nbd/server: Prefer heap over stack for parsing client names

As long as we limit NBD names to 256 bytes (the bare minimum permitted
by the standard), stack-allocation works for parsing a name received
from the client.  But as mentioned in a comment, we eventually want to
permit up to the 4k maximum of the NBD standard, which is too large
for stack allocation; so switch everything in the server to use heap
allocation.  For now, there is no change in actually supported name
length.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20191114024635.11363-2-eblake@redhat.com>
[eblake: fix uninit variable compile failure]
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/include/block/nbd.h b/include/block/nbd.h
index 316fd705a9..c306423dc8 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -226,11 +226,11 @@ enum {
 /* Maximum size of a single READ/WRITE data buffer */
 #define NBD_MAX_BUFFER_SIZE (32 * 1024 * 1024)
 
-/* Maximum size of an export name. The NBD spec requires 256 and
- * suggests that servers support up to 4096, but we stick to only the
- * required size so that we can stack-allocate the names, and because
- * going larger would require an audit of more code to make sure we
- * aren't overflowing some other buffer. */
+/*
+ * Maximum size of an export name. The NBD spec requires a minimum of
+ * 256 and recommends that servers support up to 4096; all users use
+ * malloc so we can bump this constant without worry.
+ */
 #define NBD_MAX_NAME_SIZE 256
 
 /* Two types of reply structures */