Make git-fsck-cache check HEAD integrity

In particular, check that it's a symlink, and points to refs/heads/.  We
depend on that these days not only for "git checkout", but also because
fsck and others only check for references in the .git/refs/
subdirectory, not things like HEAD itself.

diff --git a/fsck-cache.c b/fsck-cache.c
index 9867fa6..e42264e 100644 (file)
--- a/fsck-cache.c
+++ b/fsck-cache.c
@@ -342,6 +342,31 @@ static void fsck_object_dir(const char *path)
        fsck_sha1_list();
 }
 
+static int fsck_head_link(void)
+{
+       int fd, count;
+       char hex[40];
+       unsigned char sha1[20];
+       static char path[PATH_MAX], link[PATH_MAX];
+       const char *git_dir = gitenv(GIT_DIR_ENVIRONMENT) ? : DEFAULT_GIT_DIR_ENVIRONMENT;
+
+       snprintf(path, sizeof(path), "%s/HEAD", git_dir);
+       if (readlink(path, link, sizeof(link)) < 0)
+               return error("HEAD is not a symlink");
+       if (strncmp("refs/heads/", link, 11))
+               return error("HEAD points to something strange (%s)", link);
+       fd = open(path, O_RDONLY);
+       if (fd < 0)
+               return error("HEAD: %s", strerror(errno));
+       count = read(fd, hex, sizeof(hex));
+       close(fd);
+       if (count < 0)
+               return error("HEAD: %s", strerror(errno));
+       if (count < 40 || get_sha1_hex(hex, sha1))
+               return error("HEAD: not a valid git pointer");
+       return 0;
+}
+
 int main(int argc, char **argv)
 {
        int i, heads;
@@ -382,6 +407,7 @@ int main(int argc, char **argv)
        if (standalone)
                unsetenv("GIT_ALTERNATE_OBJECT_DIRECTORIES");
 
+       fsck_head_link();
        fsck_object_dir(get_object_directory());
        if (check_full) {
                int j;