[Qemu-devel] [PATCH 3/3] nbd: Reject unknown request flags

[Eric Blake <eblake@redhat.com>]

The NBD protocol says that clients should not send a command flag
that has not been negotiated (whether by the client requesting an
option during a handshake, or because we advertise support for the
flag in response to NBD_OPT_EXPORT_NAME), and that servers should
reject invalid flags with EINVAL.  We were silently ignoring the
flags instead.  The client can't rely on our behavior, since it is
their fault for passing the bad flag in the first place, but it's
better to be robust up front than to possibly behave differently
than the client was expecting with the attempted flag.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 nbd/server.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/nbd/server.c b/nbd/server.c
index a590773..31bd9c5 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -974,6 +974,10 @@ static ssize_t nbd_co_receive_request(NBDRequest *req, struct nbd_request *reque
         goto out;
     }

+    if (request->flags & ~NBD_CMD_FLAG_FUA) {
+        LOG("unsupported flags (got 0x%x)", request->flags);
+        return -EINVAL;
+    }
     if ((request->from + request->len) < request->from) {
         LOG("integer overflow detected! "
             "you're probably being attacked");
-- 
2.5.5