From owner-freebsd-hackers@freebsd.org Tue Nov 3 11:16:23 2020 Return-Path: Delivered-To: freebsd-hackers@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 5F075455056 for ; Tue, 3 Nov 2020 11:16:23 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from mailman.nyi.freebsd.org (unknown [127.0.1.3]) by mx1.freebsd.org (Postfix) with ESMTP id 4CQS071GC5z3VHS for ; Tue, 3 Nov 2020 11:16:23 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: by mailman.nyi.freebsd.org (Postfix) id 295274551AB; Tue, 3 Nov 2020 11:16:23 +0000 (UTC) Delivered-To: hackers@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 27D71455398 for ; Tue, 3 Nov 2020 11:16:23 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4CQS054r1Xz3VKY for ; Tue, 3 Nov 2020 11:16:21 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.16.1/8.16.1) with ESMTPS id 0A3BGEtt072261 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Tue, 3 Nov 2020 13:16:17 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua 0A3BGEtt072261 Received: (from kostik@localhost) by tom.home (8.16.1/8.16.1/Submit) id 0A3BGDdP072260; Tue, 3 Nov 2020 13:16:13 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 3 Nov 2020 13:16:13 +0200 From: Konstantin Belousov To: xtouqh@hotmail.com Cc: Hans Petter Selasky , hackers@freebsd.org Subject: Re: KASSERT(val != 0) not triggering in linux_errno.c reading outside of array Message-ID: <20201103111613.GP2654@kib.kiev.ua> References: <77d2eef0-9cc8-aa39-6d28-a7fb41e233ac@selasky.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on tom.home X-Rspamd-Queue-Id: 4CQS054r1Xz3VKY X-Spamd-Bar: / Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=gmail.com (policy=none); spf=softfail (mx1.freebsd.org: 2001:470:d5e7:1::1 is neither permitted nor denied by domain of kostikbel@gmail.com) smtp.mailfrom=kostikbel@gmail.com X-Spamd-Result: default: False [-0.75 / 15.00]; ARC_NA(0.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; FREEMAIL_FROM(0.00)[gmail.com]; NEURAL_HAM_LONG(-0.09)[-0.087]; MIME_GOOD(-0.10)[text/plain]; HAS_XAW(0.00)[]; NEURAL_HAM_MEDIUM(-0.85)[-0.849]; R_SPF_SOFTFAIL(0.00)[~all:c]; NEURAL_SPAM_SHORT(0.19)[0.191]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; SUBJECT_HAS_EXCLAIM(0.00)[]; FREEMAIL_TO(0.00)[hotmail.com]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:6939, ipnet:2001:470::/32, country:US]; RCVD_COUNT_TWO(0.00)[2]; MAILMAN_DEST(0.00)[hackers]; DMARC_POLICY_SOFTFAIL(0.10)[gmail.com : No valid SPF, No valid DKIM,none] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Nov 2020 11:16:23 -0000 On Tue, Nov 03, 2020 at 01:17:51PM +0300, xtouqh@hotmail.com wrote: > Hans Petter Selasky wrote: > > Hi, > > > > Should: > > > >         for (i = 1; i < sizeof(linux_errtbl); i++) { > > > > Be: > > > >         for (i = 1; i < sizeof(linux_errtbl)/sizeof(linux_errtbl[0]); > > i++) { > > > > > > Or: > > > >         for (i = 1; i < (int)nitems(linux_errtbl); i++) { > > That's right, and I added the same comment in the review. My question is > different though -- with the issue present, KASSERT() should have triggered > (there are 0 values with incorrect indexes, added printf() confirms that) > exposing the bug, but it does not -- WHY? -- I just want to understand > what's going on. I think this is a poster child for the current undefined behaviour treatment by compilers. You are accessing beyond array last element, and compiler can prove it, so it allowed to do anything.