bftw: Make sure we don't close a directory while we unwrap it

bftw_cache_reserve() can lead to bftw_cache_pop(), which could close the
directory we're trying to unwrap!  If that happened, we would try
dup_cloexec(-1), which would fail with EBADF, so there was no observable
bug.  But it's better to avoid the whole situation.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/bftw.c b/src/bftw.c
index 1995e12..06a0085 100644
--- a/src/bftw.c
+++ b/src/bftw.c
@@ -811,8 +811,12 @@ static int bftw_unwrapdir(struct bftw_state *state, struct bftw_file *file) {
 		return bftw_close(state, file);
 	}
 
-	if (bftw_cache_reserve(state) != 0) {
-		return -1;
+	// Make room for dup()
+	bftw_cache_pin(cache, file);
+	int ret = bftw_cache_reserve(state);
+	bftw_cache_unpin(cache, file);
+	if (ret != 0) {
+		return ret;
 	}
 
 	int fd = dup_cloexec(file->fd);