On Sat, Dec 15, 2018 at 07:53:14AM -0600, Eric Blake wrote:
Always allocate space for the reply returned by the server and
hoist the trace earlier, as it is more interesting to trace the
server's reply (even if it is unexpected) than parroting our
request only on success. After all, skipping the allocation
for a wrong size was merely a micro-optimization that only
benefitted a broken server, rather than the common case of a
compliant server that meets our expectations.
Then turn the reply handling into a loop (even though we still
never iterate more than once), to make this code easier to use
when later patches do support multiple server replies. This
changes the error message for a server with two replies (a
corner case we are unlikely to hit in practice) from:
Unexpected reply type 4 (meta context), expected 0 (ack)
to:
Server replied with more than one context
Signed-off-by: Eric Blake <address@hidden>
---
v2: split patch into easier-to-review pieces [Rich, Vladimir]
---
nbd/client.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/nbd/client.c b/nbd/client.c
index bcccd5f555e..b6a85fc3ef8 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -684,10 +684,11 @@ static int nbd_negotiate_simple_meta_context(QIOChannel
*ioc,
return ret;
}
- if (reply.type == NBD_REP_META_CONTEXT) {
+ while (reply.type == NBD_REP_META_CONTEXT) {
I'm not sure I understand why this change is safe.
As far as I can see reply.type is only updated in the loop by
nbd_receive_option_reply, and that reads from the server, and so the
server might keep sending NBD_REP_META_CONTEXT packets (instead of the
expected NBD_REP_ACK), so it could now loop forever against a
malicious server? (This is not taking into account any later patches)