From: Eric Blake <eblake@redhat.com>
Date: Wed, 7 Aug 2024 08:50:01 -0500
Subject: nbd/server: Plumb in new args to nbd_client_add() (bsc#1229007,
 CVE-2024-7409)
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Upcoming patches to fix a CVE need to track an opaque pointer passed
in by the owner of a client object, as well as request for a time
limit on how fast negotiation must complete.  Prepare for that by
changing the signature of nbd_client_new() and adding an accessor to
get at the opaque pointer, although for now the two servers
(qemu-nbd.c and blockdev-nbd.c) do not change behavior even though
they pass in a new default timeout value.

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-ID: <20240807174943.771624-11-eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
[eblake: s/LIMIT/MAX_SECS/ as suggested by Dan]
Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit fb1c2aaa981e0a2fa6362c9985f1296b74f055ac)
References: bsc#1229007
References: CVE-2024-7409
Signed-off-by: Dario Faggioli <dfaggioli@suse.com>
---
 blockdev-nbd.c      |  6 ++++--
 include/block/nbd.h | 11 ++++++++++-
 nbd/server.c        | 20 +++++++++++++++++---
 qemu-nbd.c          |  4 +++-
 4 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 8c20baa4a4b93abd60f1912da81b..bd56b367e06bb9a8f8580ff52f6c 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -36,8 +36,10 @@ static void nbd_accept(QIONetListener *listener, QIOChannelSocket *cioc,
                        gpointer opaque)
 {
     qio_channel_set_name(QIO_CHANNEL(cioc), "nbd-server");
-    nbd_client_new(cioc, nbd_server->tlscreds, nbd_server->tlsauthz,
-                   nbd_blockdev_client_closed);
+    /* TODO - expose handshake timeout as QMP option */
+    nbd_client_new(cioc, NBD_DEFAULT_HANDSHAKE_MAX_SECS,
+                   nbd_server->tlscreds, nbd_server->tlsauthz,
+                   nbd_blockdev_client_closed, NULL);
 }
 
 
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 7f46932d80f1b4f3dcaa63c211d6..ccc9cb9d3ca4e137c7f345712ffe 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -25,6 +25,12 @@
 #include "crypto/tlscreds.h"
 #include "qapi/error.h"
 
+/*
+ * NBD_DEFAULT_HANDSHAKE_MAX_SECS: Number of seconds in which client must
+ * succeed at NBD_OPT_GO before being forcefully dropped as too slow.
+ */
+#define NBD_DEFAULT_HANDSHAKE_MAX_SECS 10
+
 /* Handshake phase structs - this struct is passed on the wire */
 
 struct NBDOption {
@@ -345,9 +351,12 @@ NBDExport *nbd_export_find(const char *name);
 void nbd_export_close_all(void);
 
 void nbd_client_new(QIOChannelSocket *sioc,
+                    uint32_t handshake_max_secs,
                     QCryptoTLSCreds *tlscreds,
                     const char *tlsauthz,
-                    void (*close_fn)(NBDClient *, bool));
+                    void (*close_fn)(NBDClient *, bool),
+                    void *owner);
+void *nbd_client_owner(NBDClient *client);
 void nbd_client_get(NBDClient *client);
 void nbd_client_put(NBDClient *client);
 
diff --git a/nbd/server.c b/nbd/server.c
index 3703aac0f0fb9a47cb26af98e8fe..7e354499a28ce4734c0f5982fd26 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -117,10 +117,12 @@ typedef struct NBDExportMetaContexts {
 struct NBDClient {
     int refcount;
     void (*close_fn)(NBDClient *client, bool negotiated);
+    void *owner;
 
     NBDExport *exp;
     QCryptoTLSCreds *tlscreds;
     char *tlsauthz;
+    uint32_t handshake_max_secs;
     QIOChannelSocket *sioc; /* The underlying data channel */
     QIOChannel *ioc; /* The current I/O channel which may differ (eg TLS) */
 
@@ -2521,6 +2523,7 @@ static coroutine_fn void nbd_co_client_start(void *opaque)
 
     qemu_co_mutex_init(&client->send_lock);
 
+    /* TODO - utilize client->handshake_max_secs */
     if (nbd_negotiate(client, &local_err)) {
         if (local_err) {
             error_report_err(local_err);
@@ -2533,14 +2536,17 @@ static coroutine_fn void nbd_co_client_start(void *opaque)
 }
 
 /*
- * Create a new client listener using the given channel @sioc.
+ * Create a new client listener using the given channel @sioc and @owner.
  * Begin servicing it in a coroutine.  When the connection closes, call
- * @close_fn with an indication of whether the client completed negotiation.
+ * @close_fn with an indication of whether the client completed negotiation
+ * within @handshake_max_secs seconds (0 for unbounded).
  */
 void nbd_client_new(QIOChannelSocket *sioc,
+                    uint32_t handshake_max_secs,
                     QCryptoTLSCreds *tlscreds,
                     const char *tlsauthz,
-                    void (*close_fn)(NBDClient *, bool))
+                    void (*close_fn)(NBDClient *, bool),
+                    void *owner)
 {
     NBDClient *client;
     Coroutine *co;
@@ -2552,12 +2558,20 @@ void nbd_client_new(QIOChannelSocket *sioc,
         object_ref(OBJECT(client->tlscreds));
     }
     client->tlsauthz = g_strdup(tlsauthz);
+    client->handshake_max_secs = handshake_max_secs;
     client->sioc = sioc;
     object_ref(OBJECT(client->sioc));
     client->ioc = QIO_CHANNEL(sioc);
     object_ref(OBJECT(client->ioc));
     client->close_fn = close_fn;
+    client->owner = owner;
 
     co = qemu_coroutine_create(nbd_co_client_start, client);
     qemu_coroutine_enter(co);
 }
+
+void *
+nbd_client_owner(NBDClient *client)
+{
+    return client->owner;
+}
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 684615934dc9de1f2814f115f1cc..9775b7ede08dfe326790060096ac 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -449,7 +449,9 @@ static void nbd_accept(QIONetListener *listener, QIOChannelSocket *cioc,
 
     nb_fds++;
     nbd_update_server_watch();
-    nbd_client_new(cioc, tlscreds, tlsauthz, nbd_client_closed);
+    /* TODO - expose handshake timeout as command line option */
+    nbd_client_new(cioc, NBD_DEFAULT_HANDSHAKE_MAX_SECS,
+                   tlscreds, tlsauthz, nbd_client_closed, NULL);
 }
 
 static void nbd_update_server_watch(void)
