json: fix error propagation when parsing binop lhs/rhs

Malformed input returns NULL when decoding left/right side of binop.
This causes a NULL dereference in expr_evaluate_binop; left/right must
point to a valid expression.

Fix this in the parser, else would have to sprinkle NULL checks all over
the evaluation code.

After fix, loading the bogon yields:
internal:0:0-0: Error: Malformed object (too many properties): '{}'.
internal:0:0-0: Error: could not decode binop rhs, '<<'.
internal:0:0-0: Error: Invalid mangle statement value
internal:0:0-0: Error: Parsing expr array at index 1 failed.
internal:0:0-0: Error: Parsing command array at index 3 failed.

Fixes: 0ac39384fd9e ("json: Accept more than two operands in binary expressions")
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 76 insertions, 0 deletions

diff --git a/tests/shell/testcases/bogons/nft-j-f/binop_rhs_decode_error_crash b/tests/shell/testcases/bogons/nft-j-f/binop_rhs_decode_error_crash
new file mode 100644
index 00000000..8b5b7290
--- /dev/null
+++ b/tests/shell/testcases/bogons/nft-j-f/binop_rhs_decode_error_crash
@@ -0,0 +1,76 @@
+{
+  "nftables": [
+    {
+      "metainfo": {
+        "version": "VERSION",
+        "release_name": "RELEASE_NAME",
+        "json_schema_version": 1
+      }
+    },
+    {
+      "table": {
+        "family": "ip",
+        "name": "t",
+        "handle": 0
+      }
+    },
+    {
+      "chain": {
+        "family": "ip",
+        "table": "t",
+        "name": "c",
+        "handle": 0,
+        "type": "filter",
+        "hook": "output",
+        "prio": 0,
+        "policy": "accept"
+      }
+    },
+    {
+      "rule": {
+        "family": "ip",
+        "table": "t",
+        "chain": "c",
+        "handle": 0,
+        "expr": [
+          {
+            "match": {
+              "op": "==",
+              "left": {
+                "meta": {
+                  "key": "oif"
+                }
+              },
+              "right": "lo"
+            }
+          },
+          {
+            "mangle": {
+              "key": {
+                "ct": {
+                  "key": "mark"
+                }
+              },
+              "value": {
+                "<<": [
+                  {
+                    "|": [
+                      {
+                        "meta": {
+                          "key": "mark"
+                        }
+                      },
+                      16
+                    ]
+                  },
+                  {  },
+                  8
+                ]
+              }
+            }
+          }
+        ]
+      }
+    }
+  ]
+}