[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v4 4/4] sockets: Handle race condition between b
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [PATCH v4 4/4] sockets: Handle race condition between binds to the same port |
Date: |
Mon, 26 Jun 2017 11:34:02 +0100 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Fri, Jun 23, 2017 at 12:31:08PM +0200, Knut Omang wrote:
> 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.
>
> 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.
>
> Signed-off-by: Knut Omang <address@hidden>
> Reviewed-by: Bhavesh Davda <address@hidden>
> Reviewed-by: Yuval Shaia <address@hidden>
> Reviewed-by: Girish Moodalbail <address@hidden>
> ---
> tests/Makefile.include | 2 +-
> util/qemu-sockets.c | 68 ++++++++++++++++++++++++++++++++-----------
> 2 files changed, 53 insertions(+), 17 deletions(-)
>
> diff --git a/tests/Makefile.include b/tests/Makefile.include
> index 22bb97e..c38f94e 100644
> --- a/tests/Makefile.include
> +++ b/tests/Makefile.include
> @@ -127,7 +127,7 @@ check-unit-y += tests/test-bufferiszero$(EXESUF)
> gcov-files-check-bufferiszero-y = util/bufferiszero.c
> check-unit-y += tests/test-uuid$(EXESUF)
> check-unit-y += tests/ptimer-test$(EXESUF)
> -#check-unit-y += tests/test-listen$(EXESUF)
> +check-unit-y += tests/test-listen$(EXESUF)
> gcov-files-ptimer-test-y = hw/core/ptimer.c
> check-unit-y += tests/test-qapi-util$(EXESUF)
> gcov-files-test-qapi-util-y = qapi/qapi-util.c
> diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
> index 48b9319..7b118b4 100644
> --- a/util/qemu-sockets.c
> +++ b/util/qemu-sockets.c
> @@ -201,6 +201,42 @@ static int try_bind(int socket, InetSocketAddress
> *saddr, struct addrinfo *e)
> #endif
> }
>
> +static int try_bind_listen(int *socket, InetSocketAddress *saddr,
> + struct addrinfo *e, int port, Error **errp)
> +{
> + int s = *socket;
> + int ret;
> +
> + inet_setport(e, port);
> + ret = try_bind(s, saddr, e);
> + if (ret) {
> + if (errno != EADDRINUSE) {
> + error_setg_errno(errp, errno, "Failed to bind socket");
> + }
> + return errno;
> + }
> + if (listen(s, 1) == 0) {
> + return 0;
> + }
> + if (errno == EADDRINUSE) {
> + /* We got to bind the socket to a port but someone else managed
> + * to bind to the same port and beat us to listen on it!
> + * Recreate the socket and return EADDRINUSE to preserve the
> + * expected state by the caller:
> + */
> + closesocket(s);
> + s = create_fast_reuse_socket(e, errp);
This usage scenario for create_fast_reuse_socket() makes its error
reporting behaviour even more wrong. Recall that create_fast_reuse_socket
is reporting an error if e->ai_next is NULL, which is a way of determining
this is the last call to create_fast_reuse_socket in the loop. That
assumption is violated though now that we're calling the method from
inside the inner loop. Even when e->ai_next is NULL, we may be calling
create_fast_reuse_socket many many times due to the port 'to' range.
> + if (s < 0) {
> + return errno;
> + }
> + *socket = s;
> + errno = EADDRINUSE;
> + return errno;
> + }
> + error_setg_errno(errp, errno, "Failed to listen on socket");
> + return errno;
> +}
This method is both preserving the global errno, and returning the
global errno. The caller expects global errno to be preserved, so
I think we can just return '-1' from this method.
> +
> static int inet_listen_saddr(InetSocketAddress *saddr,
> int port_offset,
> bool update_addr,
> @@ -210,7 +246,9 @@ 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;
> Error *err = NULL;
>
> memset(&ai,0, sizeof(ai));
> @@ -276,28 +314,26 @@ static int inet_listen_saddr(InetSocketAddress *saddr,
> 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) {
> - error_setg_errno(errp, errno, "Failed to bind socket");
> - }
> + int eno = try_bind_listen(&slisten, saddr, e, p, &err);
> + if (!eno) {
> + goto listen_ok;
> + } else if (eno != EADDRINUSE) {
> + goto listen_failed;
> }
> }
> + }
> + error_setg_errno(errp, errno, "Failed to find available port");
> +
> +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);
> --
> git-series 0.9.1
Regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|