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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diffcore-delta.c
#include "cache.h"
#include "diff.h"
#include "diffcore.h"
/*
* Idea here is very simple.
*
* Almost all data we are interested in are text, but sometimes we have
* to deal with binary data. So we cut them into chunks delimited by
* LF byte, or 64-byte sequence, whichever comes first, and hash them.
*
* For those chunks, if the source buffer has more instances of it
* than the destination buffer, that means the difference are the
* number of bytes not copied from source to destination. If the
* counts are the same, everything was copied from source to
* destination. If the destination has more, everything was copied,
* and destination added more.
*
* We are doing an approximation so we do not really have to waste
* memory by actually storing the sequence. We just hash them into
* somewhere around 2^16 hashbuckets and count the occurrences.
*/
/* Wild guess at the initial hash size */
#define INITIAL_HASH_SIZE 9
/* We leave more room in smaller hash but do not let it
* grow to have unused hole too much.
*/
#define INITIAL_FREE(sz_log2) ((1<<(sz_log2))*(sz_log2-3)/(sz_log2))
/* A prime rather carefully chosen between 2^16..2^17, so that
* HASHBASE < INITIAL_FREE(17). We want to keep the maximum hashtable
* size under the current 2<<17 maximum, which can hold this many
* different values before overflowing to hashtable of size 2<<18.
*/
#define HASHBASE 107927
struct spanhash {
unsigned int hashval;
unsigned int cnt;
};
struct spanhash_top {
int alloc_log2;
int free;
struct spanhash data[FLEX_ARRAY];
};
static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig)
{
struct spanhash_top *new_spanhash;
int i;
int osz = 1 << orig->alloc_log2;
int sz = osz << 1;
new_spanhash = xmalloc(st_add(sizeof(*orig),
st_mult(sizeof(struct spanhash), sz)));
new_spanhash->alloc_log2 = orig->alloc_log2 + 1;
new_spanhash->free = INITIAL_FREE(new_spanhash->alloc_log2);
memset(new_spanhash->data, 0, sizeof(struct spanhash) * sz);
for (i = 0; i < osz; i++) {
struct spanhash *o = &(orig->data[i]);
int bucket;
if (!o->cnt)
continue;
bucket = o->hashval & (sz - 1);
while (1) {
struct spanhash *h = &(new_spanhash->data[bucket++]);
if (!h->cnt) {
h->hashval = o->hashval;
h->cnt = o->cnt;
new_spanhash->free--;
break;
}
if (sz <= bucket)
bucket = 0;
}
}
free(orig);
return new_spanhash;
}
static struct spanhash_top *add_spanhash(struct spanhash_top *top,
unsigned int hashval, int cnt)
{
int bucket, lim;
struct spanhash *h;
lim = (1 << top->alloc_log2);
bucket = hashval & (lim - 1);
while (1) {
h = &(top->data[bucket++]);
if (!h->cnt) {
h->hashval = hashval;
h->cnt = cnt;
top->free--;
if (top->free < 0)
return spanhash_rehash(top);
return top;
}
if (h->hashval == hashval) {
h->cnt += cnt;
return top;
}
if (lim <= bucket)
bucket = 0;
}
}
static int spanhash_cmp(const void *a_, const void *b_)
{
const struct spanhash *a = a_;
const struct spanhash *b = b_;
/* A count of zero compares at the end.. */
if (!a->cnt)
return !b->cnt ? 0 : 1;
if (!b->cnt)
return -1;
return a->hashval < b->hashval ? -1 :
a->hashval > b->hashval ? 1 : 0;
}
static struct spanhash_top *hash_chars(struct repository *r,
struct diff_filespec *one)
{
int i, n;
unsigned int accum1, accum2, hashval;
struct spanhash_top *hash;
unsigned char *buf = one->data;
unsigned int sz = one->size;
int is_text = !diff_filespec_is_binary(r, one);
i = INITIAL_HASH_SIZE;
hash = xmalloc(st_add(sizeof(*hash),
st_mult(sizeof(struct spanhash), (size_t)1 << i)));
hash->alloc_log2 = i;
hash->free = INITIAL_FREE(i);
memset(hash->data, 0, sizeof(struct spanhash) * ((size_t)1 << i));
n = 0;
accum1 = accum2 = 0;
while (sz) {
unsigned int c = *buf++;
unsigned int old_1 = accum1;
sz--;
/* Ignore CR in CRLF sequence if text */
if (is_text && c == '\r' && sz && *buf == '\n')
continue;
accum1 = (accum1 << 7) ^ (accum2 >> 25);
accum2 = (accum2 << 7) ^ (old_1 >> 25);
accum1 += c;
if (++n < 64 && c != '\n')
continue;
hashval = (accum1 + accum2 * 0x61) % HASHBASE;
hash = add_spanhash(hash, hashval, n);
n = 0;
accum1 = accum2 = 0;
}
QSORT(hash->data, (size_t)1ul << hash->alloc_log2, spanhash_cmp);
return hash;
}
int diffcore_count_changes(struct repository *r,
struct diff_filespec *src,
struct diff_filespec *dst,
void **src_count_p,
void **dst_count_p,
unsigned long *src_copied,
unsigned long *literal_added)
{
struct spanhash *s, *d;
struct spanhash_top *src_count, *dst_count;
unsigned long sc, la;
src_count = dst_count = NULL;
if (src_count_p)
src_count = *src_count_p;
if (!src_count) {
src_count = hash_chars(r, src);
if (src_count_p)
*src_count_p = src_count;
}
if (dst_count_p)
dst_count = *dst_count_p;
if (!dst_count) {
dst_count = hash_chars(r, dst);
if (dst_count_p)
*dst_count_p = dst_count;
}
sc = la = 0;
s = src_count->data;
d = dst_count->data;
for (;;) {
unsigned dst_cnt, src_cnt;
if (!s->cnt)
break; /* we checked all in src */
while (d->cnt) {
if (d->hashval >= s->hashval)
break;
la += d->cnt;
d++;
}
src_cnt = s->cnt;
dst_cnt = 0;
if (d->cnt && d->hashval == s->hashval) {
dst_cnt = d->cnt;
d++;
}
if (src_cnt < dst_cnt) {
la += dst_cnt - src_cnt;
sc += src_cnt;
}
else
sc += dst_cnt;
s++;
}
while (d->cnt) {
la += d->cnt;
d++;
}
if (!src_count_p)
free(src_count);
if (!dst_count_p)
free(dst_count);
*src_copied = sc;
*literal_added = la;
return 0;
}
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