executor: reserve fds that will belong to kcov

As now kcov instances may get set up during fuzzing, performing dup2 in
cover_open is no longer safe as it may close some important resource.
Prevent that by reserving most of fds that belong to the kcov fds range.

Unfortunately we must duplicate the code because of the way kcov
implementations are organized.

1 files changed, 8 insertions, 0 deletions

diff --git a/executor/executor_linux.h b/executor/executor_linux.h
index bd43f2a5b..7d2780c0f 100644
--- a/executor/executor_linux.h
+++ b/executor/executor_linux.h
@@ -147,6 +147,14 @@ static void cover_collect(cover_t* cov)
 		cov->size = *(uint32*)cov->data;
 }
 
+static void cover_reserve_fd(cover_t* cov)
+{
+	int fd = open("/dev/null", O_RDONLY);
+	if (fd < 0)
+		fail("failed to open /dev/null");
+	dup2(fd, cov->fd);
+}
+
 static bool use_cover_edges(uint32 pc)
 {
 	return true;