Merge branch 'mg/verify-commit'

Add 'verify-commit' to be used in a way similar to 'verify-tag' is
used.  Further work on verifying the mergetags might be needed.

* mg/verify-commit:
  t7510: test verify-commit
  t7510: exit for loop with test result
  verify-commit: scriptable commit signature verification
  gpg-interface: provide access to the payload
  gpg-interface: provide clear helper for struct signature_check

Documentation/git-verify-commit.txt

@@ -0,0 +1,28 @@
+git-verify-commit(1)
+====================
+
+NAME
+----
+git-verify-commit - Check the GPG signature of commits
+
+SYNOPSIS
+--------
+[verse]
+'git verify-commit' <commit>...
+
+DESCRIPTION
+-----------
+Validates the gpg signature created by 'git commit -S'.
+
+OPTIONS
+-------
+-v::
+--verbose::
+	Print the contents of the commit object before validating it.
+
+<commit>...::
+	SHA-1 identifiers of Git commit objects.
+
+GIT
+---
+Part of the linkgit:git[1] suite

Makefile

@@ -999,6 +999,7 @@ BUILTIN_OBJS += builtin/update-ref.o
 BUILTIN_OBJS += builtin/update-server-info.o
 BUILTIN_OBJS += builtin/upload-archive.o
 BUILTIN_OBJS += builtin/var.o
+BUILTIN_OBJS += builtin/verify-commit.o
 BUILTIN_OBJS += builtin/verify-pack.o
 BUILTIN_OBJS += builtin/verify-tag.o
 BUILTIN_OBJS += builtin/write-tree.o

builtin.h

@@ -128,6 +128,7 @@ extern int cmd_update_server_info(int argc, const char **argv, const char *prefi
 extern int cmd_upload_archive(int argc, const char **argv, const char *prefix);
 extern int cmd_upload_archive_writer(int argc, const char **argv, const char *prefix);
 extern int cmd_var(int argc, const char **argv, const char *prefix);
+extern int cmd_verify_commit(int argc, const char **argv, const char *prefix);
 extern int cmd_verify_tag(int argc, const char **argv, const char *prefix);
 extern int cmd_version(int argc, const char **argv, const char *prefix);
 extern int cmd_whatchanged(int argc, const char **argv, const char *prefix);

builtin/merge.c

@@ -1282,10 +1282,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 				printf(_("Commit %s has a good GPG signature by %s\n"),
 				       hex, signature_check.signer);
 
-			free(signature_check.gpg_output);
-			free(signature_check.gpg_status);
-			free(signature_check.signer);
-			free(signature_check.key);
+			signature_check_clear(&signature_check);
 		}
 	}
 

builtin/verify-commit.c

@@ -0,0 +1,93 @@
+/*
+ * Builtin "git commit-commit"
+ *
+ * Copyright (c) 2014 Michael J Gruber <git@drmicha.warpmail.net>
+ *
+ * Based on git-verify-tag
+ */
+#include "cache.h"
+#include "builtin.h"
+#include "commit.h"
+#include "run-command.h"
+#include <signal.h>
+#include "parse-options.h"
+#include "gpg-interface.h"
+
+static const char * const verify_commit_usage[] = {
+		N_("git verify-commit [-v|--verbose] <commit>..."),
+		NULL
+};
+
+static int run_gpg_verify(const unsigned char *sha1, const char *buf, unsigned long size, int verbose)
+{
+	struct signature_check signature_check;
+
+	memset(&signature_check, 0, sizeof(signature_check));
+
+	check_commit_signature(lookup_commit(sha1), &signature_check);
+
+	if (verbose && signature_check.payload)
+		fputs(signature_check.payload, stdout);
+
+	if (signature_check.gpg_output)
+		fputs(signature_check.gpg_output, stderr);
+
+	signature_check_clear(&signature_check);
+	return signature_check.result != 'G';
+}
+
+static int verify_commit(const char *name, int verbose)
+{
+	enum object_type type;
+	unsigned char sha1[20];
+	char *buf;
+	unsigned long size;
+	int ret;
+
+	if (get_sha1(name, sha1))
+		return error("commit '%s' not found.", name);
+
+	buf = read_sha1_file(sha1, &type, &size);
+	if (!buf)
+		return error("%s: unable to read file.", name);
+	if (type != OBJ_COMMIT)
+		return error("%s: cannot verify a non-commit object of type %s.",
+				name, typename(type));
+
+	ret = run_gpg_verify(sha1, buf, size, verbose);
+
+	free(buf);
+	return ret;
+}
+
+static int git_verify_commit_config(const char *var, const char *value, void *cb)
+{
+	int status = git_gpg_config(var, value, cb);
+	if (status)
+		return status;
+	return git_default_config(var, value, cb);
+}
+
+int cmd_verify_commit(int argc, const char **argv, const char *prefix)
+{
+	int i = 1, verbose = 0, had_error = 0;
+	const struct option verify_commit_options[] = {
+		OPT__VERBOSE(&verbose, N_("print commit contents")),
+		OPT_END()
+	};
+
+	git_config(git_verify_commit_config, NULL);
+
+	argc = parse_options(argc, argv, prefix, verify_commit_options,
+			     verify_commit_usage, PARSE_OPT_KEEP_ARGV0);
+	if (argc <= i)
+		usage_with_options(verify_commit_usage, verify_commit_options);
+
+	/* sometimes the program was terminated because this signal
+	 * was received in the process of writing the gpg input: */
+	signal(SIGPIPE, SIG_IGN);
+	while (i < argc)
+		if (verify_commit(argv[i++], verbose))
+			had_error = 1;
+	return had_error;
+}

command-list.txt

@@ -132,6 +132,7 @@ git-update-server-info                  synchingrepositories
 git-upload-archive                      synchelpers
 git-upload-pack                         synchelpers
 git-var                                 plumbinginterrogators
+git-verify-commit                       ancillaryinterrogators
 git-verify-pack                         plumbinginterrogators
 git-verify-tag                          ancillaryinterrogators
 gitweb                                  ancillaryinterrogators

commit.c

@@ -1270,6 +1270,7 @@ void check_commit_signature(const struct commit* commit, struct signature_check
 				      &gpg_output, &gpg_status);
 	if (status && !gpg_output.len)
 		goto out;
+	sigc->payload = strbuf_detach(&payload, NULL);
 	sigc->gpg_output = strbuf_detach(&gpg_output, NULL);
 	sigc->gpg_status = strbuf_detach(&gpg_status, NULL);
 	parse_gpg_output(sigc);

git.c

@@ -478,6 +478,7 @@ static struct cmd_struct commands[] = {
 	{ "upload-archive", cmd_upload_archive },
 	{ "upload-archive--writer", cmd_upload_archive_writer },
 	{ "var", cmd_var, RUN_SETUP_GENTLY },
+	{ "verify-commit", cmd_verify_commit, RUN_SETUP },
 	{ "verify-pack", cmd_verify_pack },
 	{ "verify-tag", cmd_verify_tag, RUN_SETUP },
 	{ "version", cmd_version },

gpg-interface.c

@@ -7,6 +7,20 @@
 static char *configured_signing_key;
 static const char *gpg_program = "gpg";
 
+void signature_check_clear(struct signature_check *sigc)
+{
+	free(sigc->payload);
+	free(sigc->gpg_output);
+	free(sigc->gpg_status);
+	free(sigc->signer);
+	free(sigc->key);
+	sigc->payload = NULL;
+	sigc->gpg_output = NULL;
+	sigc->gpg_status = NULL;
+	sigc->signer = NULL;
+	sigc->key = NULL;
+}
+
 void set_signing_key(const char *key)
 {
 	free(configured_signing_key);

gpg-interface.h

@@ -2,6 +2,7 @@
 #define GPG_INTERFACE_H
 
 struct signature_check {
+	char *payload;
 	char *gpg_output;
 	char *gpg_status;
 	char result; /* 0 (not checked),
@@ -13,6 +14,7 @@ struct signature_check {
 	char *key;
 };
 
+extern void signature_check_clear(struct signature_check *sigc);
 extern int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key);
 extern int verify_signed_buffer(const char *payload, size_t payload_size, const char *signature, size_t signature_size, struct strbuf *gpg_output, struct strbuf *gpg_status);
 extern int git_gpg_config(const char *, const char *, void *);

pretty.c

@@ -1520,8 +1520,6 @@ void format_commit_message(const struct commit *commit,
 
 	free(context.commit_encoding);
 	unuse_commit_buffer(commit, context.message);
-	free(context.signature_check.gpg_output);
-	free(context.signature_check.signer);
 }
 
 static void pp_header(struct pretty_print_context *pp,

t/t7510-signed-commit.sh

@@ -48,10 +48,11 @@ test_expect_success GPG 'create signed commits' '
 	git tag eighth-signed-alt
 '
 
-test_expect_success GPG 'show signatures' '
+test_expect_success GPG 'verify and show signatures' '
 	(
 		for commit in initial second merge fourth-signed fifth-signed sixth-signed seventh-signed
 		do
+			git verify-commit $commit &&
 			git show --pretty=short --show-signature $commit >actual &&
 			grep "Good signature from" actual &&
 			! grep "BAD signature from" actual &&
@@ -61,6 +62,7 @@ test_expect_success GPG 'show signatures' '
 	(
 		for commit in merge^2 fourth-unsigned sixth-unsigned seventh-unsigned
 		do
+			test_must_fail git verify-commit $commit &&
 			git show --pretty=short --show-signature $commit >actual &&
 			! grep "Good signature from" actual &&
 			! grep "BAD signature from" actual &&
@@ -79,11 +81,25 @@ test_expect_success GPG 'show signatures' '
 	)
 '
 
+test_expect_success GPG 'show signed commit with signature' '
+	git show -s initial >commit &&
+	git show -s --show-signature initial >show &&
+	git verify-commit -v initial >verify.1 2>verify.2 &&
+	git cat-file commit initial >cat &&
+	grep -v "gpg: " show >show.commit &&
+	grep "gpg: " show >show.gpg &&
+	grep -v "^ " cat | grep -v "^gpgsig " >cat.commit &&
+	test_cmp show.commit commit &&
+	test_cmp show.gpg verify.2 &&
+	test_cmp cat.commit verify.1
+'
+
 test_expect_success GPG 'detect fudged signature' '
 	git cat-file commit seventh-signed >raw &&
 
 	sed -e "s/seventh/7th forged/" raw >forged1 &&
 	git hash-object -w -t commit forged1 >forged1.commit &&
+	! git verify-commit $(cat forged1.commit) &&
 	git show --pretty=short --show-signature $(cat forged1.commit) >actual1 &&
 	grep "BAD signature from" actual1 &&
 	! grep "Good signature from" actual1
@@ -94,6 +110,7 @@ test_expect_success GPG 'detect fudged signature with NUL' '
 	cat raw >forged2 &&
 	echo Qwik | tr "Q" "\000" >>forged2 &&
 	git hash-object -w -t commit forged2 >forged2.commit &&
+	! git verify-commit $(cat forged2.commit) &&
 	git show --pretty=short --show-signature $(cat forged2.commit) >actual2 &&
 	grep "BAD signature from" actual2 &&
 	! grep "Good signature from" actual2
@@ -102,6 +119,7 @@ test_expect_success GPG 'detect fudged signature with NUL' '
 test_expect_success GPG 'amending already signed commit' '
 	git checkout fourth-signed^0 &&
 	git commit --amend -S --no-edit &&
+	git verify-commit HEAD &&
 	git show -s --show-signature HEAD >actual &&
 	grep "Good signature from" actual &&
 	! grep "BAD signature from" actual