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qemu-linux-user
0241-nbd-Fix-regression-on-resiliency-to.patch
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File 0241-nbd-Fix-regression-on-resiliency-to.patch of Package qemu-linux-user
From: Eric Blake <eblake@redhat.com> Date: Thu, 8 Jun 2017 17:26:17 -0500 Subject: nbd: Fix regression on resiliency to port scan Back in qemu 2.5, qemu-nbd was immune to port probes (a transient server would not quit, regardless of how many probe connections came and went, until a connection actually negotiated). But we broke that in commit ee7d7aa when removing the return value to nbd_client_new(), although that patch also introduced a bug causing an assertion failure on a client that fails negotiation. We then made it worse during refactoring in commit 1a6245a (a segfault before we could even assert); the (masked) assertion was cleaned up in d3780c2 (still in 2.6), and just recently we finally fixed the segfault ("nbd: Fully intialize client in case of failed negotiation"). But that still means that ever since we added TLS support to qemu-nbd, we have been vulnerable to an ill-timed port-scan being able to cause a denial of service by taking down qemu-nbd before a real client has a chance to connect. Since negotiation is now handled asynchronously via coroutines, we no longer have a synchronous point of return by re-adding a return value to nbd_client_new(). So this patch instead wires things up to pass the negotiation status through the close_fn callback function. Simple test across two terminals: $ qemu-nbd -f raw -p 30001 file $ nmap 127.0.0.1 -p 30001 && \ qemu-io -c 'r 0 512' -f raw nbd://localhost:30001 Note that this patch does not change what constitutes successful negotiation (thus, a client must enter transmission phase before that client can be considered as a reason to terminate the server when the connection ends). Perhaps we may want to tweak things in a later patch to also treat a client that uses NBD_OPT_ABORT as being a 'successful' negotiation (the client correctly talked the NBD protocol, and informed us it was not going to use our export after all), but that's a discussion for another day. Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1451614 Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20170608222617.20376-1-eblake@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> (cherry picked from commit 0c9390d978cbf61e8f16c9f580fa96b305c43568) [FL: BSC#1043808 CVE-2017-9524] Signed-off-by: Fei Li <fli@suse.com> --- blockdev-nbd.c | 6 +++++- include/block/nbd.h | 2 +- nbd/server.c | 24 +++++++++++++++--------- qemu-nbd.c | 4 ++-- 4 files changed, 23 insertions(+), 13 deletions(-) diff --git a/blockdev-nbd.c b/blockdev-nbd.c index 12cae0ea720bd879f2abf92a78a5..37f693d47478b1407776c8db6e12 100644 --- a/blockdev-nbd.c +++ b/blockdev-nbd.c @@ -28,6 +28,10 @@ typedef struct NBDServerData { static NBDServerData *nbd_server; +static void nbd_blockdev_client_closed(NBDClient *client, bool ignored) +{ + nbd_client_put(client); +} static gboolean nbd_accept(QIOChannel *ioc, GIOCondition condition, gpointer opaque) @@ -46,7 +50,7 @@ static gboolean nbd_accept(QIOChannel *ioc, GIOCondition condition, nbd_client_new(NULL, cioc, nbd_server->tlscreds, NULL, - nbd_client_put); + nbd_blockdev_client_closed); object_unref(OBJECT(cioc)); return TRUE; } diff --git a/include/block/nbd.h b/include/block/nbd.h index fde4421e5d55e45ae9e9e74d7602..2304da5685e83fde87edccc4a5b2 100644 --- a/include/block/nbd.h +++ b/include/block/nbd.h @@ -114,7 +114,7 @@ void nbd_client_new(NBDExport *exp, QIOChannelSocket *sioc, QCryptoTLSCreds *tlscreds, const char *tlsaclname, - void (*close)(NBDClient *)); + void (*close_fn)(NBDClient *, bool)); void nbd_client_get(NBDClient *client); void nbd_client_put(NBDClient *client); diff --git a/nbd/server.c b/nbd/server.c index 493e8421b7f1e853ccdccef2b79a..a9419428733e9174e5fd88b24c43 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -75,7 +75,7 @@ static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports); struct NBDClient { int refcount; - void (*close)(NBDClient *client); + void (*close_fn)(NBDClient *client, bool negotiated); NBDExport *exp; QCryptoTLSCreds *tlscreds; @@ -728,7 +728,7 @@ void nbd_client_put(NBDClient *client) } } -static void client_close(NBDClient *client) +static void client_close(NBDClient *client, bool negotiated) { if (client->closing) { return; @@ -743,8 +743,8 @@ static void client_close(NBDClient *client) NULL); /* Also tell the client, so that they release their reference. */ - if (client->close) { - client->close(client); + if (client->close_fn) { + client->close_fn(client, negotiated); } } @@ -890,7 +890,7 @@ void nbd_export_close(NBDExport *exp) nbd_export_get(exp); QTAILQ_FOREACH_SAFE(client, &exp->clients, next, next) { - client_close(client); + client_close(client, true); } nbd_export_set_name(exp, NULL); nbd_export_put(exp); @@ -1195,7 +1195,7 @@ done: out: nbd_request_put(req); - client_close(client); + client_close(client, true); } static void nbd_read(void *opaque) @@ -1262,7 +1262,7 @@ static coroutine_fn void nbd_co_client_start(void *opaque) qemu_co_mutex_init(&client->send_lock); if (nbd_negotiate(data)) { - client_close(client); + client_close(client, false); goto out; } @@ -1272,11 +1272,17 @@ out: g_free(data); } +/* + * Create a new client listener on the given export @exp, using the + * given channel @sioc. Begin servicing it in a coroutine. When the + * connection closes, call @close_fn with an indication of whether the + * client completed negotiation. + */ void nbd_client_new(NBDExport *exp, QIOChannelSocket *sioc, QCryptoTLSCreds *tlscreds, const char *tlsaclname, - void (*close_fn)(NBDClient *)) + void (*close_fn)(NBDClient *, bool)) { NBDClient *client; NBDClientNewData *data = g_new(NBDClientNewData, 1); @@ -1294,7 +1300,7 @@ void nbd_client_new(NBDExport *exp, client->ioc = QIO_CHANNEL(sioc); object_ref(OBJECT(client->ioc)); client->can_read = true; - client->close = close_fn; + client->close_fn = close_fn; data->client = client; data->co = qemu_coroutine_create(nbd_co_client_start); diff --git a/qemu-nbd.c b/qemu-nbd.c index 946ea9d6c7168258d064d6ea7dd1..0b5e8e5a261666688ac4cf7e47ac 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -320,10 +320,10 @@ static void nbd_export_closed(NBDExport *exp) static void nbd_update_server_watch(void); -static void nbd_client_closed(NBDClient *client) +static void nbd_client_closed(NBDClient *client, bool negotiated) { nb_fds--; - if (nb_fds == 0 && !persistent && state == RUNNING) { + if (negotiated && nb_fds == 0 && !persistent && state == RUNNING) { state = TERMINATE; } nbd_update_server_watch();
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