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[Qemu-devel] [PULL v1 03/11] sockets: Handle race condition between bind
From: |
Daniel P. Berrange |
Subject: |
[Qemu-devel] [PULL v1 03/11] sockets: Handle race condition between binds to the same port |
Date: |
Mon, 16 Oct 2017 21:16:42 +0100 |
From: Knut Omang <address@hidden>
If an offset of ports is specified to the inet_listen_saddr function(),
and two or more processes tries to bind from these ports at the same time,
occasionally more than one process may be able to bind to the same
port. The condition is detected by listen() but too late to avoid a failure.
This function is called by socket_listen() and used
by all socket listening code in QEMU, so all cases where any form of dynamic
port selection is used should be subject to this issue.
Add code to close and re-establish the socket when this
condition is observed, hiding the race condition from the user.
Also clean up some issues with error handling to allow more
accurate reporting of the cause of an error.
This has been developed and tested by means of the
test-listen unit test in the previous commit.
Enable the test for make check now that it passes.
Reviewed-by: Bhavesh Davda <address@hidden>
Reviewed-by: Yuval Shaia <address@hidden>
Reviewed-by: Girish Moodalbail <address@hidden>
Signed-off-by: Knut Omang <address@hidden>
Reviewed-by: Daniel P. Berrange <address@hidden>
Signed-off-by: Daniel P. Berrange <address@hidden>
---
util/qemu-sockets.c | 58 +++++++++++++++++++++++++++++++++++++----------------
1 file changed, 41 insertions(+), 17 deletions(-)
diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
index 65f6dcd5ef..b47fb45885 100644
--- a/util/qemu-sockets.c
+++ b/util/qemu-sockets.c
@@ -206,7 +206,10 @@ static int inet_listen_saddr(InetSocketAddress *saddr,
char port[33];
char uaddr[INET6_ADDRSTRLEN+1];
char uport[33];
- int slisten, rc, port_min, port_max, p;
+ int rc, port_min, port_max, p;
+ int slisten = 0;
+ int saved_errno = 0;
+ bool socket_created = false;
Error *err = NULL;
memset(&ai,0, sizeof(ai));
@@ -258,7 +261,7 @@ static int inet_listen_saddr(InetSocketAddress *saddr,
return -1;
}
- /* create socket + bind */
+ /* create socket + bind/listen */
for (e = res; e != NULL; e = e->ai_next) {
getnameinfo((struct sockaddr*)e->ai_addr,e->ai_addrlen,
uaddr,INET6_ADDRSTRLEN,uport,32,
@@ -266,37 +269,58 @@ static int inet_listen_saddr(InetSocketAddress *saddr,
slisten = create_fast_reuse_socket(e);
if (slisten < 0) {
- if (!e->ai_next) {
- error_setg_errno(errp, errno, "Failed to create socket");
- }
continue;
}
+ socket_created = true;
port_min = inet_getport(e);
port_max = saddr->has_to ? saddr->to + port_offset : port_min;
for (p = port_min; p <= port_max; p++) {
inet_setport(e, p);
- if (try_bind(slisten, saddr, e) >= 0) {
- goto listen;
- }
- if (p == port_max) {
- if (!e->ai_next) {
+ rc = try_bind(slisten, saddr, e);
+ if (rc) {
+ if (errno == EADDRINUSE) {
+ continue;
+ } else {
error_setg_errno(errp, errno, "Failed to bind socket");
+ goto listen_failed;
}
}
+ if (!listen(slisten, 1)) {
+ goto listen_ok;
+ }
+ if (errno != EADDRINUSE) {
+ error_setg_errno(errp, errno, "Failed to listen on socket");
+ goto listen_failed;
+ }
+ /* Someone else managed to bind to the same port and beat us
+ * to listen on it! Socket semantics does not allow us to
+ * recover from this situation, so we need to recreate the
+ * socket to allow bind attempts for subsequent ports:
+ */
+ closesocket(slisten);
+ slisten = create_fast_reuse_socket(e);
+ if (slisten < 0) {
+ error_setg_errno(errp, errno,
+ "Failed to recreate failed listening socket");
+ goto listen_failed;
+ }
}
+ }
+ error_setg_errno(errp, errno,
+ socket_created ?
+ "Failed to find an available port" :
+ "Failed to create a socket");
+listen_failed:
+ saved_errno = errno;
+ if (slisten >= 0) {
closesocket(slisten);
}
freeaddrinfo(res);
+ errno = saved_errno;
return -1;
-listen:
- if (listen(slisten,1) != 0) {
- error_setg_errno(errp, errno, "Failed to listen on socket");
- closesocket(slisten);
- freeaddrinfo(res);
- return -1;
- }
+listen_ok:
if (update_addr) {
g_free(saddr->host);
saddr->host = g_strdup(uaddr);
--
2.13.5
- [Qemu-devel] [PULL v1 00/11] Merge QIO 2017-10-16, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 03/11] sockets: Handle race condition between binds to the same port,
Daniel P. Berrange <=
- [Qemu-devel] [PULL v1 02/11] sockets: factor out create_fast_reuse_socket, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 01/11] sockets: factor out a new try_bind() function, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 04/11] io: monitor encoutput buffer size from websocket GSource, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 06/11] io: get rid of qio_channel_websock_encode helper method, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 05/11] io: simplify websocket ping reply handling, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 09/11] io: cope with websock 'Connection' header having multiple values, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 08/11] io: get rid of bounce buffering in websock write path, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 07/11] io: pass a struct iovec into qio_channel_websock_encode, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 10/11] io: add trace points for websocket HTTP protocol headers, Daniel P. Berrange, 2017/10/16
- [Qemu-devel] [PULL v1 11/11] io: fix mem leak in websock error path, Daniel P. Berrange, 2017/10/16