Fix race conditions in signal handling

Avoid several race conditions by using distinct variables for the different
signals. In particular different signals received in quick succession don't
overwrite each other any more, and odhcp6c_signal_process doesn't return true
anymore when a new SIGIO is received while another is still being processed.

diff --git a/src/odhcp6c.c b/src/odhcp6c.c
index bf61d5077f86dec88f9f4715e3c65fd8f8f4d48f..e9937ad633f9724495a679a1318ee78120117c7c 100644 (file)
--- a/src/odhcp6c.c
+++ b/src/odhcp6c.c
@@ -43,7 +43,11 @@ static int usage(void);
 static uint8_t *state_data[_STATE_MAX] = {NULL};
 static size_t state_len[_STATE_MAX] = {0};
 
-static volatile int do_signal = 0;
+static volatile bool signal_io = false;
+static volatile bool signal_usr1 = false;
+static volatile bool signal_usr2 = false;
+static volatile bool signal_term = false;
+
 static int urandom_fd = -1, allow_slaac_only = 0;
 static bool bound = false, release = true;
 static time_t last_update = 0;
@@ -217,7 +221,7 @@ int main(_unused int argc, char* const argv[])
 
        script_call("started");
 
-       while (do_signal != SIGTERM) { // Main logic
+       while (!signal_term) { // Main logic
                odhcp6c_clear_state(STATE_SERVER_ID);
                odhcp6c_clear_state(STATE_IA_NA);
                odhcp6c_clear_state(STATE_IA_PD);
@@ -230,7 +234,7 @@ int main(_unused int argc, char* const argv[])
 
                syslog(LOG_NOTICE, "(re)starting transaction on %s", ifname);
 
-               do_signal = 0;
+               signal_usr1 = signal_usr2 = false;
                int mode = dhcpv6_request(DHCPV6_MSG_SOLICIT);
                odhcp6c_signal_process();
 
@@ -240,11 +244,11 @@ int main(_unused int argc, char* const argv[])
                do {
                        int res = dhcpv6_request(mode == DHCPV6_STATELESS ?
                                        DHCPV6_MSG_INFO_REQ : DHCPV6_MSG_REQUEST);
+                       bool signalled = odhcp6c_signal_process();
 
-                       odhcp6c_signal_process();
                        if (res > 0)
                                break;
-                       else if (do_signal > 0) {
+                       else if (signalled) {
                                mode = -1;
                                break;
                        }
@@ -260,8 +264,8 @@ int main(_unused int argc, char* const argv[])
                        bound = true;
                        syslog(LOG_NOTICE, "entering stateless-mode on %s", ifname);
 
-                       while (do_signal == 0 || do_signal == SIGUSR1) {
-                               do_signal = 0;
+                       while (!signal_usr2 && !signal_term) {
+                               signal_usr1 = false;
                                script_call("informed");
 
                                int res = dhcpv6_poll_reconfigure();
@@ -270,15 +274,16 @@ int main(_unused int argc, char* const argv[])
                                if (res > 0)
                                        continue;
 
-                               if (do_signal == SIGUSR1) {
-                                       do_signal = 0; // Acknowledged
+                               if (signal_usr1) {
+                                       signal_usr1 = false; // Acknowledged
                                        continue;
-                               } else if (do_signal > 0)
+                               }
+                               if (signal_usr2 || signal_term)
                                        break;
 
                                res = dhcpv6_request(DHCPV6_MSG_INFO_REQ);
                                odhcp6c_signal_process();
-                               if (do_signal == SIGUSR1)
+                               if (signal_usr1)
                                        continue;
                                else if (res < 0)
                                        break;
@@ -294,7 +299,7 @@ int main(_unused int argc, char* const argv[])
                                bfd_start(ifname, bfd_loss, bfd_interval);
 #endif
 
-                       while (do_signal == 0 || do_signal == SIGUSR1) {
+                       while (!signal_usr2 && !signal_term) {
                                // Renew Cycle
                                // Wait for T1 to expire or until we get a reconfigure
                                int res = dhcpv6_poll_reconfigure();
@@ -305,9 +310,9 @@ int main(_unused int argc, char* const argv[])
                                }
 
                                // Handle signal, if necessary
-                               if (do_signal == SIGUSR1)
-                                       do_signal = 0; // Acknowledged
-                               else if (do_signal > 0)
+                               if (signal_usr1)
+                                       signal_usr1 = false; // Acknowledged
+                               if (signal_usr2 || signal_term)
                                        break; // Other signal type
 
                                // Send renew as T1 expired
@@ -427,12 +432,13 @@ static uint8_t* odhcp6c_resize_state(enum odhcp6c_state state, ssize_t len)
 
 bool odhcp6c_signal_process(void)
 {
-       if (do_signal == SIGIO) {
-               do_signal = 0;
+       while (signal_io) {
+               signal_io = false;
+
                bool ra_updated = ra_process();
 
                if (ra_link_up())
-                       do_signal = SIGUSR2;
+                       signal_usr2 = true;
 
                if (ra_updated && (bound || allow_slaac_only == 0))
                        script_call("ra-updated"); // Immediate process urgent events
@@ -444,7 +450,7 @@ bool odhcp6c_signal_process(void)
 #endif
        }
 
-       return do_signal != 0;
+       return signal_usr1 || signal_usr2 || signal_term;
 }
 
 
@@ -624,11 +630,11 @@ static void sighandler(int signal)
        if (signal == SIGCHLD)
                while (waitpid(-1, NULL, WNOHANG) > 0);
        else if (signal == SIGUSR1)
-               do_signal = SIGUSR1;
+               signal_usr1 = true;
        else if (signal == SIGUSR2)
-               do_signal = SIGUSR2;
+               signal_usr2 = true;
        else if (signal == SIGIO)
-               do_signal = SIGIO;
+               signal_io = true;
        else
-               do_signal = SIGTERM;
+               signal_term = true;
 }