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server: correctly adjudicate collision bind() of specific port

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On Linux (at least) SO_REUSEADDR, which allows a new listener to
bind while an existing sock is in FIN-WAIT.  Apparently this allows
any number of sockets to bind(), but only when listen() to succeed.

Further, on Linux there is a known documented race condition which
can result in all listen() failing.  It isn't clear how to handle
this case without a potentially infinite loop, so ignore it.
If this happens, then eg. no PVA server will get port 5075.

So when probing for another listener, it is necessary to enter the
listening state.  When this fails, the socket is no longer usable
for another bind(), so it is necessary to allocate another for the
next attempt.
This commit is contained in:
Michael Davidsaver
2024-08-14 17:30:12 -07:00
parent 5fa743d4c8
commit a3a685ba2b
1 changed files with 29 additions and 19 deletions
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src/serverconn.cpp
+29 -19
View File
@@ -408,18 +408,40 @@ ServIface::ServIface(const SockAddr &addr, server::Server::Pvt *server, bool fal
server->acceptor_loop.assertInLoop();
auto orig_port = bind_addr.port();
sock = evsocket(bind_addr.family(), SOCK_STREAM, 0);
if(evutil_make_listen_socket_reuseable(sock.sock))
log_warn_printf(connsetup, "Unable to make socket reusable%s", "\n");
// try to bind to requested port, then fallback to a random port
while(true) {
sock = evsocket(bind_addr.family(), SOCK_STREAM, 0);
if(evutil_make_listen_socket_reuseable(sock.sock))
log_warn_printf(connsetup, "Unable to make socket reusable%s", "\n");
try {
sock.bind(bind_addr);
// semantics of SO_REUSEADDR on *nix allow multiple bind() to success.
// however, only one listen() will succeed
// added in libevent 2.1.1
#ifndef LEV_OPT_DISABLED
# define LEV_OPT_DISABLED 0
#endif
const int backlog = 4;
auto list(evconnlistener_new(server->acceptor_loop.base, onConnS, this, LEV_OPT_DISABLED|LEV_OPT_CLOSE_ON_EXEC, backlog, sock.sock));
if(!list) {
int err = evutil_socket_geterror(sock);
throw std::system_error(err, std::system_category());
}
listener = evlisten(__FILE__, __LINE__, list);
if(!LEV_OPT_DISABLED)
evconnlistener_disable(listener.get());
} catch(std::system_error& e) {
if(fallback && e.code().value()==SOCK_EADDRINUSE) {
log_debug_printf(connsetup, "Address %s in use\n", bind_addr.tostring().c_str());
if(fallback && (e.code().value()==SOCK_EADDRINUSE || e.code().value()==SOCK_EACCES)) {
log_debug_printf(connsetup, "Address %s in use or not permitted: %s\n",
bind_addr.tostring().c_str(),
e.what());
bind_addr.setPort(0);
fallback = false;
continue;
@@ -438,18 +460,6 @@ ServIface::ServIface(const SockAddr &addr, server::Server::Pvt *server, bool fal
if(orig_port && bind_addr.port() != orig_port) {
log_warn_printf(connsetup, "Server unable to bind port %u, falling back to %s\n", orig_port, name.c_str());
}
// added in libevent 2.1.1
#ifndef LEV_OPT_DISABLED
# define LEV_OPT_DISABLED 0
#endif
const int backlog = 4;
listener = evlisten(__FILE__, __LINE__,
evconnlistener_new(server->acceptor_loop.base, onConnS, this, LEV_OPT_DISABLED|LEV_OPT_CLOSE_ON_EXEC, backlog, sock.sock));
if(!LEV_OPT_DISABLED)
evconnlistener_disable(listener.get());
}
void ServIface::onConnS(struct evconnlistener *listener, evutil_socket_t sock, struct sockaddr *peer, int socklen, void *raw)