From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753267AbbJTUbZ (ORCPT ); Tue, 20 Oct 2015 16:31:25 -0400 Received: from mail-lf0-f54.google.com ([209.85.215.54]:34998 "EHLO mail-lf0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753161AbbJTUam (ORCPT ); Tue, 20 Oct 2015 16:30:42 -0400 From: Rasmus Villemoes To: Andrew Morton Cc: Rasmus Villemoes , linux-kernel@vger.kernel.org Subject: [PATCH 13/13] lib/kasprintf.c: add sanity check to kvasprintf Date: Tue, 20 Oct 2015 22:30:13 +0200 Message-Id: <1445373013-20207-14-git-send-email-linux@rasmusvillemoes.dk> X-Mailer: git-send-email 2.6.1 In-Reply-To: <1445373013-20207-1-git-send-email-linux@rasmusvillemoes.dk> References: <1445373013-20207-1-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 32f12150fc4f..a30bf3042020 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