[PATCH 2/2] pasta: Clean up waiting pasta child on failures

[David Gibson <david@gibson.dropbear.id.au>]

When pasta is invoked with a command rather than an existing namespace to
attach to, it spawns a child process to run a shell or other command.  We
create that process during conf(), since we need the namespace to exist for
much of our setup.  However, we don't want the specified command to run
until the pasta network interface is ready for use.  Therefore,
pasta_spawn_cmd() executing in the child waits before exec()ing.  main()
signals the child to continue with SIGUSR1 shortly before entering the
main forwarding loop.

This has the downside that if we exit due to any kind of failure between
conf() and the SIGUSR1, the child process will be around waiting
indefinitely.  The user must manually clean this up.

Make this cleaner, by having passt_exit() terminate the child, when called
during this window.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 passt.c | 1 +
 pasta.c | 2 ++
 pasta.h | 1 +
 util.c  | 5 +++++
 4 files changed, 9 insertions(+)

diff --git a/passt.c b/passt.c
index cf38822f..955c7091 100644
--- a/passt.c
+++ b/passt.c
@@ -431,6 +431,7 @@ int main(int argc, char **argv)
 	if (pasta_child_pid) {
 		kill(pasta_child_pid, SIGUSR1);
 		log_stderr = false;
+		pasta_child_signalled = true;
 	}
 
 	isolate_postfork(&c);
diff --git a/pasta.c b/pasta.c
index 5c693de1..8ac4511f 100644
--- a/pasta.c
+++ b/pasta.c
@@ -54,6 +54,8 @@
 
 /* PID of child, in case we created a namespace */
 int pasta_child_pid;
+/* Has the child been signalled to start a shell or command */
+bool pasta_child_signalled;
 
 /**
  * pasta_child_handler() - Exit once shell exits (if we started it), reap clones
diff --git a/pasta.h b/pasta.h
index 4b063d13..55028c74 100644
--- a/pasta.h
+++ b/pasta.h
@@ -7,6 +7,7 @@
 #define PASTA_H
 
 extern int pasta_child_pid;
+extern bool pasta_child_signalled;
 
 void pasta_open_ns(struct ctx *c, const char *netns);
 void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
diff --git a/util.c b/util.c
index e266c396..4744f09e 100644
--- a/util.c
+++ b/util.c
@@ -35,6 +35,7 @@
 #include "log.h"
 #include "pcap.h"
 #include "epoll_ctl.h"
+#include "pasta.h"
 #ifdef HAS_GETRANDOM
 #include <sys/random.h>
 #endif
@@ -1235,6 +1236,10 @@ void abort_with_msg(const char *fmt, ...)
  */
 void passt_exit(int status)
 {
+	/* If we're starting our own namespace, don't leave it in limbo */
+	if (pasta_child_pid && !pasta_child_signalled)
+		kill(pasta_child_pid, SIGTERM);
+
 	/* Make sure we don't leave the pcap file truncated */
 	if (pcap_fd != -1 && fsync(pcap_fd))
 		warn_perror("Failed to flush pcap file, it might be truncated");
-- 
2.52.0