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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lockfile.c
/*
* Copyright (c) 2005, Junio C Hamano
*/
#include "cache.h"
#include "lockfile.h"
/*
* path = absolute or relative path name
*
* Remove the last path name element from path (leaving the preceding
* "/", if any). If path is empty or the root directory ("/"), set
* path to the empty string.
*/
static void trim_last_path_component(struct strbuf *path)
{
int i = path->len;
/* back up past trailing slashes, if any */
while (i && path->buf[i - 1] == '/')
i--;
/*
* then go backwards until a slash, or the beginning of the
* string
*/
while (i && path->buf[i - 1] != '/')
i--;
strbuf_setlen(path, i);
}
/* We allow "recursive" symbolic links. Only within reason, though */
#define MAXDEPTH 5
/*
* path contains a path that might be a symlink.
*
* If path is a symlink, attempt to overwrite it with a path to the
* real file or directory (which may or may not exist), following a
* chain of symlinks if necessary. Otherwise, leave path unmodified.
*
* This is a best-effort routine. If an error occurs, path will
* either be left unmodified or will name a different symlink in a
* symlink chain that started with the original path.
*/
static void resolve_symlink(struct strbuf *path)
{
int depth = MAXDEPTH;
static struct strbuf link = STRBUF_INIT;
while (depth--) {
if (strbuf_readlink(&link, path->buf, path->len) < 0)
break;
if (is_absolute_path(link.buf))
/* absolute path simply replaces p */
strbuf_reset(path);
else
/*
* link is a relative path, so replace the
* last element of p with it.
*/
trim_last_path_component(path);
strbuf_addbuf(path, &link);
}
strbuf_reset(&link);
}
/* Make sure errno contains a meaningful value on error */
static int lock_file(struct lock_file *lk, const char *path, int flags,
int mode)
{
struct strbuf filename = STRBUF_INIT;
strbuf_addstr(&filename, path);
if (!(flags & LOCK_NO_DEREF))
resolve_symlink(&filename);
strbuf_addstr(&filename, LOCK_SUFFIX);
lk->tempfile = create_tempfile_mode(filename.buf, mode);
strbuf_release(&filename);
return lk->tempfile ? lk->tempfile->fd : -1;
}
/*
* Constants defining the gaps between attempts to lock a file. The
* first backoff period is approximately INITIAL_BACKOFF_MS
* milliseconds. The longest backoff period is approximately
* (BACKOFF_MAX_MULTIPLIER * INITIAL_BACKOFF_MS) milliseconds.
*/
#define INITIAL_BACKOFF_MS 1L
#define BACKOFF_MAX_MULTIPLIER 1000
/*
* Try locking path, retrying with quadratic backoff for at least
* timeout_ms milliseconds. If timeout_ms is 0, try locking the file
* exactly once. If timeout_ms is -1, try indefinitely.
*/
static int lock_file_timeout(struct lock_file *lk, const char *path,
int flags, long timeout_ms, int mode)
{
int n = 1;
int multiplier = 1;
long remaining_ms = 0;
static int random_initialized = 0;
if (timeout_ms == 0)
return lock_file(lk, path, flags, mode);
if (!random_initialized) {
srand((unsigned int)getpid());
random_initialized = 1;
}
if (timeout_ms > 0)
remaining_ms = timeout_ms;
while (1) {
long backoff_ms, wait_ms;
int fd;
fd = lock_file(lk, path, flags, mode);
if (fd >= 0)
return fd; /* success */
else if (errno != EEXIST)
return -1; /* failure other than lock held */
else if (timeout_ms > 0 && remaining_ms <= 0)
return -1; /* failure due to timeout */
backoff_ms = multiplier * INITIAL_BACKOFF_MS;
/* back off for between 0.75*backoff_ms and 1.25*backoff_ms */
wait_ms = (750 + rand() % 500) * backoff_ms / 1000;
sleep_millisec(wait_ms);
remaining_ms -= wait_ms;
/* Recursion: (n+1)^2 = n^2 + 2n + 1 */
multiplier += 2*n + 1;
if (multiplier > BACKOFF_MAX_MULTIPLIER)
multiplier = BACKOFF_MAX_MULTIPLIER;
else
n++;
}
}
void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
{
if (err == EEXIST) {
strbuf_addf(buf, _("Unable to create '%s.lock': %s.\n\n"
"Another git process seems to be running in this repository, e.g.\n"
"an editor opened by 'git commit'. Please make sure all processes\n"
"are terminated then try again. If it still fails, a git process\n"
"may have crashed in this repository earlier:\n"
"remove the file manually to continue."),
absolute_path(path), strerror(err));
} else
strbuf_addf(buf, _("Unable to create '%s.lock': %s"),
absolute_path(path), strerror(err));
}
NORETURN void unable_to_lock_die(const char *path, int err)
{
struct strbuf buf = STRBUF_INIT;
unable_to_lock_message(path, err, &buf);
die("%s", buf.buf);
}
/* This should return a meaningful errno on failure */
int hold_lock_file_for_update_timeout_mode(struct lock_file *lk,
const char *path, int flags,
long timeout_ms, int mode)
{
int fd = lock_file_timeout(lk, path, flags, timeout_ms, mode);
if (fd < 0) {
if (flags & LOCK_DIE_ON_ERROR)
unable_to_lock_die(path, errno);
if (flags & LOCK_REPORT_ON_ERROR) {
struct strbuf buf = STRBUF_INIT;
unable_to_lock_message(path, errno, &buf);
error("%s", buf.buf);
strbuf_release(&buf);
}
}
return fd;
}
char *get_locked_file_path(struct lock_file *lk)
{
struct strbuf ret = STRBUF_INIT;
strbuf_addstr(&ret, get_tempfile_path(lk->tempfile));
if (ret.len <= LOCK_SUFFIX_LEN ||
strcmp(ret.buf + ret.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
BUG("get_locked_file_path() called for malformed lock object");
/* remove ".lock": */
strbuf_setlen(&ret, ret.len - LOCK_SUFFIX_LEN);
return strbuf_detach(&ret, NULL);
}
int commit_lock_file(struct lock_file *lk)
{
char *result_path = get_locked_file_path(lk);
if (commit_lock_file_to(lk, result_path)) {
int save_errno = errno;
free(result_path);
errno = save_errno;
return -1;
}
free(result_path);
return 0;
}
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