From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755921AbbA1UVA (ORCPT ); Wed, 28 Jan 2015 15:21:00 -0500 Received: from mga02.intel.com ([134.134.136.20]:64857 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755870AbbA1UUy (ORCPT ); Wed, 28 Jan 2015 15:20:54 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.09,481,1418112000"; d="scan'208";a="669116724" Message-ID: <1422456824.31903.298.camel@linux.intel.com> Subject: Re: [PATCH 1/2] lib/vsprintf.c: Fix potential NULL deref in hex_string From: Andy Shevchenko To: Rasmus Villemoes Cc: Andrew Morton , Jiri Kosina , Randy Dunlap , Fabian Frederick , Bjorn Helgaas , Ryan Mallon , Masanari Iida , linux-kernel@vger.kernel.org Date: Wed, 28 Jan 2015 16:53:44 +0200 In-Reply-To: <1422451543-12401-2-git-send-email-linux@rasmusvillemoes.dk> References: <1422451543-12401-1-git-send-email-linux@rasmusvillemoes.dk> <1422451543-12401-2-git-send-email-linux@rasmusvillemoes.dk> Organization: Intel Finland Oy Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.9-1+b1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2015-01-28 at 14:25 +0100, Rasmus Villemoes wrote: > The helper hex_string() is broken in two ways. First, it doesn't > increment buf regardless of whether there is room to print, so callers > such as kasprintf() that try to probe the correct storage to allocate > will get a too small return value. But even worse, kasprintf() (and > likely anyone else trying to find the size of the result) pass NULL > for buf and 0 for size, so we also have end == NULL. But this means > that the end-1 in hex_string() is (char*)-1, so buf < end-1 is true > and we get a NULL pointer deref. I double-checked this with a trivial > kernel module that just did a kasprintf(GFP_KERNEL, "%14ph", > "CrashBoomBang"). Good catch, though I don't like the implementation of fix. What about the following? diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 8690798..47b36ddd 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -783,11 +783,20 @@ char *hex_string(char *buf, char *end, u8 *addr, struct printf_spec spec, if (spec.field_width > 0) len = min_t(int, spec.field_width, 64); - for (i = 0; i < len && buf < end - 1; i++) { - buf = hex_byte_pack(buf, addr[i]); + for (i = 0; i < len; i++) { + if (buf < end) + *buf = hex_asc_hi(addr[i]); + ++buf; + + if (buf < end) + *buf = hex_asc_lo(addr[i]); + ++buf; - if (buf < end && separator && i != len - 1) - *buf++ = separator; + if (separator && i != len - 1) { + if (buf < end) + *buf = separator; + ++buf; + } } return buf; > Nobody seems to be using %ph with kasprintf, but we might as well fix > it before it hits someone. -- Andy Shevchenko Intel Finland Oy