From 9f6e63b966e9876ca6f990819fabafc473a3c9b0 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?= Date: Mon, 7 Mar 2022 13:33:45 +0100 Subject: [PATCH 1/2] merge: don't run post-hook logic on --no-verify MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fix a minor bug introduced in bc40ce4de61 (merge: --no-verify to bypass pre-merge-commit hook, 2019-08-07), when that change made the --no-verify option bypass the "pre-merge-commit" hook it didn't update the corresponding find_hook() (later hook_exists()) condition. As can be seen in the preceding commit in 6098817fd7f (git-merge: honor pre-merge-commit hook, 2019-08-07) the two should go hand in hand. There's no point in invoking discard_cache() here if the hook couldn't have possibly updated the index. It's buggy that we use "hook_exist()" here, and as discussed in the subsequent commit it's subject to obscure race conditions that we're about to fix, but for now this change is a strict improvement that retains any caveats to do with the use of "hooks_exist()" as-is. Signed-off-by: Ævar Arnfjörð Bjarmason Signed-off-by: Junio C Hamano --- builtin/merge.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/builtin/merge.c b/builtin/merge.c index a94a03384a..b26b4c4515 100644 --- a/builtin/merge.c +++ b/builtin/merge.c @@ -845,15 +845,18 @@ static void prepare_to_commit(struct commit_list *remoteheads) struct strbuf msg = STRBUF_INIT; const char *index_file = get_index_file(); - if (!no_verify && run_commit_hook(0 < option_edit, index_file, "pre-merge-commit", NULL)) - abort_commit(remoteheads, NULL); - /* - * Re-read the index as pre-merge-commit hook could have updated it, - * and write it out as a tree. We must do this before we invoke - * the editor and after we invoke run_status above. - */ - if (hook_exists("pre-merge-commit")) - discard_cache(); + if (!no_verify) { + if (run_commit_hook(0 < option_edit, index_file, + "pre-merge-commit", NULL)) + abort_commit(remoteheads, NULL); + /* + * Re-read the index as pre-merge-commit hook could have updated it, + * and write it out as a tree. We must do this before we invoke + * the editor and after we invoke run_status above. + */ + if (hook_exists("pre-merge-commit")) + discard_cache(); + } read_cache_from(index_file); strbuf_addbuf(&msg, &merge_msg); if (squash) From a8cc594333848713b8e772cccf8159196ea85ede Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?= Date: Mon, 7 Mar 2022 13:33:46 +0100 Subject: [PATCH 2/2] hooks: fix an obscure TOCTOU "did we just run a hook?" race MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fix a Time-of-check to time-of-use (TOCTOU) race in code added in 680ee550d72 (commit: skip discarding the index if there is no pre-commit hook, 2017-08-14). This obscure race condition can occur if we e.g. ran the "pre-commit" hook and it modified the index, but hook_exists() returns false later on (e.g., because the hook itself went away, the directory became unreadable, etc.). Then we won't call discard_cache() when we should have. The race condition itself probably doesn't matter, and users would have been unlikely to run into it in practice. This problem has been noted on-list when 680ee550d72 was discussed[1], but had not been fixed. This change is mainly intended to improve the readability of the code involved, and to make reasoning about it more straightforward. It wasn't as obvious what we were trying to do here, but by having an "invoked_hook" it's clearer that e.g. our discard_cache() is happening because of the earlier hook execution. Let's also change this for the push-to-checkout hook. Now instead of checking if the hook exists and either doing a push to checkout or a push to deploy we'll always attempt a push to checkout. If the hook doesn't exist we'll fall back on push to deploy. The same behavior as before, without the TOCTOU race. See 0855331941b (receive-pack: support push-to-checkout hook, 2014-12-01) for the introduction of the previous behavior. This leaves uses of hook_exists() in two places that matter. The "reference-transaction" check in refs.c, see 67541597670 (refs: implement reference transaction hook, 2020-06-19), and the "prepare-commit-msg" hook, see 66618a50f9c (sequencer: run 'prepare-commit-msg' hook, 2018-01-24). In both of those cases we're saving ourselves CPU time by not preparing data for the hook that we'll then do nothing with if we don't have the hook. So using this "invoked_hook" pattern doesn't make sense in those cases. The "reference-transaction" and "prepare-commit-msg" hook also aren't racy. In those cases we'll skip the hook runs if we race with a new hook being added, whereas in the TOCTOU races being fixed here we were incorrectly skipping the required post-hook logic. 1. https://lore.kernel.org/git/20170810191613.kpmhzg4seyxy3cpq@sigill.intra.peff.net/ Signed-off-by: Ævar Arnfjörð Bjarmason Signed-off-by: Junio C Hamano --- builtin/commit.c | 18 +++++++++++------- builtin/merge.c | 11 +++++++---- builtin/receive-pack.c | 8 +++++--- commit.c | 2 +- commit.h | 3 ++- hook.c | 7 +++++++ hook.h | 12 ++++++++++++ sequencer.c | 4 ++-- 8 files changed, 47 insertions(+), 18 deletions(-) diff --git a/builtin/commit.c b/builtin/commit.c index 8b8bdad395..009a1de0a3 100644 --- a/builtin/commit.c +++ b/builtin/commit.c @@ -726,11 +726,13 @@ static int prepare_to_commit(const char *index_file, const char *prefix, int clean_message_contents = (cleanup_mode != COMMIT_MSG_CLEANUP_NONE); int old_display_comment_prefix; int merge_contains_scissors = 0; + int invoked_hook; /* This checks and barfs if author is badly specified */ determine_author_info(author_ident); - if (!no_verify && run_commit_hook(use_editor, index_file, "pre-commit", NULL)) + if (!no_verify && run_commit_hook(use_editor, index_file, &invoked_hook, + "pre-commit", NULL)) return 0; if (squash_message) { @@ -1053,10 +1055,10 @@ static int prepare_to_commit(const char *index_file, const char *prefix, return 0; } - if (!no_verify && hook_exists("pre-commit")) { + if (!no_verify && invoked_hook) { /* - * Re-read the index as pre-commit hook could have updated it, - * and write it out as a tree. We must do this before we invoke + * Re-read the index as the pre-commit-commit hook was invoked + * and could have updated it. We must do this before we invoke * the editor and after we invoke run_status above. */ discard_cache(); @@ -1068,7 +1070,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix, return 0; } - if (run_commit_hook(use_editor, index_file, "prepare-commit-msg", + if (run_commit_hook(use_editor, index_file, NULL, "prepare-commit-msg", git_path_commit_editmsg(), hook_arg1, hook_arg2, NULL)) return 0; @@ -1085,7 +1087,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix, } if (!no_verify && - run_commit_hook(use_editor, index_file, "commit-msg", git_path_commit_editmsg(), NULL)) { + run_commit_hook(use_editor, index_file, NULL, "commit-msg", + git_path_commit_editmsg(), NULL)) { return 0; } @@ -1841,7 +1844,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix) repo_rerere(the_repository, 0); run_auto_maintenance(quiet); - run_commit_hook(use_editor, get_index_file(), "post-commit", NULL); + run_commit_hook(use_editor, get_index_file(), NULL, "post-commit", + NULL); if (amend && !no_post_rewrite) { commit_post_rewrite(the_repository, current_head, &oid); } diff --git a/builtin/merge.c b/builtin/merge.c index b26b4c4515..f178f5a3ee 100644 --- a/builtin/merge.c +++ b/builtin/merge.c @@ -846,7 +846,9 @@ static void prepare_to_commit(struct commit_list *remoteheads) const char *index_file = get_index_file(); if (!no_verify) { - if (run_commit_hook(0 < option_edit, index_file, + int invoked_hook; + + if (run_commit_hook(0 < option_edit, index_file, &invoked_hook, "pre-merge-commit", NULL)) abort_commit(remoteheads, NULL); /* @@ -854,7 +856,7 @@ static void prepare_to_commit(struct commit_list *remoteheads) * and write it out as a tree. We must do this before we invoke * the editor and after we invoke run_status above. */ - if (hook_exists("pre-merge-commit")) + if (invoked_hook) discard_cache(); } read_cache_from(index_file); @@ -878,7 +880,8 @@ static void prepare_to_commit(struct commit_list *remoteheads) append_signoff(&msg, ignore_non_trailer(msg.buf, msg.len), 0); write_merge_heads(remoteheads); write_file_buf(git_path_merge_msg(the_repository), msg.buf, msg.len); - if (run_commit_hook(0 < option_edit, get_index_file(), "prepare-commit-msg", + if (run_commit_hook(0 < option_edit, get_index_file(), NULL, + "prepare-commit-msg", git_path_merge_msg(the_repository), "merge", NULL)) abort_commit(remoteheads, NULL); if (0 < option_edit) { @@ -887,7 +890,7 @@ static void prepare_to_commit(struct commit_list *remoteheads) } if (!no_verify && run_commit_hook(0 < option_edit, get_index_file(), - "commit-msg", + NULL, "commit-msg", git_path_merge_msg(the_repository), NULL)) abort_commit(remoteheads, NULL); diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c index d10aeb7e78..d4db577669 100644 --- a/builtin/receive-pack.c +++ b/builtin/receive-pack.c @@ -1408,10 +1408,12 @@ static const char *push_to_deploy(unsigned char *sha1, static const char *push_to_checkout_hook = "push-to-checkout"; static const char *push_to_checkout(unsigned char *hash, + int *invoked_hook, struct strvec *env, const char *work_tree) { struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT; + opt.invoked_hook = invoked_hook; strvec_pushf(env, "GIT_WORK_TREE=%s", absolute_path(work_tree)); strvec_pushv(&opt.env, env->v); @@ -1426,6 +1428,7 @@ static const char *update_worktree(unsigned char *sha1, const struct worktree *w { const char *retval, *git_dir; struct strvec env = STRVEC_INIT; + int invoked_hook; if (!worktree || !worktree->path) BUG("worktree->path must be non-NULL"); @@ -1436,10 +1439,9 @@ static const char *update_worktree(unsigned char *sha1, const struct worktree *w strvec_pushf(&env, "GIT_DIR=%s", absolute_path(git_dir)); - if (!hook_exists(push_to_checkout_hook)) + retval = push_to_checkout(sha1, &invoked_hook, &env, worktree->path); + if (!invoked_hook) retval = push_to_deploy(sha1, &env, worktree->path); - else - retval = push_to_checkout(sha1, &env, worktree->path); strvec_clear(&env); return retval; diff --git a/commit.c b/commit.c index d400f5dfa2..396e14d7b3 100644 --- a/commit.c +++ b/commit.c @@ -1713,7 +1713,7 @@ size_t ignore_non_trailer(const char *buf, size_t len) } int run_commit_hook(int editor_is_used, const char *index_file, - const char *name, ...) + int *invoked_hook, const char *name, ...) { struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT; va_list args; diff --git a/commit.h b/commit.h index 38cc542661..3b174135bc 100644 --- a/commit.h +++ b/commit.h @@ -369,7 +369,8 @@ int compare_commits_by_commit_date(const void *a_, const void *b_, void *unused) int compare_commits_by_gen_then_commit_date(const void *a_, const void *b_, void *unused); LAST_ARG_MUST_BE_NULL -int run_commit_hook(int editor_is_used, const char *index_file, const char *name, ...); +int run_commit_hook(int editor_is_used, const char *index_file, + int *invoked_hook, const char *name, ...); /* Sign a commit or tag buffer, storing the result in a header. */ int sign_with_header(struct strbuf *buf, const char *keyid); diff --git a/hook.c b/hook.c index 69a215b2c3..1d51be3b77 100644 --- a/hook.c +++ b/hook.c @@ -96,9 +96,13 @@ static int notify_hook_finished(int result, void *pp_task_cb) { struct hook_cb_data *hook_cb = pp_cb; + struct run_hooks_opt *opt = hook_cb->options; hook_cb->rc |= result; + if (opt->invoked_hook) + *opt->invoked_hook = 1; + return 0; } @@ -123,6 +127,9 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options) if (!options) BUG("a struct run_hooks_opt must be provided to run_hooks"); + if (options->invoked_hook) + *options->invoked_hook = 0; + if (!hook_path && !options->error_if_missing) goto cleanup; diff --git a/hook.h b/hook.h index 18d90aedf1..4258b13da0 100644 --- a/hook.h +++ b/hook.h @@ -18,6 +18,18 @@ struct run_hooks_opt * translates to "struct child_process"'s "dir" member. */ const char *dir; + + /** + * A pointer which if provided will be set to 1 or 0 depending + * on if a hook was started, regardless of whether or not that + * was successful. I.e. if the underlying start_command() was + * successful this will be set to 1. + * + * Used for avoiding TOCTOU races in code that would otherwise + * call hook_exist() after a "maybe hook run" to see if a hook + * was invoked. + */ + int *invoked_hook; }; #define RUN_HOOKS_OPT_INIT { \ diff --git a/sequencer.c b/sequencer.c index 35006c0cea..84eed9e96b 100644 --- a/sequencer.c +++ b/sequencer.c @@ -1220,7 +1220,7 @@ static int run_prepare_commit_msg_hook(struct repository *r, } else { arg1 = "message"; } - if (run_commit_hook(0, r->index_file, "prepare-commit-msg", name, + if (run_commit_hook(0, r->index_file, NULL, "prepare-commit-msg", name, arg1, arg2, NULL)) ret = error(_("'prepare-commit-msg' hook failed")); @@ -1552,7 +1552,7 @@ static int try_to_commit(struct repository *r, goto out; } - run_commit_hook(0, r->index_file, "post-commit", NULL); + run_commit_hook(0, r->index_file, NULL, "post-commit", NULL); if (flags & AMEND_MSG) commit_post_rewrite(r, current_head, oid);