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Merge branch 'ownership-checks-in-local-clones'

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This topic addresses two CVEs:

- CVE-2024-32020:

  Local clones may end up hardlinking files into the target repository's
  object database when source and target repository reside on the same
  disk. If the source repository is owned by a different user, then
  those hardlinked files may be rewritten at any point in time by the
  untrusted user.

- CVE-2024-32021:

  When cloning a local source repository that contains symlinks via the
  filesystem, Git may create hardlinks to arbitrary user-readable files
  on the same filesystem as the target repository in the objects/
  directory.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
This commit is contained in:
Johannes Schindelin 2024-04-13 00:28:19 +02:00
parent 2b3d38a6b1 1204e1a824
commit 9e65df5eab
2 changed files with 58 additions and 5 deletions
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39
builtin/clone.c
View file

@ -320,7 +320,20 @@ static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
int src_len, dest_len;
struct dir_iterator *iter;
int iter_status;
struct strbuf realpath = STRBUF_INIT;
/*
* Refuse copying directories by default which aren't owned by us. The
* code that performs either the copying or hardlinking is not prepared
* to handle various edge cases where an adversary may for example
* racily swap out files for symlinks. This can cause us to
* inadvertently use the wrong source file.
*
* Furthermore, even if we were prepared to handle such races safely,
* creating hardlinks across user boundaries is an inherently unsafe
* operation as the hardlinked files can be rewritten at will by the
* potentially-untrusted user. We thus refuse to do so by default.
*/
die_upon_dubious_ownership(NULL, NULL, src_repo);
mkdir_if_missing(dest->buf, 0777);
@ -358,9 +371,27 @@ static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
if (unlink(dest->buf) && errno != ENOENT)
die_errno(_("failed to unlink '%s'"), dest->buf);
if (!option_no_hardlinks) {
strbuf_realpath(&realpath, src->buf, 1);
if (!link(realpath.buf, dest->buf))
if (!link(src->buf, dest->buf)) {
struct stat st;
/*
* Sanity-check whether the created hardlink
* actually links to the expected file now. This
* catches time-of-check-time-of-use bugs in
* case the source file was meanwhile swapped.
*/
if (lstat(dest->buf, &st))
die(_("hardlink cannot be checked at '%s'"), dest->buf);
if (st.st_mode != iter->st.st_mode ||
st.st_ino != iter->st.st_ino ||
st.st_dev != iter->st.st_dev ||
st.st_size != iter->st.st_size ||
st.st_uid != iter->st.st_uid ||
st.st_gid != iter->st.st_gid)
die(_("hardlink different from source at '%s'"), dest->buf);
continue;
}
if (option_local > 0)
die_errno(_("failed to create link '%s'"), dest->buf);
option_no_hardlinks = 1;
@ -373,8 +404,6 @@ static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
strbuf_setlen(src, src_len);
die(_("failed to iterate over '%s'"), src->buf);
}
strbuf_release(&realpath);
}
static void clone_local(const char *src_repo, const char *dest_repo)

24
t/t0033-safe-directory.sh
View file

@ -80,4 +80,28 @@ test_expect_success 'safe.directory in included file' '
git status
'
test_expect_success 'local clone of unowned repo refused in unsafe directory' '
test_when_finished "rm -rf source" &&
git init source &&
(
sane_unset GIT_TEST_ASSUME_DIFFERENT_OWNER &&
test_commit -C source initial
) &&
test_must_fail git clone --local source target &&
test_path_is_missing target
'
test_expect_success 'local clone of unowned repo accepted in safe directory' '
test_when_finished "rm -rf source" &&
git init source &&
(
sane_unset GIT_TEST_ASSUME_DIFFERENT_OWNER &&
test_commit -C source initial
) &&
test_must_fail git clone --local source target &&
git config --global --add safe.directory "$(pwd)/source/.git" &&
git clone --local source target &&
test_path_is_dir target
'
test_done