From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754055AbbLCUvm (ORCPT ); Thu, 3 Dec 2015 15:51:42 -0500 Received: from mail-lb0-f182.google.com ([209.85.217.182]:35926 "EHLO mail-lb0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753795AbbLCUvj (ORCPT ); Thu, 3 Dec 2015 15:51:39 -0500 From: Rasmus Villemoes To: Andrew Morton , Rasmus Villemoes Cc: linux-kernel@vger.kernel.org Subject: [PATCH v3 07/14] lib/kasprintf.c: add sanity check to kvasprintf Date: Thu, 3 Dec 2015 21:51:06 +0100 Message-Id: <1449175873-1780-8-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.6.1 In-Reply-To: <1449175873-1780-1-git-send-email-linux@rasmusvillemoes.dk> References: <1449175873-1780-1-git-send-email-linux@rasmusvillemoes.dk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org kasprintf relies on being able to replay the formatting and getting the same result (in particular, the same length). This will almost always work, but it is possible that the object pointed to by a %s or %p argument changed under us (so we might get truncated output). Add a somewhat paranoid sanity check and let's see if it ever triggers. Signed-off-by: Rasmus Villemoes --- lib/kasprintf.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/lib/kasprintf.c b/lib/kasprintf.c index f194e6e593e1..7f6c506a4942 100644 --- a/lib/kasprintf.c +++ b/lib/kasprintf.c @@ -13,19 +13,21 @@ /* Simplified asprintf. */ char *kvasprintf(gfp_t gfp, const char *fmt, va_list ap) { - unsigned int len; + unsigned int first, second; char *p; va_list aq; va_copy(aq, ap); - len = vsnprintf(NULL, 0, fmt, aq); + first = vsnprintf(NULL, 0, fmt, aq); va_end(aq); - p = kmalloc_track_caller(len+1, gfp); + p = kmalloc_track_caller(first+1, gfp); if (!p) return NULL; - vsnprintf(p, len+1, fmt, ap); + second = vsnprintf(p, first+1, fmt, ap); + WARN(first != second, "different return values (%u and %u) from vsnprintf(\"%s\", ...)", + first, second, fmt); return p; } -- 2.6.1