git: Support verifying commit signature post-sync

Add a new sync-git-verify-commit-signature option (defaulting to false)
that verifies the top commit signature after syncing. The verification
is currently done using built-in git routines.

The verification passes if the signature is good or untrusted.
In the latter case, a warning is printed. In any other case,
the verification causes sync to fail and an appropriate error is output.

Reviewed-by: Zac Medico <zmedico@gentoo.org>

man/portage.5

@@ -1007,6 +1007,10 @@ See also example for sync-git-clone-env.
 .B sync\-git\-pull\-extra\-opts
 Extra options to give to git when updating repository (git pull).
 .TP
+.B sync\-git\-verify\-commit\-signature = true|false
+Require the top commit in the repository to contain a good OpenPGP
+signature. Defaults to false.
+.TP
 .B sync\-hooks\-only\-on\-change
 If set to true, then sync of a given repository will not trigger postsync
 hooks unless hooks would have executed for a master repository or the

pym/portage/sync/modules/git/__init__.py

@@ -1,4 +1,4 @@
-# Copyright 2014-2017 Gentoo Foundation
+# Copyright 2014-2018 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 doc = """Git plug-in module for portage.
@@ -58,6 +58,7 @@ def _check_depth(self, attr):
 				'sync-git-env',
 				'sync-git-pull-env',
 				'sync-git-pull-extra-opts',
+				'sync-git-verify-commit-signature',
 				),
 		}
 	}

pym/portage/sync/modules/git/git.py

@@ -1,4 +1,4 @@
-# Copyright 2005-2017 Gentoo Foundation
+# Copyright 2005-2018 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 import logging
@@ -7,7 +7,7 @@
 import portage
 from portage import os
 from portage.util import writemsg_level, shlex_split
-from portage.output import create_color_func
+from portage.output import create_color_func, EOutput
 good = create_color_func("GOOD")
 bad = create_color_func("BAD")
 warn = create_color_func("WARN")
@@ -71,6 +71,7 @@ def new(self, **kwargs):
 		else:
 			# default
 			git_cmd_opts += " --depth 1"
+
 		if self.repo.module_specific_options.get('sync-git-clone-extra-opts'):
 			git_cmd_opts += " %s" % self.repo.module_specific_options['sync-git-clone-extra-opts']
 		git_cmd = "%s clone%s %s ." % (self.bin_command, git_cmd_opts,
@@ -85,6 +86,8 @@ def new(self, **kwargs):
 			self.logger(self.xterm_titles, msg)
 			writemsg_level(msg + "\n", level=logging.ERROR, noiselevel=-1)
 			return (exitcode, False)
+		if not self.verify_head():
+			return (1, False)
 		return (os.EX_OK, True)
 
 
@@ -125,12 +128,53 @@ def update(self):
 			self.logger(self.xterm_titles, msg)
 			writemsg_level(msg + "\n", level=logging.ERROR, noiselevel=-1)
 			return (exitcode, False)
+		if not self.verify_head():
+			return (1, False)
 
 		current_rev = subprocess.check_output(rev_cmd,
 			cwd=portage._unicode_encode(self.repo.location))
 
 		return (os.EX_OK, current_rev != previous_rev)
 
+	def verify_head(self):
+		if (self.repo.module_specific_options.get(
+				'sync-git-verify-commit-signature', 'false') != 'true'):
+			return True
+
+		rev_cmd = [self.bin_command, "log", "--pretty=format:%G?", "-1"]
+		try:
+			status = (portage._unicode_decode(
+				subprocess.check_output(rev_cmd,
+					cwd=portage._unicode_encode(self.repo.location)))
+				.strip())
+		except subprocess.CalledProcessError:
+			return False
+
+		out = EOutput()
+		if status == 'G':  # good signature is good
+			out.einfo('Trusted signature found on top commit')
+			return True
+		elif status == 'U':  # untrusted
+			out.ewarn('Top commit signature is valid but not trusted')
+			return True
+		else:
+			if status == 'B':
+				expl = 'bad signature'
+			elif status == 'X':
+				expl = 'expired signature'
+			elif status == 'Y':
+				expl = 'expired key'
+			elif status == 'R':
+				expl = 'revoked key'
+			elif status == 'E':
+				expl = 'unable to verify signature (missing key?)'
+			elif status == 'N':
+				expl = 'no signature'
+			else:
+				expl = 'unknown issue'
+			out.eerror('No valid signature found: %s' % (expl,))
+			return False
+
 	def retrieve_head(self, **kwargs):
 		'''Get information about the head commit'''
 		if kwargs: