From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: [PATCH qemu-traditional] qemu: Fix race condition when binding ports Date: Mon, 9 Dec 2013 13:10:52 +0000 Message-ID: <1386594652-6953-1-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Xen-devel Cc: George Dunlap , Andrew Cooper , Ian Jackson , Ian Campbell , Stefano Stabellini List-Id: xen-devel@lists.xenproject.org Two Qemus can race to bind the same VNC port. It is valid for multiple listen()s on the same socket to succeed, but only the first bind() will succeed. In the case that two Qemus are racing, the second one will fail with an EADDRINUSE, and bail with a fatal error which renders the domain functionally useless. In the case that bind() fails with EADDRINUSE, rebind the socket again and try for the next port. Signed-off-by: Andrew Cooper CC: Ian Campbell CC: Ian Jackson CC: Stefano Stabellini CC: George Dunlap --- This fix has been in XenServer for two and a half years --- qemu-sockets.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-) diff --git a/qemu-sockets.c b/qemu-sockets.c index 9b9fa77..e54f6ad 100644 --- a/qemu-sockets.c +++ b/qemu-sockets.c @@ -163,6 +163,7 @@ int inet_listen(const char *str, char *ostr, int olen, /* create socket + bind */ for (e = res; e != NULL; e = e->ai_next) { + rebind: getnameinfo((struct sockaddr*)e->ai_addr,e->ai_addrlen, uaddr,INET6_ADDRSTRLEN,uport,32, NI_NUMERICHOST | NI_NUMERICSERV); @@ -186,7 +187,20 @@ int inet_listen(const char *str, char *ostr, int olen, if (sockets_debug) fprintf(stderr,"%s: bind(%s,%s,%d): OK\n", __FUNCTION__, inet_strfamily(e->ai_family), uaddr, inet_getport(e)); - goto listen; + if (listen(slisten,1) == 0) { + goto listened; + } else { + int err = errno; + + perror("listen"); + closesocket(slisten); + + if (err == EADDRINUSE) + goto rebind; + freeaddrinfo(res); + return -1; + } + } try_next = to && (inet_getport(e) <= to + port_offset); if (!try_next || sockets_debug) @@ -205,12 +219,7 @@ int inet_listen(const char *str, char *ostr, int olen, freeaddrinfo(res); return -1; -listen: - if (listen(slisten,1) != 0) { - perror("listen"); - closesocket(slisten); - return -1; - } +listened: if (ostr) { if (e->ai_family == PF_INET6) { snprintf(ostr, olen, "[%s]:%d%s", uaddr, -- 1.7.10.4