Limit VADD REDUCE dim to not exceed original dim

* Limit VADD REDUCE dim to not exceed original dim

Enforce VADD key [REDUCE dim]  to reject dim that is bigger than the HNSW original dim, as dimension reduction makes no sense for reduce_dim > original_dim.
This also avoids OOM and possible heap overflow on later allocations using reduce_dim.

This should be backported to Redis version 8.0, 8.2 and 8.4.

modules/vector-sets/tests/dimension_validation.py

@@ -65,3 +65,33 @@ class DimensionValidation(TestCase):
             assert False, "VSIM with wrong dimension should fail"
         except redis.exceptions.ResponseError as e:
             assert "Input dimension mismatch for projection" in str(e), f"Expected dimension mismatch error in VSIM, got: {e}"
+
+class ReduceDimConstraintValidation(TestCase):
+    def getname(self):
+        return "[regression] VADD enforces reduce_dim <= dim"
+
+    def estimated_runtime(self):
+        return 0.1
+
+    def test(self):
+        import struct
+
+        dim = 16
+        reduce_dim = dim + 1  # Intentionally larger than dim
+
+        # Build a simple FP32 vector of the given dimension.
+        vec = [0.0] * dim
+        vec_bytes = struct.pack(f'{dim}f', *vec)
+
+        try:
+            self.redis.execute_command(
+                'VADD', self.test_key,
+                'REDUCE', reduce_dim,
+                'FP32', vec_bytes,
+                f'{self.test_key}:item:reducemismatch')
+            assert False, "VADD with reduce_dim > dim should fail"
+        except redis.exceptions.ResponseError as e:
+            # Same generic validation error path as other vector spec problems.
+            assert "invalid vector specification" in str(e), (
+                f"Expected invalid vector error, got: {e}")
+

modules/vector-sets/vset.c

@@ -445,6 +445,12 @@ float *parseVector(RedisModuleString **argv, int argc, int start_idx,
         return NULL;  // Unknown format.
     }
 
+    // reduce_dim must be <= dim
+    if (reduce_dim && *reduce_dim && *reduce_dim > *dim) {
+        if (vec) RedisModule_Free(vec);
+        return NULL;
+    }
+
     if (consumed_args) *consumed_args = consumed;
     return vec;
 }