Re: [Qemu-devel] [PATCH v6 06/12] nbd/server: Refactor zero-length option check

[Eric Blake]

On 10/30/2017 06:22 PM, Vladimir Sementsov-Ogievskiy wrote:
> 27.10.2017 13:40, Eric Blake wrote:
>> Consolidate the response for a non-zero-length option payload
>> into a new function, nbd_reject_length().  This check will
>> also be used when introducing support for structured replies.
>>
>> Note that STARTTLS response differs based on time: if the connection
>> is still unencrypted, we set fatal to true (a client that can't
>> request TLS correctly may still think that we are ready to start
>> the TLS handshake, so we must disconnect); while if the connection
>> is already encrypted, the client is sending a bogus request but
>> is no longer at risk of being confused by continuing the connection.
>>

>>               switch (option) {
>>               case NBD_OPT_STARTTLS:
>> -                tioc = nbd_negotiate_handle_starttls(client, length,
>> errp);
>> +                if (length) {
>> +                    /* Unconditionally drop the connection if the client
>> +                     * can't start a TLS negotiation correctly */
>> +                    nbd_reject_length(client, length, option, true,
>> errp);
>> +                    return -EINVAL;
> 
> why not to return nbd_reject_length's result? this EINVAL may not
> correspond to errp (about EIO for example)..

Somewhat true, if nbd_reject_length() fails. But nbd_reject_length() may
also return 0 without setting errp, in which case, maybe this code
should set errp rather than just blindly returning -EINVAL.

> 
> with or without this fixed:
> 
> Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> 

Okay, I'll squash this in, and include it in my pull request to be sent
shortly.

diff --git i/nbd/server.c w/nbd/server.c
index a9480e42cd..91f81a0f19 100644
--- i/nbd/server.c
+++ w/nbd/server.c
@@ -684,8 +684,13 @@ static int nbd_negotiate_options(NBDClient *client,
uint16_t myflags,
                 if (length) {
                     /* Unconditionally drop the connection if the client
                      * can't start a TLS negotiation correctly */
-                    nbd_reject_length(client, length, option, true, errp);
-                    return -EINVAL;
+                    ret = nbd_reject_length(client, length, option,
true, errp);
+                    if (!ret) {
+                        error_setg(errp, "option '%s' should have zero
length",
+                                   nbd_opt_lookup(option));
+                        ret = -EINVAL;
+                    }
+                    return ret;
                 }
                 tioc = nbd_negotiate_handle_starttls(client, errp);
                 if (!tioc) {


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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