On Mon, Aug 05, 2024 at 09:21:36PM -0500, Eric Blake wrote:
> Since an NBD server may be long-living, serving clients that
> repeatedly connect and disconnect, it can be more efficient to clean
> up after each client disconnects, rather than storing a list of
> resources to clean up when the server exits. Rewrite the list of
> known clients to be double-linked so that we can get O(1) deletion to
> keep the list pruned to size as clients exit. This in turn requires
> each client to track an opaque pointer of owner information (although
> qemu-nbd doesn't need to refer to it).
I tend to feel that this needs to be squashed into the previous
patch. The previous patch effectively creates unbounded memory
usage in the NBD server. ie consider a client that connects and
immediately disconnects, not sending any data, in a tight loop.
It will "leak" NBDConn & QIOChanelSocket pointers for each
iteration of the loop, only to be cleaned up when the NBD Server
is shutdown.
Especially given that we tagged the previous commit with a CVE
and not this commit, people could be misled into backporting
only the former commit leaving them open to the leak.
>
> Signed-off-by: Eric Blake <ebl...@redhat.com>
> ---
> include/block/nbd.h | 4 +++-
> blockdev-nbd.c | 27 ++++++++++++++++-----------
> nbd/server.c | 15 ++++++++++++---
> qemu-nbd.c | 2 +-
> 4 files changed, 32 insertions(+), 16 deletions(-)
>
> diff --git a/include/block/nbd.h b/include/block/nbd.h
> index 4e7bd6342f9..7dce9b9c35b 100644
> --- a/include/block/nbd.h
> +++ b/include/block/nbd.h
> @@ -405,7 +405,9 @@ NBDExport *nbd_export_find(const char *name);
> void nbd_client_new(QIOChannelSocket *sioc,
> 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/blockdev-nbd.c b/blockdev-nbd.c
> index b8f00f402c6..660f89d881e 100644
> --- a/blockdev-nbd.c
> +++ b/blockdev-nbd.c
> @@ -23,7 +23,7 @@
>
> typedef struct NBDConn {
> QIOChannelSocket *cioc;
> - QSLIST_ENTRY(NBDConn) next;
> + QLIST_ENTRY(NBDConn) next;
> } NBDConn;
>
> typedef struct NBDServerData {
> @@ -32,10 +32,11 @@ typedef struct NBDServerData {
> char *tlsauthz;
> uint32_t max_connections;
> uint32_t connections;
> - QSLIST_HEAD(, NBDConn) conns;
> + QLIST_HEAD(, NBDConn) conns;
> } NBDServerData;
>
> static NBDServerData *nbd_server;
> +static uint32_t nbd_cookie; /* Generation count of nbd_server */
> static int qemu_nbd_connections = -1; /* Non-negative if this is qemu-nbd */
>
> static void nbd_update_server_watch(NBDServerData *s);
> @@ -57,10 +58,16 @@ int nbd_server_max_connections(void)
>
> static void nbd_blockdev_client_closed(NBDClient *client, bool ignored)
> {
> + NBDConn *conn = nbd_client_owner(client);
> +
> assert(qemu_in_main_thread() && nbd_server);
>
> + object_unref(OBJECT(conn->cioc));
> + QLIST_REMOVE(conn, next);
> + g_free(conn);
> +
> nbd_client_put(client);
> - assert(nbd_server->connections > 0);
> + assert(nbd_server && nbd_server->connections > 0);
> nbd_server->connections--;
> nbd_update_server_watch(nbd_server);
> }
> @@ -74,12 +81,12 @@ static void nbd_accept(QIONetListener *listener,
> QIOChannelSocket *cioc,
> nbd_server->connections++;
> object_ref(OBJECT(cioc));
> conn->cioc = cioc;
> - QSLIST_INSERT_HEAD(&nbd_server->conns, conn, next);
> + QLIST_INSERT_HEAD(&nbd_server->conns, conn, next);
> nbd_update_server_watch(nbd_server);
>
> qio_channel_set_name(QIO_CHANNEL(cioc), "nbd-server");
> nbd_client_new(cioc, nbd_server->tlscreds, nbd_server->tlsauthz,
> - nbd_blockdev_client_closed);
> + nbd_blockdev_client_closed, conn);
> }
>
> static void nbd_update_server_watch(NBDServerData *s)
> @@ -93,6 +100,8 @@ static void nbd_update_server_watch(NBDServerData *s)
>
> static void nbd_server_free(NBDServerData *server)
> {
> + NBDConn *conn, *tmp;
> +
> if (!server) {
> return;
> }
> @@ -103,14 +112,9 @@ static void nbd_server_free(NBDServerData *server)
> */
> qio_net_listener_disconnect(server->listener);
> object_unref(OBJECT(server->listener));
> - while (!QSLIST_EMPTY(&server->conns)) {
> - NBDConn *conn = QSLIST_FIRST(&server->conns);
> -
> + QLIST_FOREACH_SAFE(conn, &server->conns, next, tmp) {
> qio_channel_shutdown(QIO_CHANNEL(conn->cioc),
> QIO_CHANNEL_SHUTDOWN_BOTH,
> NULL);
> - object_unref(OBJECT(conn->cioc));
> - QSLIST_REMOVE_HEAD(&server->conns, next);
> - g_free(conn);
> }
>
> AIO_WAIT_WHILE_UNLOCKED(NULL, server->connections > 0);
> @@ -119,6 +123,7 @@ static void nbd_server_free(NBDServerData *server)
> object_unref(OBJECT(server->tlscreds));
> }
> g_free(server->tlsauthz);
> + nbd_cookie++;
>
> g_free(server);
> }
> diff --git a/nbd/server.c b/nbd/server.c
> index 892797bb111..90f48b42a47 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -124,6 +124,7 @@ struct NBDMetaContexts {
> struct NBDClient {
> int refcount; /* atomic */
> void (*close_fn)(NBDClient *client, bool negotiated);
> + void *owner;
>
> QemuMutex lock;
>
> @@ -3205,14 +3206,15 @@ 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 and an indication of whether the client completed negotiation.
> */
> void nbd_client_new(QIOChannelSocket *sioc,
> QCryptoTLSCreds *tlscreds,
> const char *tlsauthz,
> - void (*close_fn)(NBDClient *, bool))
> + void (*close_fn)(NBDClient *, bool),
> + void *owner)
> {
> NBDClient *client;
> Coroutine *co;
> @@ -3231,7 +3233,14 @@ void nbd_client_new(QIOChannelSocket *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 d7b3ccab21c..da6e36a2a34 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -390,7 +390,7 @@ static void nbd_accept(QIONetListener *listener,
> QIOChannelSocket *cioc,
>
> nb_fds++;
> nbd_update_server_watch();
> - nbd_client_new(cioc, tlscreds, tlsauthz, nbd_client_closed);
> + nbd_client_new(cioc, tlscreds, tlsauthz, nbd_client_closed, NULL);
> }
>
> static void nbd_update_server_watch(void)
> --
> 2.45.2
>
With regards,
Daniel
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