From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933155AbbA2KFk (ORCPT ); Thu, 29 Jan 2015 05:05:40 -0500 Received: from mail-lb0-f176.google.com ([209.85.217.176]:35911 "EHLO mail-lb0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761233AbbA2KDn (ORCPT ); Thu, 29 Jan 2015 05:03:43 -0500 From: Rasmus Villemoes To: Andy Shevchenko , Andrew Morton , Jiri Kosina , Randy Dunlap , Fabian Frederick , Bjorn Helgaas , Ryan Mallon , Masanari Iida Cc: Rasmus Villemoes , linux-kernel@vger.kernel.org Subject: [PATCH v2 1/3] lib/vsprintf.c: Fix potential NULL deref in hex_string Date: Thu, 29 Jan 2015 11:03:18 +0100 Message-Id: <1422525801-26560-2-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.1.3 In-Reply-To: <1422525801-26560-1-git-send-email-linux@rasmusvillemoes.dk> References: <1422451543-12401-1-git-send-email-linux@rasmusvillemoes.dk> <1422525801-26560-1-git-send-email-linux@rasmusvillemoes.dk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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"). Nobody seems to be using %ph with kasprintf, but we might as well fix it before it hits someone. Signed-off-by: Rasmus Villemoes --- lib/vsprintf.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index ec337f64f52d..3568e3906777 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -782,11 +782,19 @@ 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; -- 2.1.3