6c003d6ffb
We provide a reopen_tempfile() function, which is in turn
used by reopen_lockfile(). The idea is that a caller may
want to rewrite the tempfile without letting go of the lock.
And that's what our one caller does: after running
add--interactive, "commit -p" will update the cache-tree
extension of the index and write out the result, all while
holding the lock.
However, because we open the file with only the O_WRONLY
flag, the existing index content is left in place, and we
overwrite it starting at position 0. If the new index after
updating the cache-tree is smaller than the original, those
final bytes are not overwritten and remain in the file. This
results in a corrupt index, since those cruft bytes are
interpreted as part of the trailing hash (or even as an
extension, if there are enough bytes).
This bug actually pre-dates reopen_tempfile(); the original
code from 9c4d6c0297 (cache-tree: Write updated cache-tree
after commit, 2014-07-13) has the same bug, and those lines
were eventually refactored into the tempfile module. Nobody
noticed until now for two reasons:
- the bug can only be triggered in interactive mode
("commit -p" or "commit -i")
- the size of the index must shrink after updating the
cache-tree, which implies a non-trivial deletion. Notice
that the included test actually has to create a 2-deep
hierarchy. A single level is not enough to actually cause
shrinkage.
The fix is to truncate the file before writing out the
second index. We can do that at the caller by using
ftruncate(). But we shouldn't have to do that. There is no
other place in Git where we want to open a file and
overwrite bytes, making reopen_tempfile() a confusing and
error-prone interface. Let's pass O_TRUNC there, which gives
callers the same state they had after initially opening the
file or lock.
It's possible that we could later add a caller that wants
something else (e.g., to open with O_APPEND). But this is
the only caller we've had in the history of the codebase.
Let's punt on doing anything more clever until another one
comes along.
Reported-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
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