test get_git_work_tree() return value for NULL

If we are in a git directory, get_git_work_tree() can return NULL.
While trying to determine whether or not the given paths are outside
the work tree, the following command would read from it anyways and
trigger a segmentation fault.

 git diff / /

Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/diff-no-index.c b/diff-no-index.c
index aae8e7accc1ff955bd76c62b379b37f343f61cc4..4cd9dacbe8e98d1420ebe1a217b0f927d24d125a 100644 (file)
--- a/diff-no-index.c
+++ b/diff-no-index.c
@@ -150,16 +150,14 @@ static int queue_diff(struct diff_options *o,
 
 static int path_outside_repo(const char *path)
 {
-       /*
-        * We have already done setup_git_directory_gently() so we
-        * know we are inside a git work tree already.
-        */
        const char *work_tree;
        size_t len;
 
        if (!is_absolute_path(path))
                return 0;
        work_tree = get_git_work_tree();
+       if (!work_tree)
+               return 1;
        len = strlen(work_tree);
        if (strncmp(path, work_tree, len) ||
            (path[len] != '\0' && path[len] != '/'))