check_icmp: prevent segfault on OpenBSD (#2224)HEADmaster

* check_icmp: prevent segfault on OpenBSD

This commit adds a sanity check for sockets in
check_icmp.
Previously FD_ISSET segfaulted when a socket value was
-1 (on OpenBSD). The changes here add an explicit
check whether the socket is -1 (and therefore not
set).

---------

Co-authored-by: Lorenz Kästle <lorenz.kaestle@netways.de>

1 files changed, 5 insertions, 2 deletions

diff --git a/plugins-root/check_icmp.c b/plugins-root/check_icmp.c
index 58d8a545..5bfb5cb5 100644
--- a/plugins-root/check_icmp.c
+++ b/plugins-root/check_icmp.c
@@ -1470,10 +1470,13 @@ static recvfrom_wto_wrapper recvfrom_wto(const check_icmp_socket_set sockset, vo
         };
 
         ssize_t ret;
-        if (FD_ISSET(sockset.socket4, &read_fds)) {
+
+        // Test explicitly whether sockets are in use
+        // this is necessary at least on OpenBSD where FD_ISSET will segfault otherwise
+        if ((sockset.socket4 != -1) && FD_ISSET(sockset.socket4, &read_fds)) {
                 ret = recvmsg(sockset.socket4, &hdr, 0);
                 result.recv_proto = AF_INET;
-        } else if (FD_ISSET(sockset.socket6, &read_fds)) {
+        } else if ((sockset.socket6 != -1) && FD_ISSET(sockset.socket6, &read_fds)) {
                 ret = recvmsg(sockset.socket6, &hdr, 0);
                 result.recv_proto = AF_INET6;
         } else {