From 59d76faa1bb4b3cf79fb7c8ae1265cebba8a7f7c Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Thu, 3 May 2018 17:26:26 -0500 Subject: [PATCH] nbd/client: Relax handling of large NBD_CMD_BLOCK_STATUS reply The NBD spec is proposing a relaxation of NBD_CMD_BLOCK_STATUS where a server may have the final extent per context give a length beyond the original request, if it can easily prove that subsequent bytes have the same status, on the grounds that a client can take advantage of this information for fewer block status requests. Since qemu 2.12 as a client always sends NBD_CMD_FLAG_REQ_ONE, and rejects a server that sends extra length, the upstream NBD spec will probably limit this behavior to clients that don't request REQ_ONE semantics; but it doesn't hurt to relax qemu to always be permissive of this server behavior, even if it continues to use REQ_ONE. CC: qemu-stable@nongnu.org Signed-off-by: Eric Blake Message-Id: <20180503222626.1303410-1-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy (cherry picked from commit acfd8f7a5f92e703d2d046cbe3d510008a697194) Signed-off-by: Bruce Rogers --- block/nbd-client.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/block/nbd-client.c b/block/nbd-client.c index e7caf49fbb..8d69eaaa32 100644 --- a/block/nbd-client.c +++ b/block/nbd-client.c @@ -259,14 +259,18 @@ static int nbd_parse_blockstatus_payload(NBDClientSession *client, if (extent->length == 0 || (client->info.min_block && !QEMU_IS_ALIGNED(extent->length, - client->info.min_block)) || - extent->length > orig_length) - { + client->info.min_block))) { error_setg(errp, "Protocol error: server sent status chunk with " "invalid length"); return -EINVAL; } + /* The server is allowed to send us extra information on the final + * extent; just clamp it to the length we requested. */ + if (extent->length > orig_length) { + extent->length = orig_length; + } + return 0; }