pasta: Add fallback timer mechanism to check if namespace is gone

We don't know how frequently this happens, but hitting
fs.inotify.max_user_watches or similar sysctl limits is definitely
not out of question, and Paul mentioned that, for example, Podman's
CI environments hit similar issues in the past.

Introduce a fallback mechanism based on a timer file descriptor: we
grab the directory handle at startup, and we can then use openat(),
triggered periodically, to check if the (network) namespace directory
still exists. If openat() fails at some point, exit.

Link: https://github.com/containers/podman/pull/21563#issuecomment-1943505707
Reported-by: Paul Holzinger <pholzing@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 19 insertions, 15 deletions

diff --git a/passt.c b/passt.c
index aaa8e58..a90568f 100644
--- a/passt.c
+++ b/passt.c
@@ -61,17 +61,18 @@
 char pkt_buf[PKT_BUF_BYTES]	__attribute__ ((aligned(PAGE_SIZE)));
 
 char *epoll_type_str[] = {
-	[EPOLL_TYPE_TCP]	= "connected TCP socket",
-	[EPOLL_TYPE_TCP_SPLICE]	= "connected spliced TCP socket",
-	[EPOLL_TYPE_TCP_LISTEN]	= "listening TCP socket",
-	[EPOLL_TYPE_TCP_TIMER]	= "TCP timer",
-	[EPOLL_TYPE_UDP]	= "UDP socket",
-	[EPOLL_TYPE_ICMP]	= "ICMP socket",
-	[EPOLL_TYPE_ICMPV6]	= "ICMPv6 socket",
-	[EPOLL_TYPE_NSQUIT]	= "namespace inotify",
-	[EPOLL_TYPE_TAP_PASTA]	= "/dev/net/tun device",
-	[EPOLL_TYPE_TAP_PASST]	= "connected qemu socket",
-	[EPOLL_TYPE_TAP_LISTEN]	= "listening qemu socket",
+	[EPOLL_TYPE_TCP]		= "connected TCP socket",
+	[EPOLL_TYPE_TCP_SPLICE]		= "connected spliced TCP socket",
+	[EPOLL_TYPE_TCP_LISTEN]		= "listening TCP socket",
+	[EPOLL_TYPE_TCP_TIMER]		= "TCP timer",
+	[EPOLL_TYPE_UDP]		= "UDP socket",
+	[EPOLL_TYPE_ICMP]		= "ICMP socket",
+	[EPOLL_TYPE_ICMPV6]		= "ICMPv6 socket",
+	[EPOLL_TYPE_NSQUIT_INOTIFY]	= "namespace inotify watch",
+	[EPOLL_TYPE_NSQUIT_TIMER]	= "namespace timer watch",
+	[EPOLL_TYPE_TAP_PASTA]		= "/dev/net/tun device",
+	[EPOLL_TYPE_TAP_PASST]		= "connected qemu socket",
+	[EPOLL_TYPE_TAP_LISTEN]		= "listening qemu socket",
 };
 static_assert(ARRAY_SIZE(epoll_type_str) == EPOLL_NUM_TYPES,
 	      "epoll_type_str[] doesn't match enum epoll_type");
@@ -201,7 +202,7 @@ void exit_handler(int signal)
  */
 int main(int argc, char **argv)
 {
-	int nfds, i, devnull_fd = -1, pidfile_fd = -1, quit_fd;
+	int nfds, i, devnull_fd = -1, pidfile_fd = -1;
 	struct epoll_event events[EPOLL_EVENTS];
 	char *log_name, argv0[PATH_MAX], *name;
 	struct ctx c = { 0 };
@@ -274,7 +275,7 @@ int main(int argc, char **argv)
 	if (c.force_stderr || isatty(fileno(stdout)))
 		__openlog(log_name, LOG_PERROR, LOG_DAEMON);
 
-	quit_fd = pasta_netns_quit_init(&c);
+	pasta_netns_quit_init(&c);
 
 	tap_sock_init(&c);
 
@@ -370,8 +371,11 @@ loop:
 		case EPOLL_TYPE_TAP_LISTEN:
 			tap_listen_handler(&c, eventmask);
 			break;
-		case EPOLL_TYPE_NSQUIT:
-			pasta_netns_quit_handler(&c, quit_fd);
+		case EPOLL_TYPE_NSQUIT_INOTIFY:
+			pasta_netns_quit_inotify_handler(&c, ref.fd);
+			break;
+		case EPOLL_TYPE_NSQUIT_TIMER:
+			pasta_netns_quit_timer_handler(&c, ref);
 			break;
 		case EPOLL_TYPE_TCP:
 			tcp_sock_handler(&c, ref, eventmask);