add OpenBSD unveil support

The unveil() system call first appeared in OpenBSD 6.4.

For stagit it has the following properties now:

- stagit-index: only read-access to the file-system for the specified
  directories/repositories.
- stagit: read-access to the specified directory/repository.
  read-write and creation access to the current directory for the output files.
  read-write and creation access to the specified cache file.

1 files changed, 7 insertions, 0 deletions

diff --git a/stagit.c b/stagit.c
index a6cfebc..dcac016 100644
--- a/stagit.c
+++ b/stagit.c
@@ -1095,6 +1095,13 @@ main(int argc, char *argv[])
 	git_libgit2_init();
 
 #ifdef __OpenBSD__
+	if (unveil(repodir, "r") == -1)
+		err(1, "unveil: %s", repodir);
+	if (unveil(".", "rwc") == -1)
+		err(1, "unveil: .");
+	if (cachefile && unveil(cachefile, "rwc") == -1)
+		err(1, "unveil: %s", cachefile);
+
 	if (cachefile) {
 		if (pledge("stdio rpath wpath cpath fattr", NULL) == -1)
 			err(1, "pledge");