From: Chen Gang Subject: Re: [PATCH] target-ppc: kvm: Fix memory overflow issue about strncat() Date: Mon, 13 Oct 2014 23:43:43 +0800 Message-ID: <543BF32F.4020205@gmail.com> References: <543BE352.3080609@gmail.com> <543BE616.1000707@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: qemu-ppc@nongnu.org, kvm@vger.kernel.org, qemu-devel , qemu-trivial@nongnu.org To: Alexander Graf , pbonzini@redhat.com Return-path: Received: from mail-pa0-f45.google.com ([209.85.220.45]:59610 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752734AbaJMPhw (ORCPT ); Mon, 13 Oct 2014 11:37:52 -0400 Received: by mail-pa0-f45.google.com with SMTP id rd3so6047177pab.18 for ; Mon, 13 Oct 2014 08:37:52 -0700 (PDT) In-Reply-To: <543BE616.1000707@suse.de> Sender: kvm-owner@vger.kernel.org List-ID: On 10/13/14 22:47, Alexander Graf wrote: > > Could you please instead rewrite it to use g_strdup_printf() rather than > strncat()s? That way we resolve all string pitfalls automatically - and > this code is not the fast path, so doing an extra memory allocation is ok. > I guess, it is a personal taste. For me, it may need additional variable for g_strdup_printf(), and not save code lines, but *sprintf() is more readable than str*cat(). The related code may like below (welcome any improvement for it): diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c index 66e7ce5..cea6a87 100644 --- a/target-ppc/kvm.c +++ b/target-ppc/kvm.c @@ -1782,7 +1782,7 @@ static int kvmppc_find_cpu_dt(char *buf, int buf_len) * format) */ static uint64_t kvmppc_read_int_cpu_dt(const char *propname) { - char buf[PATH_MAX]; + char buf[PATH_MAX], *tmp; union { uint32_t v32; uint64_t v64; @@ -1794,10 +1794,10 @@ static uint64_t kvmppc_read_int_cpu_dt(const char *propname) return -1; } - strncat(buf, "/", sizeof(buf) - strlen(buf) - 1); - strncat(buf, propname, sizeof(buf) - strlen(buf) - 1); + tmp = g_strdup_printf("%s/%s", buf, propname); - f = fopen(buf, "rb"); + f = fopen(tmp, "rb"); + g_free(buf); if (!f) { return -1; } For me, it is really a personal taste, so if the maintainer feels the diff above is OK, I shall send patch v2 for it within 2 days. Thanks. -- Chen Gang Open, share, and attitude like air, water, and life which God blessed