capture-sync: Fix deadlock with lots of interfaces.

This code is still fragile, it should not deadlock even if there
is too much to read, but this at least hacks around the problem.

To avoid huge stacks, allocate the buffer on the heap.

Fixes wireshark hang with about 50 interfaces...

Signed-off-by: Ben Greear <greearb@candelatech.com>

capture/capture_sync.c

@@ -1034,7 +1034,7 @@ sync_pipe_run_command_actual(char **argv, char **data, char **primary_msg,
     GIOChannel *sync_pipe_read_io;
     ws_process_id fork_child;
     char *wait_msg;
-    char buffer[PIPE_BUF_SIZE+1] = {0};
+    char *buffer = g_malloc(PIPE_BUF_SIZE + 1);
     ssize_t nread;
     char indicator;
     int32_t exec_errno = 0;
@@ -1052,6 +1052,7 @@ sync_pipe_run_command_actual(char **argv, char **data, char **primary_msg,
         *primary_msg = msg;
         *secondary_msg = NULL;
         *data = NULL;
+        g_free(buffer);
         return -1;
     }
 
@@ -1097,6 +1098,7 @@ sync_pipe_run_command_actual(char **argv, char **data, char **primary_msg,
             }
             *secondary_msg = NULL;
             *data = NULL;
+            g_free(buffer);
 
             return -1;
         }
@@ -1242,6 +1244,7 @@ sync_pipe_run_command_actual(char **argv, char **data, char **primary_msg,
         }
     } while (indicator != SP_SUCCESS && ret != -1);
 
+    g_free(buffer);
     return ret;
 }
 
@@ -1471,7 +1474,7 @@ sync_interface_stats_open(int *data_read_fd, ws_process_id *fork_child, char **d
     int ret;
     GIOChannel *message_read_io;
     char *wait_msg;
-    char buffer[PIPE_BUF_SIZE+1] = {0};
+    char *buffer = g_malloc(PIPE_BUF_SIZE + 1);
     ssize_t nread;
     char indicator;
     int32_t exec_errno = 0;
@@ -1487,6 +1490,7 @@ sync_interface_stats_open(int *data_read_fd, ws_process_id *fork_child, char **d
 
     if (!argv) {
         *msg = g_strdup("We don't know where to find dumpcap.");
+        g_free(buffer);
         return -1;
     }
 
@@ -1504,6 +1508,7 @@ sync_interface_stats_open(int *data_read_fd, ws_process_id *fork_child, char **d
     argv = sync_pipe_add_arg(argv, &argc, "--signal-pipe");
     ret = create_dummy_signal_pipe(msg);
     if (ret == -1) {
+        g_free(buffer);
         return -1;
     }
     argv = sync_pipe_add_arg(argv, &argc, dummy_control_id);
@@ -1512,6 +1517,7 @@ sync_interface_stats_open(int *data_read_fd, ws_process_id *fork_child, char **d
     ret = sync_pipe_open_command(argv, data_read_fd, &message_read_io, NULL,
                                  fork_child, NULL, msg, update_cb);
     if (ret == -1) {
+        g_free(buffer);
         return -1;
     }
 
@@ -1556,6 +1562,7 @@ sync_interface_stats_open(int *data_read_fd, ws_process_id *fork_child, char **d
                     *msg = combined_msg;
                 }
             }
+            g_free(buffer);
             return -1;
         }
 
@@ -1626,6 +1633,7 @@ sync_interface_stats_open(int *data_read_fd, ws_process_id *fork_child, char **d
                 *msg = g_strdup(primary_msg_text);
                 ret = -1;
             }
+            g_free(buffer);
             return ret;
 
         case SP_LOG_MSG:
@@ -1674,6 +1682,7 @@ sync_interface_stats_open(int *data_read_fd, ws_process_id *fork_child, char **d
         }
     } while (indicator != SP_SUCCESS && ret != -1);
 
+    g_free(buffer);
     return ret;
 }
 
@@ -1859,7 +1868,7 @@ static gboolean
 sync_pipe_input_cb(GIOChannel *pipe_io, capture_session *cap_session)
 {
     int  ret;
-    char buffer[SP_MAX_MSG_LEN+1] = {0};
+    char *buffer = g_malloc(SP_MAX_MSG_LEN + 1);
     ssize_t nread;
     char indicator;
     int32_t exec_errno = 0;
@@ -1918,6 +1927,7 @@ sync_pipe_input_cb(GIOChannel *pipe_io, capture_session *cap_session)
         } else {
             extcap_request_stop(cap_session);
         }
+        g_free(buffer);
         return false;
     }
 
@@ -1944,6 +1954,7 @@ sync_pipe_input_cb(GIOChannel *pipe_io, capture_session *cap_session)
                "standard output", as the capture file. */
             sync_pipe_stop(cap_session);
             cap_session->closed(cap_session, NULL);
+            g_free(buffer);
             return false;
         }
         break;
@@ -2019,6 +2030,7 @@ sync_pipe_input_cb(GIOChannel *pipe_io, capture_session *cap_session)
         break;
     }
 
+    g_free(buffer);
     return true;
 }
 

sync_pipe.h

@@ -30,7 +30,7 @@
  * 4096 is a typical PIPE_BUF size for atomic writes, but we should have
  * only one writer and one reader so that shouldn't be an issue.
  */
-#define SP_MAX_MSG_LEN  24572
+#define SP_MAX_MSG_LEN  (512 * 1000)
 
 /*
  * Indications sent out on the sync pipe (from child to parent).