From 8659477ea65b1617332efee6da4c533137870577 Mon Sep 17 00:00:00 2001
From: Vladis Dronov <vdronov@redhat.com>
Date: Sat, 12 Jun 2021 09:00:42 +0200
Subject: Fix a read() returning zero case in init_entropy_source()

Covscan warns about this with:

Error: CHECKED_RETURN (CWE-252): [#def3]
rng-tools-6.12/rngd_entsource.c:185: check_return: "read(int, void *,
size_t)" returns the number of bytes read, but it is ignored.
    185|-> if (read(rngavail_fd, buf, sizeof(buf)) < 0) {

Add a check for a zero return. While this should not happen, lets just
handle the case, also to silence covscan.

Signed-off-by: Vladis Dronov <vdronov@redhat.com>
---
 rngd_entsource.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/rngd_entsource.c b/rngd_entsource.c
index f54ee40..e5b7d43 100644
--- a/rngd_entsource.c
+++ b/rngd_entsource.c
@@ -182,13 +182,14 @@ int init_entropy_source(struct rng *ent_src)
 		return 1;
 	}
 
-	if (read(rngavail_fd, buf, sizeof(buf)) < 0) {
+	int ret = read(rngavail_fd, buf, sizeof(buf));
+	if (ret < 0) {
 		message_entsrc(ent_src,LOG_DAEMON|LOG_DEBUG, "Error reading sysfs file: %s\n", RNG_AVAIL);
 		close(rngavail_fd);
 		return 1;
 	}
 
-	if (strncmp(buf, "\n", 1) == 0) {
+	if (ret == 0 || strncmp(buf, "\n", 1) == 0) {
 		message_entsrc(ent_src,LOG_DAEMON|LOG_DEBUG, "No available rng device\n");
 		close(rngavail_fd);
 		return 1;
-- 
2.26.3