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The resolve_ref_unsafe() function can, and sometimes will in the case of this codepath, return the char * passed to it to the caller. In this case we construct a strbuf, free it, and then continue using the dst_name after that free(). The code being fixed dates back toda3efdb17b("receive-pack: detect aliased updates which can occur with symrefs", 2010-04-19). When it was originally added it didn't have this bug, it was introduced when it was subsequently modified to use strbuf in6b01ecfe22("ref namespaces: Support remote repositories via upload-pack and receive-pack", 2011-07-08). This is theoretically a security issue, the C standard makes no guarantees that a value you use after free() hasn't been poked at or changed by something else on the system, but in practice modern OSs will have mapped the relevant page to this process, so nothing else would have used it. We do no further allocations between the free() and use-after-free, so we ourselves didn't corrupt or change the value. Jeff investigated that and found: "It probably would be an issue if the allocation were larger. glibc at least will use mmap()/munmap() after some cutoff[1], in which case we'd get a segfault from hitting the unmapped page. But for small allocations, it just bumps brk() and the memory is still available for further allocations after free(). [...] If you had a sufficiently large refname you might be able to trigger the bug [...]. I tried to push such a ref. I had to manually make a packed-refs file with the long name to avoid filesystem limits (though probably you could have a long a/b/c/ name on ext4). But the result can't actually be pushed, because it all has to fit into a 64k pkt-line as part of the push protocol.". An a alternative and more succinct way of implementing this would have been to do the strbuf_release() at the end of check_aliased_update() and use "goto out" instead of the early "return" statements. Hopefully this approach of using a helper instead makes it easier to follow. 1. Jeff: "Weirdly, the mmap() cutoff on my glibc system is 135168 bytes. Which is...2^17 + 2^12? 33 pages? I'm sure there's a good reason for that, but I didn't dig into it." Reported-by: 王健强 <jianqiang.wang@securitygossip.com> Helped-by: Jeff King <peff@peff.net> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial or git help tutorial, and the
documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.txt
(man gitcvs-migration or git help cvs-migration if git is
installed).
The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission). To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org. The mailing list archives are available at https://public-inbox.org/git/, http://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):
- random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
- "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks