From d21a2d3451d7f1defea5104ce28938f228fab0d4 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Thu, 17 Jan 2019 13:36:54 -0600 Subject: nbd/client: Add 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 adds the low-level client code for grabbing the list of exports. It benefits from the recent refactoring patches, in order to share as much code as possible when it comes to doing validation of server replies. The resulting information is stored in an array of NBDExportInfo which has been expanded to any description string, along with a convenience function for freeing the list. Note: a malicious server could exhaust memory of a client by feeding an unending loop of exports; perhaps we should place a limit on how many we are willing to receive. But note that a server could reasonably be serving an export for every file in a large directory, where an arbitrary limit in the client means we can't list anything from such a server; the same happens if we just run until the client fails to malloc() and thus dies by an abort(), where the limit is no longer arbitrary but determined by available memory. Since the client is already planning on being short-lived, it's hard to call this a denial of service attack that would starve off other uses, so it does not appear to be a security issue. Signed-off-by: Eric Blake Reviewed-by: Richard W.M. Jones Message-Id: <20190117193658.16413-18-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy --- nbd/client.c | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 130 insertions(+), 2 deletions(-) (limited to 'nbd') diff --git a/nbd/client.c b/nbd/client.c index fa1657a..8a32169 100644 --- a/nbd/client.c +++ b/nbd/client.c @@ -836,7 +836,9 @@ static int nbd_start_negotiate(QIOChannel *ioc, QCryptoTLSCreds *tlscreds, trace_nbd_start_negotiate(tlscreds, hostname ? hostname : ""); - *zeroes = true; + if (zeroes) { + *zeroes = true; + } if (outioc) { *outioc = NULL; } @@ -880,7 +882,9 @@ static int nbd_start_negotiate(QIOChannel *ioc, QCryptoTLSCreds *tlscreds, clientflags |= NBD_FLAG_C_FIXED_NEWSTYLE; } if (globalflags & NBD_FLAG_NO_ZEROES) { - *zeroes = false; + if (zeroes) { + *zeroes = false; + } clientflags |= NBD_FLAG_C_NO_ZEROES; } /* client requested flags */ @@ -1059,6 +1063,130 @@ int nbd_receive_negotiate(QIOChannel *ioc, QCryptoTLSCreds *tlscreds, return 0; } +/* Clean up result of nbd_receive_export_list */ +void nbd_free_export_list(NBDExportInfo *info, int count) +{ + int i; + + if (!info) { + return; + } + + for (i = 0; i < count; i++) { + g_free(info[i].name); + g_free(info[i].description); + } + g_free(info); +} + +/* + * nbd_receive_export_list: + * Query details about a server's exports, then disconnect without + * going into transmission phase. Return a count of the exports listed + * in @info by the server, or -1 on error. Caller must free @info using + * nbd_free_export_list(). + */ +int nbd_receive_export_list(QIOChannel *ioc, QCryptoTLSCreds *tlscreds, + const char *hostname, NBDExportInfo **info, + Error **errp) +{ + int result; + int count = 0; + int i; + int rc; + int ret = -1; + NBDExportInfo *array = NULL; + QIOChannel *sioc = NULL; + + *info = NULL; + result = nbd_start_negotiate(ioc, tlscreds, hostname, &sioc, true, NULL, + errp); + if (tlscreds && sioc) { + ioc = sioc; + } + + switch (result) { + case 2: + case 3: + /* newstyle - use NBD_OPT_LIST to populate array, then try + * NBD_OPT_INFO on each array member. If structured replies + * are enabled, also try NBD_OPT_LIST_META_CONTEXT. */ + if (nbd_send_option_request(ioc, NBD_OPT_LIST, 0, NULL, errp) < 0) { + goto out; + } + while (1) { + char *name; + char *desc; + + rc = nbd_receive_list(ioc, &name, &desc, errp); + if (rc < 0) { + goto out; + } else if (rc == 0) { + break; + } + array = g_renew(NBDExportInfo, array, ++count); + memset(&array[count - 1], 0, sizeof(*array)); + array[count - 1].name = name; + array[count - 1].description = desc; + array[count - 1].structured_reply = result == 3; + } + + for (i = 0; i < count; i++) { + array[i].request_sizes = true; + rc = nbd_opt_info_or_go(ioc, NBD_OPT_INFO, &array[i], errp); + if (rc < 0) { + goto out; + } else if (rc == 0) { + /* + * Pointless to try rest of loop. If OPT_INFO doesn't work, + * it's unlikely that meta contexts work either + */ + break; + } + + /* TODO: Grab meta contexts */ + } + + /* Send NBD_OPT_ABORT as a courtesy before hanging up */ + nbd_send_opt_abort(ioc); + break; + case 1: /* newstyle, but limited to EXPORT_NAME */ + error_setg(errp, "Server does not support export lists"); + /* We can't even send NBD_OPT_ABORT, so merely hang up */ + goto out; + case 0: /* oldstyle, parse length and flags */ + array = g_new0(NBDExportInfo, 1); + array->name = g_strdup(""); + count = 1; + + if (nbd_negotiate_finish_oldstyle(ioc, array, errp) < 0) { + goto out; + } + + /* Send NBD_CMD_DISC as a courtesy to the server, but ignore all + * errors now that we have the information we wanted. */ + if (nbd_drop(ioc, 124, NULL) == 0) { + NBDRequest request = { .type = NBD_CMD_DISC }; + + nbd_send_request(ioc, &request); + } + break; + default: + goto out; + } + + *info = array; + array = NULL; + ret = count; + + out: + qio_channel_shutdown(ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL); + qio_channel_close(ioc, NULL); + object_unref(OBJECT(sioc)); + nbd_free_export_list(array, count); + return ret; +} + #ifdef __linux__ int nbd_init(int fd, QIOChannelSocket *sioc, NBDExportInfo *info, Error **errp) -- cgit v1.1