config: disallow relative include paths from blobs

When we see a relative config include like:

  [include]
  path = foo

we make it relative to the containing directory of the file
that contains the snippet. This makes no sense for config
read from a blob, as it is not on the filesystem.  Something
like "HEAD:some/path" could have a relative path within the
tree, but:

  1. It would not be part of include.path, which explicitly
     refers to the filesystem.

  2. It would need different parsing rules anyway to
     determine that it is a tree path.

The current code just uses the "name" field, which is wrong.
Let's split that into "name" and "path" fields, use the
latter for relative includes, and fill in only the former
for blobs.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -21,6 +21,7 @@ struct config_source {
 		} buf;
 	} u;
 	const char *name;
+	const char *path;
 	int die_on_error;
 	int linenr;
 	int eof;
@@ -97,12 +98,12 @@ static int handle_path_include(const char *path, struct config_include_data *inc
 	if (!is_absolute_path(path)) {
 		char *slash;
 
-		if (!cf || !cf->name)
+		if (!cf || !cf->path)
 			return error("relative config includes must come from files");
 
-		slash = find_last_dir_sep(cf->name);
+		slash = find_last_dir_sep(cf->path);
 		if (slash)
-			strbuf_add(&buf, cf->name, slash - cf->name + 1);
+			strbuf_add(&buf, cf->path, slash - cf->path + 1);
 		strbuf_addstr(&buf, path);
 		path = buf.buf;
 	}
@@ -1040,7 +1041,7 @@ int git_config_from_file(config_fn_t fn, const char *filename, void *data)
 		struct config_source top;
 
 		top.u.file = f;
-		top.name = filename;
+		top.name = top.path = filename;
 		top.die_on_error = 1;
 		top.do_fgetc = config_file_fgetc;
 		top.do_ungetc = config_file_ungetc;
@@ -1062,6 +1063,7 @@ int git_config_from_buf(config_fn_t fn, const char *name, const char *buf,
 	top.u.buf.len = len;
 	top.u.buf.pos = 0;
 	top.name = name;
+	top.path = NULL;
 	top.die_on_error = 0;
 	top.do_fgetc = config_buf_fgetc;
 	top.do_ungetc = config_buf_ungetc;

t/t1305-config-include.sh

@@ -122,6 +122,22 @@ test_expect_success 'relative includes from command line fail' '
 	test_must_fail git -c include.path=one config test.one
 '
 
+test_expect_success 'absolute includes from blobs work' '
+	echo "[test]one = 1" >one &&
+	echo "[include]path=$(pwd)/one" >blob &&
+	blob=$(git hash-object -w blob) &&
+	echo 1 >expect &&
+	git config --blob=$blob test.one >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'relative includes from blobs fail' '
+	echo "[test]one = 1" >one &&
+	echo "[include]path=one" >blob &&
+	blob=$(git hash-object -w blob) &&
+	test_must_fail git config --blob=$blob test.one
+'
+
 test_expect_success 'include cycles are detected' '
 	cat >.gitconfig <<-\EOF &&
 	[test]value = gitconfig