Hi Carlo
On 05/05/2022 01:50, Carlo Marcelo Arenas Belón wrote:
8959555cee7 (setup_git_directory(): add an owner check for the top-level
directory, 2022-03-02), adds a function to check for ownership of
repositories using a directory that is representative of it (its workdir)
and ways to add it to an exception list if needed, but that check breaks
when the ownership of the workdir is not the same than the ownership of
directory where the configuration and other relevant files reside.
An attacker could create a git repository in a directory that he has write
access to but is owned by the victim, and therefore workaround the fix that
was introduced with CVE-2022-24765 to attack them, like in the following
scenario which could result in privilege escalation if root then runs a git
command in that directory or any of its sub directories:
$ git -C /tmp init
To avoid that, extend the ensure_valid_ownership function to be able to
check for ownership of both the worktree and the gitdir, and use that for
non bare repositories.
Looking at the code below it now only ever checks the ownership of the
gitdir, it no longer checks the ownership of the worktree. I haven't
really thought through what happens if I cd into a worktree added by an
attacker to a repository that I own which has extentions.worktreeConfig
set. My initial thought is that if they can add a worktree then they can
probably edit the repository config anyway but I wonder if an attacker
can set GIT_COMMON_DIR to a directory where they have write permission
to add a worktree to a repository where they don't have write permission.
[...]
diff --git a/setup.c b/setup.c
index aad9ace0af9..0fae2d71a3c 100644
--- a/setup.c
+++ b/setup.c
@@ -1054,14 +1054,21 @@ static int safe_directory_cb(const char *key, const char *value, void *d)
return 0;
}
-static int ensure_valid_ownership(const char *path)
+static int ensure_valid_ownership(const char *worktree, const char *gitdir)
{
- struct safe_directory_data data = { .path = path };
+ struct safe_directory_data data = { .path = worktree };
We keep checking the worktree path against safe.directory - good.
+ const char *check_path;
+
+ if (gitdir)
+ check_path = gitdir;
+ else
+ check_path = worktree;
We check either the gitdir or worktree but always call this function
with a non-NULL gitdir so in fact always check that. This code could be
removed.
if (!git_env_bool("GIT_TEST_ASSUME_DIFFERENT_OWNER", 0) &&
- is_path_owned_by_current_user(path))
+ is_path_owned_by_current_user(check_path))
Previously we checked the ownership of the worktree but now we check the
ownership of the gitdir instead to handle the "git -C /tmp init" case.
return 1;
+ data.is_safe = 0; /* ensure we are initialized and secure by default */
read_very_early_config(safe_directory_cb, &data);
return data.is_safe;
@@ -1166,14 +1173,25 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
}
strbuf_setlen(dir, offset);
if (gitdirenv) {
- if (!ensure_valid_ownership(dir->buf))
+ const char *gitdir_to_check = gitdirenv;
+ struct strbuf gdbuf = STRBUF_INIT;
+ int ret;
+
+ if (!is_absolute_path(gitdirenv)) {
+ strbuf_addf(&gdbuf, "%s/%s", dir->buf,
+ gitdirenv);
+ gitdir_to_check = gdbuf.buf;
+ }
+ ret = ensure_valid_ownership(dir->buf, gitdir_to_check);
+ strbuf_release(&gdbuf);
+ if (!ret)
return GIT_DIR_INVALID_OWNERSHIP;
strbuf_addstr(gitdir, gitdirenv);
return GIT_DIR_DISCOVERED;
}
if (is_git_directory(dir->buf)) {
- if (!ensure_valid_ownership(dir->buf))
+ if (!ensure_valid_ownership(NULL, dir->buf))
Previously we checked bare repositories against safe.directory now we no
longer do that as worktree is NULL. If this is intentional it should be
flagged up in the commit message.
Best Wishes
Phillip
return GIT_DIR_INVALID_OWNERSHIP;
strbuf_addstr(gitdir, ".");
return GIT_DIR_BARE;
diff --git a/t/t0034-root-safe-directory.sh b/t/t0034-root-safe-directory.sh
index a68e1d7602b..a3ddebb009a 100755
--- a/t/t0034-root-safe-directory.sh
+++ b/t/t0034-root-safe-directory.sh
@@ -47,6 +47,35 @@ test_expect_success SUDO 'sudo git status as original owner' '
)
'
+test_expect_success SUDO 'unsecure worktree with non bare repository' '
+ sudo rm -rf root &&
+ sudo mkdir -p root/t &&
+ sudo chmod 1777 root/t &&
+ (
+ cd root/t &&
+ git init &&
+ git status &&
+ sudo git status &&
+ run_with_sudo <<-END
+ unset SUDO_UID &&
+ ! git status
+ END
+ )
+'
+
+test_expect_success SUDO 'non bare repository using a gitfile' '
+ sudo rm -rf root &&
+ mkdir -p root/w &&
+ mkdir -p root/e &&
+ (
+ cd root/w &&
+ git init --separate-git-dir ../e &&
+ git status &&
+ sudo chown -R root ../e &&
+ test_must_fail git status
+ )
+'
+
# this destroys the test environment used above
test_expect_success SUDO 'cleanup regression' '
sudo rm -rf root
