Revision 9cf85473209ea8ae2b56c13145c4704d12ee1374 authored by Filip Hejsek on 28 January 2024, 04:09:17 UTC, committed by Johannes Schindelin on 17 April 2024, 20:30:01 UTC
While it is expected to have several git dirs within the `.git/modules/` tree, it is important that they do not interfere with each other. For example, if one submodule was called "captain" and another submodule "captain/hooks", their respective git dirs would clash, as they would be located in `.git/modules/captain/` and `.git/modules/captain/hooks/`, respectively, i.e. the latter's files could clash with the actual Git hooks of the former. To prevent these clashes, and in particular to prevent hooks from being written and then executed as part of a recursive clone, we introduced checks as part of the fix for CVE-2019-1387 in a8dee3ca61 (Disallow dubiously-nested submodule git directories, 2019-10-01). It is currently possible to bypass the check for clashing submodule git dirs in two ways: 1. parallel cloning 2. checkout --recurse-submodules Let's check not only before, but also after parallel cloning (and before checking out the submodule), that the git dir is not clashing with another one, otherwise fail. This addresses the parallel cloning issue. As to the parallel checkout issue: It requires quite a few manual steps to create clashing git dirs because Git itself would refuse to initialize the inner one, as demonstrated by the test case. Nevertheless, let's teach the recursive checkout (namely, the `submodule_move_head()` function that is used by the recursive checkout) to be careful to verify that it does not use a clashing git dir, and if it does, disable it (by deleting the `HEAD` file so that subsequent Git calls won't recognize it as a git dir anymore). Note: The parallel cloning test case contains a `cat err` that proved to be highly useful when analyzing the racy nature of the operation (the operation can fail with three different error messages, depending on timing), and was left on purpose to ease future debugging should the need arise. Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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levenshtein.c
#include "cache.h"
#include "levenshtein.h"
/*
* This function implements the Damerau-Levenshtein algorithm to
* calculate a distance between strings.
*
* Basically, it says how many letters need to be swapped, substituted,
* deleted from, or added to string1, at least, to get string2.
*
* The idea is to build a distance matrix for the substrings of both
* strings. To avoid a large space complexity, only the last three rows
* are kept in memory (if swaps had the same or higher cost as one deletion
* plus one insertion, only two rows would be needed).
*
* At any stage, "i + 1" denotes the length of the current substring of
* string1 that the distance is calculated for.
*
* row2 holds the current row, row1 the previous row (i.e. for the substring
* of string1 of length "i"), and row0 the row before that.
*
* In other words, at the start of the big loop, row2[j + 1] contains the
* Damerau-Levenshtein distance between the substring of string1 of length
* "i" and the substring of string2 of length "j + 1".
*
* All the big loop does is determine the partial minimum-cost paths.
*
* It does so by calculating the costs of the path ending in characters
* i (in string1) and j (in string2), respectively, given that the last
* operation is a substitution, a swap, a deletion, or an insertion.
*
* This implementation allows the costs to be weighted:
*
* - w (as in "sWap")
* - s (as in "Substitution")
* - a (for insertion, AKA "Add")
* - d (as in "Deletion")
*
* Note that this algorithm calculates a distance _iff_ d == a.
*/
int levenshtein(const char *string1, const char *string2,
int w, int s, int a, int d)
{
int len1 = strlen(string1), len2 = strlen(string2);
int *row0, *row1, *row2;
int i, j;
ALLOC_ARRAY(row0, len2 + 1);
ALLOC_ARRAY(row1, len2 + 1);
ALLOC_ARRAY(row2, len2 + 1);
for (j = 0; j <= len2; j++)
row1[j] = j * a;
for (i = 0; i < len1; i++) {
int *dummy;
row2[0] = (i + 1) * d;
for (j = 0; j < len2; j++) {
/* substitution */
row2[j + 1] = row1[j] + s * (string1[i] != string2[j]);
/* swap */
if (i > 0 && j > 0 && string1[i - 1] == string2[j] &&
string1[i] == string2[j - 1] &&
row2[j + 1] > row0[j - 1] + w)
row2[j + 1] = row0[j - 1] + w;
/* deletion */
if (row2[j + 1] > row1[j + 1] + d)
row2[j + 1] = row1[j + 1] + d;
/* insertion */
if (row2[j + 1] > row2[j] + a)
row2[j + 1] = row2[j] + a;
}
dummy = row0;
row0 = row1;
row1 = row2;
row2 = dummy;
}
i = row1[len2];
free(row0);
free(row1);
free(row2);
return i;
}
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