bugfix: check if the worker_connections is 0 before privileged agent spawning. (#786)

The core dump may occur during initialization

    Program terminated with signal SIGSEGV, Segmentation fault.
    #0  0x0000000000441711 in ngx_event_process_init (cycle=0x1e93cc0) at src/event/ngx_event.c:807
    801         i = cycle->connection_n;
    802         next = NULL;
    803
    804         do {
    805             i--;
    806
    807             c[i].data = next;
    #1  0x000000000044abb9 in ngx_worker_process_init (cycle=cycle@entry=0x1e93cc0, worker=worker@entry=-1) at src/os/unix/ngx_process_cycle.c:968

patches/nginx-1.19.3-privileged_agent_process_connections.patch

@@ -51,3 +51,23 @@ index b1eb322..8e03696 100644
  
      ngx_worker_process_init(cycle, -1);
  
+diff --git a/src/os/unix/ngx_process_cycle.c b/src/os/unix/ngx_process_cycle.c
+index df25f9d..bd259c1 100644
+--- a/src/os/unix/ngx_process_cycle.c
++++ b/src/os/unix/ngx_process_cycle.c
+@@ -442,6 +442,15 @@
+         return;
+     }
+ 
++    /* 0 is an illegal value and may result in a core dump later */
++    if (ccf->privileged_agent_connections == 0) {
++        ngx_log_error(NGX_LOG_ALERT, cycle->log, 0,
++                      "%ui worker_connection is not enough, "
++                      "privileged agent process cannot be spawned",
++                      ccf->privileged_agent_connections);
++        return;
++    }
++
+     ngx_spawn_process(cycle, ngx_privileged_agent_process_cycle,
+                       "privileged agent process", "privileged agent process",
+                       respawn ? NGX_PROCESS_JUST_RESPAWN : NGX_PROCESS_RESPAWN);

patches/nginx-1.19.9-privileged_agent_process_connections.patch

@@ -51,3 +51,23 @@ index df25f9d..bd259c1 100644
  
      ngx_worker_process_init(cycle, -1);
  
+diff --git a/src/os/unix/ngx_process_cycle.c b/src/os/unix/ngx_process_cycle.c
+index df25f9d..bd259c1 100644
+--- a/src/os/unix/ngx_process_cycle.c
++++ b/src/os/unix/ngx_process_cycle.c
+@@ -442,6 +442,15 @@
+         return;
+     }
+ 
++    /* 0 is an illegal value and may result in a core dump later */
++    if (ccf->privileged_agent_connections == 0) {
++        ngx_log_error(NGX_LOG_ALERT, cycle->log, 0,
++                      "%ui worker_connection is not enough, "
++                      "privileged agent process cannot be spawned",
++                      ccf->privileged_agent_connections);
++        return;
++    }
++
+     ngx_spawn_process(cycle, ngx_privileged_agent_process_cycle,
+                       "privileged agent process", "privileged agent process",
+                       respawn ? NGX_PROCESS_JUST_RESPAWN : NGX_PROCESS_RESPAWN);

patches/nginx-1.21.3-privileged_agent_process_connections.patch

@@ -51,3 +51,23 @@ index df25f9d..bd259c1 100644
  
      ngx_worker_process_init(cycle, -1);
  
+diff --git a/src/os/unix/ngx_process_cycle.c b/src/os/unix/ngx_process_cycle.c
+index df25f9d..bd259c1 100644
+--- a/src/os/unix/ngx_process_cycle.c
++++ b/src/os/unix/ngx_process_cycle.c
+@@ -442,6 +442,15 @@
+         return;
+     }
+ 
++    /* 0 is an illegal value and may result in a core dump later */
++    if (ccf->privileged_agent_connections == 0) {
++        ngx_log_error(NGX_LOG_ALERT, cycle->log, 0,
++                      "%ui worker_connection is not enough, "
++                      "privileged agent process cannot be spawned",
++                      ccf->privileged_agent_connections);
++        return;
++    }
++
+     ngx_spawn_process(cycle, ngx_privileged_agent_process_cycle,
+                       "privileged agent process", "privileged agent process",
+                       respawn ? NGX_PROCESS_JUST_RESPAWN : NGX_PROCESS_RESPAWN);

patches/nginx-1.21.4-privileged_agent_process_connections.patch

@@ -51,3 +51,23 @@ index df25f9d..bd259c1 100644
  
      ngx_worker_process_init(cycle, -1);
  
+diff --git a/src/os/unix/ngx_process_cycle.c b/src/os/unix/ngx_process_cycle.c
+index df25f9d..bd259c1 100644
+--- a/src/os/unix/ngx_process_cycle.c
++++ b/src/os/unix/ngx_process_cycle.c
+@@ -442,6 +442,15 @@
+         return;
+     }
+ 
++    /* 0 is an illegal value and may result in a core dump later */
++    if (ccf->privileged_agent_connections == 0) {
++        ngx_log_error(NGX_LOG_ALERT, cycle->log, 0,
++                      "%ui worker_connection is not enough, "
++                      "privileged agent process cannot be spawned",
++                      ccf->privileged_agent_connections);
++        return;
++    }
++
+     ngx_spawn_process(cycle, ngx_privileged_agent_process_cycle,
+                       "privileged agent process", "privileged agent process",
+                       respawn ? NGX_PROCESS_JUST_RESPAWN : NGX_PROCESS_RESPAWN);