Keep snapshots working under a global git config

cgit unsets HOME to isolate git from the calling user, but git still
finds the global config through its getpwuid fallback and then dies
expanding a `~` in `core.excludesfile`. That die happened after the
snapshot headers and the gzip filter were already in place, so the
error page was compressed into the archive and every snapshot came
out undecompressable.

1 file changed, 7 insertions, 1 deletion

diff --git a/source/cgit.c b/source/cgit.c
index 156d2a7..909e120 100644
--- a/source/cgit.c
+++ b/source/cgit.c
@@ -24,8 +24,14 @@ const char *cgit_version = CGIT_VERSION;
 __attribute__((constructor))
 static void constructor_environment()
 {
-	/* Do not look in /etc/ for gitconfig and gitattributes. */
+	/*
+	 * Isolate git from the calling user's configuration. Ignore the
+	 * system and global config and attributes, so a snapshot cannot be
+	 * broken by something like a core.excludesfile pointing at a "~" path
+	 * that git can no longer expand once HOME is unset below.
+	 */
 	setenv("GIT_CONFIG_NOSYSTEM", "1", 1);
+	setenv("GIT_CONFIG_GLOBAL", "/dev/null", 1);
 	setenv("GIT_ATTR_NOSYSTEM", "1", 1);
 	unsetenv("HOME");
 	unsetenv("XDG_CONFIG_HOME");