Re: [PATCH 3/3] verify-commit: scriptable commit signature verification

>Commit signatures can be verified using "git show -s --show-signature"
>or the "%G?" pretty format and parsing the output, which is well suited
>for user inspection, but not for scripting.
>
>Provide a command "verify-commit" which is analogous to "verify-tag":
>It
>returns 0 for good signatures and non-zero otherwise, has the gpg
>output
>on stderr and (optionally) the commit object on stdout, sans the
>signature, just like "verify-tag" does.
>
>Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
>---
> Documentation/git-verify-commit.txt | 28 +++++++++++
> Makefile                            |  1 +
> builtin.h                           |  1 +
>builtin/verify-commit.c             | 98
>+++++++++++++++++++++++++++++++++++++
> command-list.txt                    |  1 +
> git.c                               |  1 +
> 6 files changed, 130 insertions(+)
> create mode 100644 Documentation/git-verify-commit.txt
> create mode 100644 builtin/verify-commit.c
>
>diff --git a/Documentation/git-verify-commit.txt
>b/Documentation/git-verify-commit.txt
>new file mode 100644
>index 0000000..dcd7803
>--- /dev/null
>+++ b/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
>diff --git a/Makefile b/Makefile
>index 07ea105..b92418d 100644
>--- a/Makefile
>+++ b/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
>diff --git a/builtin.h b/builtin.h
>index c47c110..5d91f31 100644
>--- a/builtin.h
>+++ b/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);
>diff --git a/builtin/verify-commit.c b/builtin/verify-commit.c
>new file mode 100644
>index 0000000..69b7c6d
>--- /dev/null
>+++ b/builtin/verify-commit.c
>@@ -0,0 +1,98 @@
>+/*
>+ * 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);
>+
>+	free(signature_check.gpg_output);
>+	free(signature_check.gpg_status);
>+	free(signature_check.signer);
>+	free(signature_check.key);
>+	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);
>+
>+	type = sha1_object_info(sha1, NULL);
>+	if (type != OBJ_COMMIT)
>+		return error("%s: cannot verify a non-commit object of type %s.",
>+				name, typename(type));
>+
>+	buf = read_sha1_file(sha1, &type, &size);
>+	if (!buf)
>+		return error("%s: unable to read file.", name);
>+
>+	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;
>+}
>diff --git a/command-list.txt b/command-list.txt
>index cf36c3d..a3ff0c9 100644
>--- a/command-list.txt
>+++ b/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
>diff --git a/git.c b/git.c
>index 7780572..bbc3293 100644
>--- a/git.c
>+++ b/git.c
>@@ -441,6 +441,7 @@ 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 },