From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.9 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_NONE shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 45F981F461 for ; Fri, 6 Sep 2019 17:37:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2395238AbfIFRhJ (ORCPT ); Fri, 6 Sep 2019 13:37:09 -0400 Received: from cloud.peff.net ([104.130.231.41]:42296 "HELO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S2389271AbfIFRhJ (ORCPT ); Fri, 6 Sep 2019 13:37:09 -0400 Received: (qmail 21378 invoked by uid 109); 6 Sep 2019 17:37:09 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with SMTP; Fri, 06 Sep 2019 17:37:09 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 5289 invoked by uid 111); 6 Sep 2019 17:38:54 -0000 Received: from sigill.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.7) by peff.net (qpsmtpd/0.94) with (TLS_AES_256_GCM_SHA384 encrypted) ESMTPS; Fri, 06 Sep 2019 13:38:54 -0400 Authentication-Results: peff.net; auth=none Date: Fri, 6 Sep 2019 13:37:07 -0400 From: Jeff King To: Derrick Stolee Cc: Taylor Blau , git@vger.kernel.org, gitster@pobox.com Subject: Re: [PATCH 3/3] commit-graph.c: handle corrupt/missing trees Message-ID: <20190906173707.GF23181@sigill.intra.peff.net> References: <9fbd965e3892307bb5bb78952f017624fcc0b73a.1567720960.git.me@ttaylorr.com> <20190906061919.GA5122@sigill.intra.peff.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Fri, Sep 06, 2019 at 12:51:56PM -0400, Derrick Stolee wrote: > > This one in theory benefits lots of other callsites, too, since it means > > we'll actually return NULL instead of nonsense like "8". But grepping > > around for calls to this function, I found literally zero of them > > actually bother checking for a NULL result. So there are probably dozens > > of similar segfaults waiting to happen in other code paths. > > Discouraging. > > > > This is sort-of attributable to my 834876630b (get_commit_tree(): return > > NULL for broken tree, 2019-04-09). Before then it was a BUG(). However, > > that state was relatively short-lived. Before 7b8a21dba1 (commit-graph: > > lazy-load trees for commits, 2018-04-06), we'd have similarly returned > > NULL (and anyway, BUG() is clearly wrong since it's a data error). > > > > None of which argues against your patches, but it's kind of sad that the > > issue is present in so many code paths. I wonder if we could be handling > > this in a more central way, but I don't see how short of dying. > > This is due to the mechanical conversion from using commit->tree->oid to > get_commit_tree_oid(commit). Those consumers were not checking if the > tree pointer was NULL, either, but they probably assumed that the > parse_commit() call would have failed earlier. Now that we are using this > method (for performance reasons to avoid creating too many 'struct tree's) > it makes sense to convert some of them to checking the return value more > carefully. Right, none of this is new at all. We have historically been very loose about assuming that things like commit->tree were valid. And they _usually_ are. Even if we're missing the object on disk, lookup_tree() is happy to assign it a struct (unless the object was already seen as another type!). I think turning that case into an error from parse_commit() would cover a lot of cases easily, without forcing each caller to check for NULL. -Peff