From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933956AbbKSKL6 (ORCPT ); Thu, 19 Nov 2015 05:11:58 -0500 Received: from mail-wm0-f46.google.com ([74.125.82.46]:34902 "EHLO mail-wm0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758210AbbKSKLz (ORCPT ); Thu, 19 Nov 2015 05:11:55 -0500 From: Rasmus Villemoes To: Andy Shevchenko Cc: Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 5/7] test_hexdump: check all bytes in real buffer Organization: D03 References: <1447259718-19647-1-git-send-email-andriy.shevchenko@linux.intel.com> <1447259718-19647-6-git-send-email-andriy.shevchenko@linux.intel.com> X-Hashcash: 1:20:151119:andriy.shevchenko@linux.intel.com::4DHCl21RKVX+BQFB:00000000000000000000000000000dQv X-Hashcash: 1:20:151119:linux-kernel@vger.kernel.org::rBGaXcrp6Kwr9LRx:000000000000000000000000000000000KdGv X-Hashcash: 1:20:151119:akpm@linux-foundation.org::LenwIWvhZjlXwWyS:000000000000000000000000000000000000KoMs Date: Thu, 19 Nov 2015 11:11:51 +0100 In-Reply-To: <1447259718-19647-6-git-send-email-andriy.shevchenko@linux.intel.com> (Andy Shevchenko's message of "Wed, 11 Nov 2015 18:35:16 +0200") Message-ID: <87lh9us3h4.fsf@rasmusvillemoes.dk> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 11 2015, Andy Shevchenko wrote: > After processing by hex_dump_to_buffer() check all the parts to be expected. > > Part 1. The actual expected hex dump with or without ASCII part. > This is provided by plain strcmp() call including check for the > terminating NUL. > > Part 2. Check if the buffer is dirty beyond needed. > We fill the buffer by ' ' (space) characters, so, we expect to have the > tail of buffer will be left untouched. Check all bytes in the tail of > the buffer. First of all, ' ' is one of the characters which hexdump is certainly supposed to spit out, so I think it's better to use some other character for prefilling. Otherwise we wouldn't be able to detect a stray write of a space which wasn't properly guarded by a size check. I'd suggest '\xff' or any other non-ascii character (and make it a #define so that it's less magic). > Part 3. Return code should be as expected. > > Signed-off-by: Andy Shevchenko > --- > lib/test_hexdump.c | 32 ++++++++++++++++---------------- > 1 file changed, 16 insertions(+), 16 deletions(-) > > diff --git a/lib/test_hexdump.c b/lib/test_hexdump.c > index a3e3b01..9b95b67 100644 > --- a/lib/test_hexdump.c > +++ b/lib/test_hexdump.c > @@ -128,10 +128,9 @@ static void __init test_hexdump_set(int rowsize, bool ascii) > > static void __init test_hexdump_overflow(size_t buflen, bool ascii) > { > + char test[TEST_HEXDUMP_BUF_SIZE]; > char buf[TEST_HEXDUMP_BUF_SIZE]; > - const char *t = test_data_1_le[0]; > size_t len = 1; > - size_t l = buflen; > int rs = 16, gs = 1; > int ae, he, e, r; > bool a; > @@ -147,26 +146,27 @@ static void __init test_hexdump_overflow(size_t buflen, bool ascii) > e = ae; > else > e = he; > - buf[e + 2] = '\0'; > > if (!buflen) { > - a = r == e && buf[0] == ' '; > - } else if (l < 3) { > - a = r == e && buf[0] == '\0'; > - } else if (l < 4) { > - a = r == e && !strcmp(buf, t); > - } else if (ascii) { > - if (l < 51) > - a = r == e && buf[l - 1] == '\0' && buf[l - 2] == ' '; > - else > - a = r == e && buf[50] == '\0' && buf[49] == '.'; > + memset(test, ' ', sizeof(test)); > + test[sizeof(buf) - 1] = '\0'; > + > + a = r == e && !memchr_inv(buf, ' ', sizeof(buf)); test and buf happen to have the same size, but "test[sizeof(buf) - 1] = '\0'" is rather odd. But you don't even seem to use test in this branch? > } else { > - a = r == e && buf[e] == '\0'; > + int f = min_t(int, e + 1, buflen); > + > + test_hexdump_prepare_test(len, rs, gs, test, sizeof(test), ascii); > + test[f - 1] = '\0'; > + > + a = r == e && !memchr_inv(buf + f, ' ', sizeof(buf) - f) && !strcmp(buf, test); > } There's also a bit of duplication in the !buflen and buflen branches. Why not pull the computation of f (the number of expected bytes written) outside and do f = min_t(int, e + 1, buflen); a = r == e && !memchr_inv(buf + f, ' ', sizeof(buf) - f); if (buflen) { test_hexdump_prepare_test(len, rs, gs, test, sizeof(test), ascii); test[f - 1] = '\0'; a = a && !memcmp(buf, test, f); } (I think it's better to use memcmp for "untrusted" buffers - if hexdump didn't make buf into a proper C string, it's a little fragile passing it to strcmp). This makes it obvious that the entire contents of buf is being tested. Rasmus