Up to nbdkit 1.22, we never advertised large export lists, so a client had no real reason to give more than 32 NBD_OPT_ commands before finally selecting an export or quitting, and we were justified in dropping indecisive chatty clients as being a waste of server resources. But now that we support .list_exports, it is reasonable for a client (such as 'qemu-nbd --list' or 'nbdinfo --list') to want to call NBD_OPT_INFO and several NBD_OPT_LIST_META_CONTEXT commands for every export returned in NBD_OPT_LIST. We still want to avoid clients that can tie us up in eternal handshaking, so let's reject a second call to NBD_OPT_LIST; but once the first call is made, the client now has a chance to get info on everything listed. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- server/protocol-handshake-newstyle.c | 49 ++++++++++++++++++++-------- 1 file changed, 35 insertions(+), 14 deletions(-) diff --git a/server/protocol-handshake-newstyle.c b/server/protocol-handshake-newstyle.c index 9c86639b..dedb7f9d 100644 --- a/server/protocol-handshake-newstyle.c +++ b/server/protocol-handshake-newstyle.c @@ -44,5 +44,8 @@ #include "nbd-protocol.h" #include "protostrings.h" -/* Maximum number of client options we allow before giving up. */ +/* Initial bound of client options we allow before giving up. + * However, a client that issues NBD_OPT_LIST is permitted to follow + * up with another round of options per export listed. + */ #define MAX_NR_OPTIONS 32 /* Receive newstyle options. */ @@ -78,12 +81,13 @@ send_newstyle_option_reply (uint32_t option, uint32_t reply) /* Reply to NBD_OPT_LIST with the plugin's list of export names. */ static int -send_newstyle_option_reply_exportnames (uint32_t option) +send_newstyle_option_reply_exportnames (uint32_t option, size_t *nr_options) { GET_CONN; struct nbd_fixed_new_option_reply fixed_new_option_reply; - size_t i; + size_t i, list_len; CLEANUP_EXPORTS_FREE struct nbdkit_exports *exps = NULL; + int r; exps = nbdkit_exports_new (); if (exps == NULL) @@ -91,7 +95,8 @@ send_newstyle_option_reply_exportnames (uint32_t option) if (backend_list_exports (top, read_only, exps) == -1) return send_newstyle_option_reply (option, NBD_REP_ERR_PLATFORM); - for (i = 0; i < nbdkit_exports_count (exps); i++) { + list_len = nbdkit_exports_count (exps); + for (i = 0; i < list_len; i++) { const struct nbdkit_export export = nbdkit_get_export (exps, i); size_t name_len = strlen (export.name); size_t desc_len = export.description ? strlen (export.description) : 0; @@ -127,7 +132,11 @@ send_newstyle_option_reply_exportnames (uint32_t option) } } - return send_newstyle_option_reply (option, NBD_REP_ACK); + r = send_newstyle_option_reply (option, NBD_REP_ACK); + /* Allow additional per-export NBD_OPT_INFO and friends. */ + if (r == 0) + *nr_options += MAX_NR_OPTIONS * list_len; + return r; } static int @@ -326,6 +335,7 @@ negotiate_handshake_newstyle_options (void) GET_CONN; struct nbd_new_option new_option; size_t nr_options; + bool list_seen = false; uint64_t version; uint32_t option; uint32_t optlen; @@ -334,7 +344,7 @@ negotiate_handshake_newstyle_options (void) uint64_t exportsize; struct backend *b; - for (nr_options = 0; nr_options < MAX_NR_OPTIONS; ++nr_options) { + for (nr_options = MAX_NR_OPTIONS; nr_options > 0; --nr_options) { CLEANUP_FREE char *data = NULL; if (conn_recv_full (&new_option, sizeof new_option, @@ -431,11 +441,22 @@ negotiate_handshake_newstyle_options (void) continue; } - /* Send back the exportname list. */ - debug ("newstyle negotiation: %s: advertising exports", - name_of_nbd_opt (option)); - if (send_newstyle_option_reply_exportnames (option) == -1) - return -1; + if (list_seen) { + debug ("newstyle negotiation: %s: export list already advertised", + name_of_nbd_opt (option)); + if (send_newstyle_option_reply (option, NBD_REP_ERR_INVALID) + == -1) + return -1; + continue; + } + else { + /* Send back the exportname list. */ + debug ("newstyle negotiation: %s: advertising exports", + name_of_nbd_opt (option)); + if (send_newstyle_option_reply_exportnames (option, &nr_options) == -1) + return -1; + list_seen = true; + } break; case NBD_OPT_STARTTLS: @@ -826,8 +847,8 @@ negotiate_handshake_newstyle_options (void) break; } - if (nr_options >= MAX_NR_OPTIONS) { - nbdkit_error ("client exceeded maximum number of options (%d)", - MAX_NR_OPTIONS); + if (nr_options == 0) { + nbdkit_error ("client spent too much time negotiating without selecting " + "an export"); return -1; } -- 2.28.0