From 0b576b6bfb56291bb13db0a54d99adf2f3706030 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Thu, 17 Jan 2019 13:36:55 -0600 Subject: [PATCH] nbd/client: Add meta contexts to nbd_receive_export_list() We want to be able to detect whether a given qemu NBD server is exposing the right export(s) and dirty bitmaps, at least for regression testing. We could use 'nbd-client -l' from the upstream NBD project to list exports, but it's annoying to rely on out-of-tree binaries; furthermore, nbd-client doesn't necessarily know about all of the qemu NBD extensions. Thus, we plan on adding a new mode to qemu-nbd that merely sniffs all possible information from the server during handshake phase, then disconnects and dumps the information. This patch continues the work of the previous patch, by adding the ability to track the list of available meta contexts into NBDExportInfo. It benefits from the recent refactoring patches with a new nbd_list_meta_contexts() that reuses much of the same framework as setting a meta context. Note: a malicious server could exhaust memory of a client by feeding an unending loop of contexts; perhaps we could place a limit on how many we are willing to receive. But this is no different from our earlier analysis on a server sending an unending list of exports, and the death of a client due to memory exhaustion when the client was going to exit soon anyways is not really a denial of service attack. Signed-off-by: Eric Blake Reviewed-by: Richard W.M. Jones Reviewed-by: Vladimir Sementsov-Ogievskiy Message-Id: <20190117193658.16413-19-eblake@redhat.com> --- include/block/nbd.h | 2 ++ nbd/client.c | 41 +++++++++++++++++++++++++++++++++++++++-- 2 files changed, 41 insertions(+), 2 deletions(-) diff --git a/include/block/nbd.h b/include/block/nbd.h index 19332b4671..4faf394e34 100644 --- a/include/block/nbd.h +++ b/include/block/nbd.h @@ -284,6 +284,8 @@ struct NBDExportInfo { /* Set by server results during nbd_receive_export_list() */ char *description; + int n_contexts; + char **contexts; }; typedef struct NBDExportInfo NBDExportInfo; diff --git a/nbd/client.c b/nbd/client.c index 8a32169970..798b82f205 100644 --- a/nbd/client.c +++ b/nbd/client.c @@ -817,6 +817,36 @@ static int nbd_negotiate_simple_meta_context(QIOChannel *ioc, return received; } +/* + * nbd_list_meta_contexts: + * Request the server to list all meta contexts for export @info->name. + * return 0 if list is complete (even if empty), + * -1 with errp set for any error + */ +static int nbd_list_meta_contexts(QIOChannel *ioc, + NBDExportInfo *info, + Error **errp) +{ + int ret; + + if (nbd_send_meta_query(ioc, NBD_OPT_LIST_META_CONTEXT, + info->name, NULL, errp) < 0) { + return -1; + } + + while (1) { + char *context; + + ret = nbd_receive_one_meta_context(ioc, NBD_OPT_LIST_META_CONTEXT, + &context, NULL, errp); + if (ret <= 0) { + return ret; + } + info->contexts = g_renew(char *, info->contexts, ++info->n_contexts); + info->contexts[info->n_contexts - 1] = context; + } +} + /* * nbd_start_negotiate: * Start the handshake to the server. After a positive return, the server @@ -1066,7 +1096,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, QCryptoTLSCreds *tlscreds, /* Clean up result of nbd_receive_export_list */ void nbd_free_export_list(NBDExportInfo *info, int count) { - int i; + int i, j; if (!info) { return; @@ -1075,6 +1105,10 @@ void nbd_free_export_list(NBDExportInfo *info, int count) for (i = 0; i < count; i++) { g_free(info[i].name); g_free(info[i].description); + for (j = 0; j < info[i].n_contexts; j++) { + g_free(info[i].contexts[j]); + } + g_free(info[i].contexts); } g_free(info); } @@ -1144,7 +1178,10 @@ int nbd_receive_export_list(QIOChannel *ioc, QCryptoTLSCreds *tlscreds, break; } - /* TODO: Grab meta contexts */ + if (result == 3 && + nbd_list_meta_contexts(ioc, &array[i], errp) < 0) { + goto out; + } } /* Send NBD_OPT_ABORT as a courtesy before hanging up */