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authorEric Blake <eblake@redhat.com>2017-06-08 17:26:17 -0500
committerPaolo Bonzini <pbonzini@redhat.com>2017-06-15 11:04:05 +0200
commit0c9390d978cbf61e8f16c9f580fa96b305c43568 (patch)
tree9f1f1489689110cfd167a50c9f058795f789cea9 /nbd
parent457e03559dc57859eb12f993380ddeaeb73e9017 (diff)
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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>
Diffstat (limited to 'nbd')
-rw-r--r--nbd/server.c24
1 files changed, 15 insertions, 9 deletions
diff --git a/nbd/server.c b/nbd/server.c
index 49b55f6..f2b1aa4 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -81,7 +81,7 @@ static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
struct NBDClient {
int refcount;
- void (*close)(NBDClient *client);
+ void (*close_fn)(NBDClient *client, bool negotiated);
bool no_zeroes;
NBDExport *exp;
@@ -778,7 +778,7 @@ void nbd_client_put(NBDClient *client)
}
}
-static void client_close(NBDClient *client)
+static void client_close(NBDClient *client, bool negotiated)
{
if (client->closing) {
return;
@@ -793,8 +793,8 @@ 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);
}
}
@@ -975,7 +975,7 @@ 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_set_description(exp, NULL);
@@ -1337,7 +1337,7 @@ done:
out:
nbd_request_put(req);
- client_close(client);
+ client_close(client, true);
nbd_client_put(client);
}
@@ -1363,7 +1363,7 @@ 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;
}
@@ -1373,11 +1373,17 @@ 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);
@@ -1394,7 +1400,7 @@ void nbd_client_new(NBDExport *exp,
object_ref(OBJECT(client->sioc));
client->ioc = QIO_CHANNEL(sioc);
object_ref(OBJECT(client->ioc));
- client->close = close_fn;
+ client->close_fn = close_fn;
data->client = client;
data->co = qemu_coroutine_create(nbd_co_client_start, data);