After unpack_loose_header() returns, it will have inflated not only the
object header, but possibly some bytes of the object content. When we
call unpack_loose_rest() to extract the actual content, it finds those
extra bytes by skipping past the header's terminating NUL in the buffer.
Like this:
int bytes = strlen(buffer) + 1;
n = stream->total_out - bytes;
...
memcpy(buf, (char *) buffer + bytes, n);
This won't work with the OBJECT_INFO_ALLOW_UNKNOWN_TYPE flag, as there
we allow a header of arbitrary size. We put into a strbuf, but feed only
the final 32-byte chunk we read to unpack_loose_rest(). In that case
stream->total_out may unexpectedly large, and thus our "n" will be
large, causing an out-of-bounds read (we do check it against our
allocated buffer size, which prevents an out-of-bounds write).
Probably this could be made to work by feeding the strbuf to
unpack_loose_rest(), along with adjusting some types (e.g., "bytes"
would need to be a size_t, since it is no longer operating on a 32-byte
buffer).
But I don't think it's possible to actually trigger this in practice.
The only caller who passes ALLOW_UNKNOWN_TYPE is cat-file, which only
allows it with the "-t" and "-s" options (neither of which access the
content). There is one way you can _almost_ trigger it: the oid compat
routines (i.e., accessing sha1 via sha256 names and vice versa) will
convert objects on the fly (which requires access to the content) using
the same flags that were passed in. So in theory this:
t='some very large type field that causes an extra inflate call'
sha1_oid=$(git hash-object -w -t "$t" file)
sha256_oid=$(git rev-parse --output-object-format=sha256 $sha1_oid)
git cat-file --allow-unknown-type -s $sha256_oid
would try to access the content. But it doesn't work, because using
compat objects requires an entry in the .git/objects/loose-object-idx
file, and we don't generate such an entry for non-standard types (see
the "compat" section of write_object_file_literally()).
If we use "t=blob" instead, then it does access the compat object, but
it doesn't trigger the problem (because "blob" is a standard short type
name, and it fits in the initial 32-byte buffer).
So given that this is almost a memory error bug, I think it's worth
addressing. But because we can't actually trigger the situation, I'm
hesitant to try a fix that we can't run. Instead let's document the
restriction and protect ourselves from the out-of-bounds read by adding
a BUG() check.
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-<commandname>.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).
Those wishing to help with error message, usage and informational message
string translations (localization l10) should see po/README.md
(a po file is a Portable Object file that holds the translations).
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
