Fix segmentation fault in Ingester.LabelValues response marshaling (#…

…8003)

* Copy label values out of mmapped region before returning from RPC handler.

* comment touchup

* Add changelog message.

* Update CHANGELOG.md

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

---------

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

CHANGELOG.md

@@ -44,6 +44,7 @@
 * [BUGFIX] Distributor: fix down scaling of native histograms in the distributor when timeseries unmarshal cache is in use. #7947
 * [BUGFIX] Distributor: fix cardinality API to return more accurate number of in-memory series when number of zones is larger than replication factor. #7984
 * [BUGFIX] All: fix config validation for non-ingester modules, when ingester's ring is configured with spread-minimizing token generation strategy. #7990
+* [BUGFIX] Ingester: copy LabelValues strings out of mapped memory to avoid a segmentation fault if the region becomes unmapped before the result is marshaled. #8003
 
 ### Mixin
 

pkg/ingester/ingester.go

@@ -1652,6 +1652,13 @@ func (i *Ingester) LabelValues(ctx context.Context, req *client.LabelValuesReque
 		return nil, err
 	}
 
+	// The label value strings are sometimes pointing to memory mapped file
+	// regions that may become unmapped anytime after Querier.Close is called.
+	// So we copy those strings.
+	for i, s := range vals {
+		vals[i] = strings.Clone(s)
+	}
+
 	return &client.LabelValuesResponse{
 		LabelValues: vals,
 	}, nil