[Qemu-devel] [PATCH 2/2] nbd: Fix server reply to NBD_OPT_EXPORT_NAME of older clients

[Eric Blake]

A typo in commit 23e099c set the size of buf[] used in response
to NBD_OPT_EXPORT_NAME according to the length needed for old-style
negotiation (4 bytes of flag information) instead of the intended
2 bytes used in new style.  If the client doesn't enable
NBD_FLAG_C_NO_ZEROES, then the server sends two bytes too many,
and is then out of sync in response to the client's next command
(the bug is masked when modern qemu is the client, since we enable
the no zeroes flag).

Signed-off-by: Eric Blake <address@hidden>
---
 nbd/server.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index 49ed574..bcb241c 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -283,7 +283,7 @@ static int nbd_negotiate_handle_export_name(NBDClient 
*client, uint32_t length,
                                             Error **errp)
 {
     char name[NBD_MAX_NAME_SIZE + 1];
-    char buf[8 + 4 + 124] = "";
+    char buf[8 + 2 + 124] = "";
     size_t len;
     int ret;

@@ -800,7 +800,7 @@ static int nbd_negotiate_options(NBDClient *client, 
uint16_t myflags,
  */
 static coroutine_fn int nbd_negotiate(NBDClient *client, Error **errp)
 {
-    char buf[8 + 8 + 8 + 128];
+    char buf[8 + 8 + 8 + 2 + 2 + 124];
     int ret;
     const uint16_t myflags = (NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM |
                               NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA |
-- 
2.9.4