git-serve: check update hook permissions

Verify that the update hook exists and is executable before running Git
to prevent from broken repositories when permissions are broken.
Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

aurweb/exceptions.py

@@ -16,6 +16,12 @@ class PermissionDeniedException(AurwebException):
         super(PermissionDeniedException, self).__init__(msg)
 
 
+class BrokenUpdateHookException(AurwebException):
+    def __init__(self, cmd):
+        msg = 'broken update hook: {:s}'.format(cmd)
+        super(BrokenUpdateHookException, self).__init__(msg)
+
+
 class InvalidUserException(AurwebException):
     def __init__(self, user):
         msg = 'unknown user: {:s}'.format(user)

aurweb/git/serve.py

@@ -496,6 +496,9 @@ def serve(action, cmdargv, user, privileged, remote_addr):
             if not privileged and not pkgbase_has_write_access(pkgbase, user):
                 raise aurweb.exceptions.PermissionDeniedException(user)
 
+        if not os.access(git_update_cmd, os.R_OK | os.X_OK):
+            raise aurweb.exceptions.BrokenUpdateHookException(git_update_cmd)
+
         os.environ["AUR_USER"] = user
         os.environ["AUR_PKGBASE"] = pkgbase
         os.environ["GIT_NAMESPACE"] = pkgbase