evaluate: don't crash if object map does not refer to a value

Before:
BUG: Value export of 512 bytes would overflownft: src/netlink.c:474: netlink_gen_prefix: Assertion `0' failed.

After:
66: Error: Object mapping data should be a value, not prefix
synproxy name ip saddr map { 192.168.1.0/24 : "v*" }

Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/tests/shell/testcases/bogons/nft-f/objmap_to_prefix_assert b/tests/shell/testcases/bogons/nft-f/objmap_to_prefix_assert
new file mode 100644
index 00000000..d880a377
--- /dev/null
+++ b/tests/shell/testcases/bogons/nft-f/objmap_to_prefix_assert
@@ -0,0 +1,6 @@
+table t {
+        chain y {
+                type filter hook input priority filter; policy accept;
+                synproxy name ip saddr map { 192.168.1.0/24 : "x*" }
+        }
+}