From: Jim Meyering Date: Fri, 21 Dec 2007 23:33:15 GMT Subject: Re: [PATCH] Don't dereference NULL upon lookup_tree failure. Message-ID: <87bq8jvd1g.fsf@rho.meyering.net> In-Reply-To: <7vzlw33a1o.fsf@gitster.siamese.dyndns.org> Junio C Hamano wrote: > Jim Meyering writes: > >>> While this change may be a prudent safeguard, there is something >>> else going on. Can you provide the callchain that led to the >>> parse_object_buffer() that gave SHA1 of a commit object with >>> type set to OBJ_TREE? Which caller does that bogus combination? >> >> Sure. >> Here's valgrind output from running this (from my reproducer): >> >> valgrind --trace-children=yes git clone . k >> --------------- >> error: Object 0d57588da39d10795486bd5451bc2660832228e6 is a commit, not a tree >> ==9483== Invalid read of size 1 >> ==9483== at 0x405C27: parse_object_buffer (object.c:146) >> ==9483== by 0x405CE4: parse_object (object.c:187) >> ==9483== by 0x403185: send_ref (upload-pack.c:561) >> ==9483== by 0x408EEF: do_for_each_ref (refs.c:546) >> ==9483== by 0x4036EC: main (upload-pack.c:587) > > Sorry, I asked for a wrong thing. parse_object() reads and > finds out the type, so type there is presumably the right type > of the object (which is OBJ_TREE). Then parse_object_buffer() > checks if it has already seen the object of the same SHA-1 and > finds that somebody had earlier told that SHA-1 name is of a > commit object. Either you found a SHA-1 collision (highly > unlikely) or the earlier caller had lied. And I think what > really needs to be fixed is that lying caller. That is not in > the above call chain. I haven't debugged it enough to find/fix the bug in parsecvs. I presume that parsecvs is the culprit, in constructing an invalid repository -- especially, since inserting the single missing tag into the ,v file is enough to make it so parsecvs creates a repository that no longer triggers the git bug.