File 0292-nbd-server-CVE-2024-7409-Drop-non-n.patch of Package qemu
From: Eric Blake <eblake@redhat.com>
Date: Thu, 8 Aug 2024 16:05:08 -0500
Subject: nbd/server: CVE-2024-7409: Drop non-negotiating clients (bsc#1229007,
bsc#1245423, CVE-2024-7409)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
A client that opens a socket but does not negotiate is merely hogging
qemu's resources (an open fd and a small amount of memory); and a
malicious client that can access the port where NBD is listening can
attempt a denial of service attack by intentionally opening and
abandoning lots of unfinished connections. The previous patch put a
default bound on the number of such ongoing connections, but once that
limit is hit, no more clients can connect (including legitimate ones).
The solution is to insist that clients complete handshake within a
reasonable time limit, defaulting to 10 seconds. A client that has
not successfully completed NBD_OPT_GO by then (including the case of
where the client didn't know TLS credentials to even reach the point
of NBD_OPT_GO) is wasting our time and does not deserve to stay
connected. Later patches will allow fine-tuning the limit away from
the default value (including disabling it for doing integration
testing of the handshake process itself).
Note that this patch in isolation actually makes it more likely to see
qemu SEGV after nbd-server-stop, as any client socket still connected
when the server shuts down will now be closed after 10 seconds rather
than at the client's whims. That will be addressed in the next patch.
For a demo of this patch in action:
$ qemu-nbd -f raw -r -t -e 10 file &
$ nbdsh --opt-mode -c '
H = list()
for i in range(20):
print(i)
H.insert(i, nbd.NBD())
H[i].set_opt_mode(True)
H[i].connect_uri("nbd://localhost")
'
$ kill $!
where later connections get to start progressing once earlier ones are
forcefully dropped for taking too long, rather than hanging.
Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-ID: <20240807174943.771624-13-eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
[eblake: rebase to changes earlier in series, reduce scope of timer]
Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit b9b72cb3ce15b693148bd09cef7e50110566d8a0)
References: bsc#1229007, bsc#1245423
References: CVE-2024-7409
Signed-off-by: Dario Faggioli <dfaggioli@suse.com>
Signed-off-by: Lin Ma <lma@suse.de>
---
nbd/server.c | 28 +++++++++++++++++++++++++++-
nbd/trace-events | 1 +
2 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/nbd/server.c b/nbd/server.c
index ab9134747d5e052967adf1c80250..80b242d83553544fbdd3306fc577 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -2385,22 +2385,48 @@ static void nbd_client_receive_next_request(NBDClient *client)
}
}
+static void nbd_handshake_timer_cb(void *opaque)
+{
+ QIOChannel *ioc = opaque;
+
+ trace_nbd_handshake_timer_cb();
+ qio_channel_shutdown(ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
+}
+
static coroutine_fn void nbd_co_client_start(void *opaque)
{
NBDClient *client = opaque;
Error *local_err = NULL;
+ QEMUTimer *handshake_timer = NULL;
qemu_co_mutex_init(&client->send_lock);
- /* TODO - utilize client->handshake_max_secs */
+ /*
+ * Create a timer to bound the time spent in negotiation. If the
+ * timer expires, it is likely nbd_negotiate will fail because the
+ * socket was shutdown.
+ */
+ if (client->handshake_max_secs > 0) {
+ handshake_timer = aio_timer_new(qemu_get_aio_context(),
+ QEMU_CLOCK_REALTIME,
+ SCALE_NS,
+ nbd_handshake_timer_cb,
+ client->sioc);
+ timer_mod(handshake_timer,
+ qemu_clock_get_ns(QEMU_CLOCK_REALTIME) +
+ client->handshake_max_secs * NANOSECONDS_PER_SECOND);
+ }
+
if (nbd_negotiate(client, &local_err)) {
if (local_err) {
error_report_err(local_err);
}
+ timer_free(handshake_timer);
client_close(client, false);
return;
}
+ timer_free(handshake_timer);
nbd_client_receive_next_request(client);
}
diff --git a/nbd/trace-events b/nbd/trace-events
index 5e1d4afe8e68479346226daf53cd..4df001910ad145583c6d2aa601f4 100644
--- a/nbd/trace-events
+++ b/nbd/trace-events
@@ -70,3 +70,4 @@ nbd_co_receive_request_decode_type(uint64_t handle, uint16_t type, const char *n
nbd_co_receive_request_payload_received(uint64_t handle, uint32_t len) "Payload received: handle = %" PRIu64 ", len = %" PRIu32
nbd_co_receive_request_cmd_write(uint32_t len) "Reading %" PRIu32 " byte(s)"
nbd_trip(void) "Reading request"
+nbd_handshake_timer_cb(void) "client took too long to negotiate"
