From bd6d72625f53e5983256da0ed7fe1a6431b3cfdf Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Fri, 17 May 2024 23:48:41 +0200 Subject: [PATCH] hooks(clone protections): simplify templates hooks validation When an active hook is encountered during a clone operation, to protect against Remote Code Execution attack vectors, Git checks whether the hook was copied over from the templates directory. When that logic was introduced, there was no other way to check this than to add a function to compare files. In the meantime, we've added code to compute the SHA-256 checksum of a given hook and compare that checksum against a list of known-safe ones. Let's simplify the logic by adding to said list when copying the templates' hooks. We need to be careful to support multi-process operations such as recursive submodule clones: In such a scenario, the list of SHA-256 checksums that is kept in memory is not enough, we also have to pass the information down to child processes via `GIT_CONFIG_PARAMETERS`. Extend the regression test in t5601 to ensure that recursive clones are handled as expected. Note: Technically there is no way that the checksums computed while initializing the submodules' gitdirs can be passed to the process that performs the checkout: For historical reasons, these operations are performed in processes spawned in separate loops from the super-project's `git clone` process. But since the templates from which the submodules are initialized are the very same as the ones from which the super-project is initialized, we can get away with using the list of SHA-256 checksums that is computed when initializing the super-project and passing that down to the `submodule--helper` processes that perform the recursive checkout. Signed-off-by: Johannes Schindelin --- builtin/init-db.c | 7 +++++++ hook.c | 43 ++++++++++++++++--------------------------- hook.h | 10 ++++++++++ setup.c | 1 + t/t5601-clone.sh | 19 +++++++++++++++++++ 5 files changed, 53 insertions(+), 27 deletions(-) diff --git a/builtin/init-db.c b/builtin/init-db.c index a101e7f94c119b..64357fdada4126 100644 --- a/builtin/init-db.c +++ b/builtin/init-db.c @@ -10,6 +10,8 @@ #include "exec-cmd.h" #include "parse-options.h" #include "worktree.h" +#include "run-command.h" +#include "hook.h" #ifdef NO_TRUSTABLE_FILEMODE #define TEST_FILEMODE 0 @@ -28,6 +30,7 @@ static void copy_templates_1(struct strbuf *path, struct strbuf *template_path, size_t path_baselen = path->len; size_t template_baselen = template_path->len; struct dirent *de; + int is_hooks_dir = ends_with(template_path->buf, "/hooks/"); /* Note: if ".git/hooks" file exists in the repository being * re-initialized, /etc/core-git/templates/hooks/update would @@ -80,6 +83,10 @@ static void copy_templates_1(struct strbuf *path, struct strbuf *template_path, strbuf_release(&lnk); } else if (S_ISREG(st_template.st_mode)) { + if (is_hooks_dir && + is_executable(template_path->buf)) + add_safe_hook(template_path->buf); + if (copy_file(path->buf, template_path->buf, st_template.st_mode)) die_errno(_("cannot copy '%s' to '%s'"), template_path->buf, path->buf); diff --git a/hook.c b/hook.c index f81b13df142f1a..9e762cc9af6371 100644 --- a/hook.c +++ b/hook.c @@ -4,32 +4,6 @@ #include "config.h" #include "strmap.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) { - strbuf_release(&template_path); - return 0; - } - - ret = do_files_match(template_path.buf, path); - - strbuf_release(&template_path); - return ret; -} - static struct strset safe_hook_sha256s = STRSET_INIT; static int safe_hook_sha256s_initialized; @@ -60,6 +34,22 @@ static int get_sha256_of_file_contents(const char *path, char *sha256) return 0; } +void add_safe_hook(const char *path) +{ + char sha256[GIT_SHA256_HEXSZ + 1] = { '\0' }; + + if (!get_sha256_of_file_contents(path, sha256)) { + char *p; + + strset_add(&safe_hook_sha256s, sha256); + + /* support multi-process operations e.g. recursive clones */ + p = xstrfmt("safe.hook.sha256=%s", sha256); + git_config_push_parameter(p); + free(p); + } +} + static int safe_hook_cb(const char *key, const char *value, void *d) { struct strset *set = d; @@ -131,7 +121,6 @@ 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) && !is_hook_safe_during_clone(name, path.buf, sha256)) die(_("active `%s` hook found during `git clone`:\n\t%s\n" "For security reasons, this is disallowed by default.\n" diff --git a/hook.h b/hook.h index 4258b13da0d7c3..e2034ee8b233a9 100644 --- a/hook.h +++ b/hook.h @@ -82,4 +82,14 @@ int run_hooks(const char *hook_name); * hook. This function behaves like the old run_hook_le() API. */ int run_hooks_l(const char *hook_name, ...); + +/** + * Mark the contents of the provided path as safe to run during a clone + * operation. + * + * This function is mainly used when copying templates to mark the + * just-copied hooks as benign. + */ +void add_safe_hook(const char *path); + #endif diff --git a/setup.c b/setup.c index c3301f5ab824b5..7f7538c9bf7688 100644 --- a/setup.c +++ b/setup.c @@ -7,6 +7,7 @@ #include "promisor-remote.h" #include "quote.h" #include "exec-cmd.h" +#include "hook.h" static int inside_git_dir = -1; static int inside_work_tree = -1; diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh index 20deca0231b8bf..71eaa3d1e14068 100755 --- a/t/t5601-clone.sh +++ b/t/t5601-clone.sh @@ -819,6 +819,25 @@ test_expect_success 'clone with init.templatedir runs hooks' ' git config --unset init.templateDir && ! grep "active .* hook found" err && test_path_is_missing hook-run-local-config/hook.run + ) && + + test_config_global protocol.file.allow always && + git -C tmpl/hooks submodule add "$(pwd)/tmpl/hooks" sub && + test_tick && + git -C tmpl/hooks add .gitmodules sub && + git -C tmpl/hooks commit -m submodule && + + ( + sane_unset GIT_TEMPLATE_DIR && + NO_SET_GIT_TEMPLATE_DIR=t && + export NO_SET_GIT_TEMPLATE_DIR && + + git -c init.templateDir="$(pwd)/tmpl" \ + clone --recurse-submodules \ + tmpl/hooks hook-run-submodule 2>err && + ! grep "active .* hook found" err && + test_path_is_file hook-run-submodule/hook.run && + test_path_is_file hook-run-submodule/sub/hook.run ) '