Revision e7cb0b4455c85b53aeba40f88ffddcf6d4002498 authored by Johannes Schindelin on 11 May 2018, 14:03:54 UTC, committed by Jeff King on 22 May 2018, 03:50:11 UTC
When we started to catch NTFS short names that clash with .git, we only
looked for GIT~1. This is sufficient because we only ever clone into an
empty directory, so .git is guaranteed to be the first subdirectory or
file in that directory.

However, even with a fresh clone, .gitmodules is *not* necessarily the
first file to be written that would want the NTFS short name GITMOD~1: a
malicious repository can add .gitmodul0000 and friends, which sorts
before `.gitmodules` and is therefore checked out *first*. For that
reason, we have to test not only for ~1 short names, but for others,
too.

It's hard to just adapt the existing checks in is_ntfs_dotgit(): since
Windows 2000 (i.e., in all Windows versions still supported by Git),
NTFS short names are only generated in the <prefix>~<number> form up to
number 4. After that, a *different* prefix is used, calculated from the
long file name using an undocumented, but stable algorithm.

For example, the short name of .gitmodules would be GITMOD~1, but if it
is taken, and all of ~2, ~3 and ~4 are taken, too, the short name
GI7EBA~1 will be used. From there, collisions are handled by
incrementing the number, shortening the prefix as needed (until ~9999999
is reached, in which case NTFS will not allow the file to be created).

We'd also want to handle .gitignore and .gitattributes, which suffer
from a similar problem, using the fall-back short names GI250A~1 and
GI7D29~1, respectively.

To accommodate for that, we could reimplement the hashing algorithm, but
it is just safer and simpler to provide the known prefixes. This
algorithm has been reverse-engineered and described at
https://usn.pw/blog/gen/2015/06/09/filenames/, which is defunct but
still available via https://web.archive.org/.

These can be recomputed by running the following Perl script:

-- snip --
use warnings;
use strict;

sub compute_short_name_hash ($) {
        my $checksum = 0;
        foreach (split('', $_[0])) {
                $checksum = ($checksum * 0x25 + ord($_)) & 0xffff;
        }

        $checksum = ($checksum * 314159269) & 0xffffffff;
        $checksum = 1 + (~$checksum & 0x7fffffff) if ($checksum & 0x80000000);
        $checksum -= (($checksum * 1152921497) >> 60) * 1000000007;

        return scalar reverse sprintf("%x", $checksum & 0xffff);
}

print compute_short_name_hash($ARGV[0]);
-- snap --

E.g., running that with the argument ".gitignore" will
result in "250a" (which then becomes "gi250a" in the code).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Jeff King <peff@peff.net>
1 parent 0fc333b
Raw File
column.h
#ifndef COLUMN_H
#define COLUMN_H

#define COL_LAYOUT_MASK   0x000F
#define COL_ENABLE_MASK   0x0030   /* always, never or auto */
#define COL_PARSEOPT      0x0040   /* --column is given from cmdline */
#define COL_DENSE         0x0080   /* Shrink columns when possible,
				      making space for more columns */

#define COL_DISABLED      0x0000   /* must be zero */
#define COL_ENABLED       0x0010
#define COL_AUTO          0x0020

#define COL_LAYOUT(c) ((c) & COL_LAYOUT_MASK)
#define COL_COLUMN             0   /* Fill columns before rows */
#define COL_ROW                1   /* Fill rows before columns */
#define COL_PLAIN             15   /* one column */

#define explicitly_enable_column(c) \
	(((c) & COL_PARSEOPT) && column_active(c))

struct column_options {
	int width;
	int padding;
	const char *indent;
	const char *nl;
};

struct option;
extern int parseopt_column_callback(const struct option *, const char *, int);
extern int git_column_config(const char *var, const char *value,
			     const char *command, unsigned int *colopts);
extern int finalize_colopts(unsigned int *colopts, int stdout_is_tty);
static inline int column_active(unsigned int colopts)
{
	return (colopts & COL_ENABLE_MASK) == COL_ENABLED;
}

extern void print_columns(const struct string_list *list, unsigned int colopts,
			  const struct column_options *opts);

extern int run_column_filter(int colopts, const struct column_options *);
extern int stop_column_filter(void);

#endif
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