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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 
clone: prevent clashing git dirs when cloning submodule in parallel
 
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>
1 parent b20c10f
Raw File
copy.c 
#include "cache.h"

int copy_fd(int ifd, int ofd)
{
	while (1) {
		char buffer[8192];
		ssize_t len = xread(ifd, buffer, sizeof(buffer));
		if (!len)
			break;
		if (len < 0)
			return COPY_READ_ERROR;
		if (write_in_full(ofd, buffer, len) < 0)
			return COPY_WRITE_ERROR;
	}
	return 0;
}

static int copy_times(const char *dst, const char *src)
{
	struct stat st;
	struct utimbuf times;
	if (stat(src, &st) < 0)
		return -1;
	times.actime = st.st_atime;
	times.modtime = st.st_mtime;
	if (utime(dst, &times) < 0)
		return -1;
	return 0;
}

int copy_file(const char *dst, const char *src, int mode)
{
	int fdi, fdo, status;

	mode = (mode & 0111) ? 0777 : 0666;
	if ((fdi = open(src, O_RDONLY)) < 0)
		return fdi;
	if ((fdo = open(dst, O_WRONLY | O_CREAT | O_EXCL, mode)) < 0) {
		close(fdi);
		return fdo;
	}
	status = copy_fd(fdi, fdo);
	switch (status) {
	case COPY_READ_ERROR:
		error_errno("copy-fd: read returned");
		break;
	case COPY_WRITE_ERROR:
		error_errno("copy-fd: write returned");
		break;
	}
	close(fdi);
	if (close(fdo) != 0)
		return error_errno("%s: close error", dst);

	if (!status && adjust_shared_perm(dst))
		return -1;

	return status;
}

int copy_file_with_time(const char *dst, const char *src, int mode)
{
	int status = copy_file(dst, src, mode);
	if (!status)
		return copy_times(dst, src);
	return status;
}
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