From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757612AbbCCXaV (ORCPT ); Tue, 3 Mar 2015 18:30:21 -0500 Received: from mail-lb0-f177.google.com ([209.85.217.177]:33098 "EHLO mail-lb0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756839AbbCCXU6 (ORCPT ); Tue, 3 Mar 2015 18:20:58 -0500 From: Rasmus Villemoes To: Andrew Morton , Andy Shevchenko , Rasmus Villemoes , "Peter Zijlstra (Intel)" , Tejun Heo Cc: linux-kernel@vger.kernel.org Subject: [PATCH v4 1/3] lib/vsprintf.c: Fix potential NULL deref in hex_string Date: Wed, 4 Mar 2015 00:20:33 +0100 Message-Id: <1425424836-17947-2-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.1.3 In-Reply-To: <1425424836-17947-1-git-send-email-linux@rasmusvillemoes.dk> References: <1423525491-12613-1-git-send-email-linux@rasmusvillemoes.dk> <1425424836-17947-1-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. Acked-by: Andy Shevchenko 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 b235c96167d3..a1b6487c6710 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -783,11 +783,19 @@ 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