017 00:19:55 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:36384 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750716AbdHSETx (ORCPT ); Sat, 19 Aug 2017 00:19:53 -0400 From: "Lee, Chun-Yi" X-Google-Original-From: "Lee, Chun-Yi" To: David Howells Cc: linux-kernel@vger.kernel.org, "Lee, Chun-Yi" , Rusty Russell , Takashi Iwai , Pawel Wieczorkiewicz Subject: [PATCH] X.509: Fix the buffer overflow in the utility function for OID string Date: Sat, 19 Aug 2017 12:19:44 +0800 Message-Id: <20170819041944.11855-1-jlee@suse.com> X-Mailer: git-send-email 2.10.2 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Takashi Iwai The sprint_oid() utility function doesn't properly check the buffer size that it causes that the warning in vsnprintf() be triggered. For example on v4.1 kernel: [ 49.612536] ------------[ cut here ]------------ [ 49.612543] WARNING: CPU: 0 PID: 2357 at lib/vsprintf.c:1867 vsnprintf+0x5a7/0x5c0() ... We can trigger this issue by injecting maliciously crafted x509 cert in DER format. Just using hex editor to change the length of OID to over the length of the SEQUENCE container. For example: 0:d=0 hl=4 l= 980 cons: SEQUENCE 4:d=1 hl=4 l= 700 cons: SEQUENCE 8:d=2 hl=2 l= 3 cons: cont [ 0 ] 10:d=3 hl=2 l= 1 prim: INTEGER :02 13:d=2 hl=2 l= 9 prim: INTEGER :9B47FAF791E7D1E3 24:d=2 hl=2 l= 13 cons: SEQUENCE 26:d=3 hl=2 l= 9 prim: OBJECT :sha256WithRSAEncryption 37:d=3 hl=2 l= 0 prim: NULL 39:d=2 hl=2 l= 121 cons: SEQUENCE 41:d=3 hl=2 l= 22 cons: SET 43:d=4 hl=2 l= 20 cons: SEQUENCE <=== the SEQ length is 20 45:d=5 hl=2 l= 3 prim: OBJECT :organizationName <=== the original length is 3, change the length of OID to over the length of SEQUENCE Pawel Wieczorkiewicz reported this problem and Takashi Iwai provided patch to fix it by checking the bufsize in sprint_oid(). From: Takashi Iwai Reported-by: Pawel Wieczorkiewicz Cc: David Howells Cc: Rusty Russell Cc: Takashi Iwai Cc: Pawel Wieczorkiewicz Signed-off-by: "Lee, Chun-Yi" --- lib/oid_registry.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/lib/oid_registry.c b/lib/oid_registry.c index 318f382..41b9e50 100644 --- a/lib/oid_registry.c +++ b/lib/oid_registry.c @@ -142,9 +142,9 @@ int sprint_oid(const void *data, size_t datasize, char *buffer, size_t bufsize) } ret += count = snprintf(buffer, bufsize, ".%lu", num); buffer += count; - bufsize -= count; - if (bufsize == 0) + if (bufsize <= count) return -ENOBUFS; + bufsize -= count; } return ret; -- 2.10.2