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clone: prevent hooks from running during a clone

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Critical security issues typically combine relatively common
vulnerabilities such as case confusion in file paths with other
weaknesses in order to raise the severity of the attack.

One such weakness that has haunted the Git project in many a
submodule-related CVE is that any hooks that are found are executed
during a clone operation. Examples are the `post-checkout` and
`fsmonitor` hooks.

However, Git's design calls for hooks to be disabled by default, as only
disabled example hooks are copied over from the templates in
`<prefix>/share/git-core/templates/`.

As a defense-in-depth measure, let's prevent those hooks from running.

Obviously, administrators can choose to drop enabled hooks into the
template directory, though, _and_ it is also possible to override
`core.hooksPath`, in which case the new check needs to be disabled.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
This commit is contained in:
Johannes Schindelin
2024-03-28 19:21:06 +01:00
parent 584de0b4c2
commit 8db1e8743c
3 changed files with 94 additions and 1 deletions
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32
hook.c
View File

@ -3,6 +3,30 @@
#include "run-command.h"
#include "config.h"
static int identical_to_template_hook(const char *name, const char *path)
{
const char *env = getenv("GIT_CLONE_TEMPLATE_DIR");
const char *template_dir = get_template_dir(env && *env ? env : NULL);
struct strbuf template_path = STRBUF_INIT;
int found_template_hook, ret;
strbuf_addf(&template_path, "%s/hooks/%s", template_dir, name);
found_template_hook = access(template_path.buf, X_OK) >= 0;
#ifdef STRIP_EXTENSION
if (!found_template_hook) {
strbuf_addstr(&template_path, STRIP_EXTENSION);
found_template_hook = access(template_path.buf, X_OK) >= 0;
}
#endif
if (!found_template_hook)
return 0;
ret = do_files_match(template_path.buf, path);
strbuf_release(&template_path);
return ret;
}
const char *find_hook(const char *name)
{
static struct strbuf path = STRBUF_INIT;
@ -38,6 +62,14 @@ const char *find_hook(const char *name)
}
return NULL;
}
if (!git_hooks_path && git_env_bool("GIT_CLONE_PROTECTION_ACTIVE", 0) &&
!identical_to_template_hook(name, path.buf))
die(_("active `%s` hook found during `git clone`:\n\t%s\n"
"For security reasons, this is disallowed by default.\n"
"If this is intentional and the hook should actually "
"be run, please\nrun the command again with "
"`GIT_CLONE_PROTECTION_ACTIVE=false`"),
name, path.buf);
return path.buf;
}