Fix null pointer access when copying into a slice with larger cap but smaller len

.chloggen/fix-copy.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: pdata
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix null pointer access when copying into a slice with larger cap but smaller len.
+
+# One or more tracking issues or pull requests related to the change
+issues: [13523]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

internal/cmd/pdatagen/internal/templates/slice.go.tmpl

@@ -199,19 +199,41 @@ func (ms {{ .structName }}) unmarshalJSONIter(iter *json.Iterator) {
 }
 
 func copyOrig{{ .structName }}(dest, src []{{ .originElementType }}) []{{ .originElementType }} {
+	var newDest []{{ .originElementType }}
 	if cap(dest) < len(src) {
-		dest = make([]{{ .originElementType }}, len(src))
 		{{- if eq .type "sliceOfPtrs" }}
-		data := make([]{{ .originName }}, len(src))
-		for i := range src {
-			dest[i] = &data[i]
+		newDest = make([]{{ .originElementType }}, len(src))
+		// Copy old pointers to re-use.
+		copy(newDest, dest)
+		// Add new pointers for missing elements from len(dest) to len(srt).
+		for i := len(dest); i < len(src); i++ {
+			newDest[i] = &{{ .originName }}{}
+		}
+		{{- else }}
+		newDest = make([]{{ .originElementType }}, len(src))
+		{{- end }}
+	} else {
+		newDest = dest[:len(src)]
+		// Cleanup the rest of the elements so GC can free the memory.
+		// This can happen when len(src) < len(dest) < cap(dest).
+		{{- if eq .type "sliceOfPtrs" }}
+		for i := len(src); i < len(dest); i++ {
+			dest[i] = nil
+		}
+		// Add new pointers for missing elements.
+		// This can happen when len(dest) < len(src) < cap(dest).
+		for i := len(dest); i < len(src); i++ {
+			newDest[i] = &{{ .originName }}{}
+		}
+		{{- else }}
+		for i := len(src); i < len(dest); i++ {
+			dest[i] = {{ .emptyOriginElement }}
 		}
 		{{- end }}
 	}
-	dest = dest[:len(src)]
 	for i := range src {
-		copyOrig{{ .elementName }}({{ .originElementPtr }}dest[i], {{ .originElementPtr }}src[i])
+		copyOrig{{ .elementName }}({{ .originElementPtr }}newDest[i], {{ .originElementPtr }}src[i])
 	}
-	return dest
+	return newDest
 }
 {{- end }}

internal/cmd/pdatagen/internal/templates/slice_internal.go.tmpl

@@ -32,20 +32,42 @@ func New{{ .structName }}(orig *[]{{ .originElementType }}, state *State) {{ .st
 }
 
 func CopyOrig{{ .structName }}(dest, src []{{ .originElementType }}) []{{ .originElementType }} {
+	var newDest []{{ .originElementType }}
 	if cap(dest) < len(src) {
-		dest = make([]{{ .originElementType }}, len(src))
 		{{- if eq .type "sliceOfPtrs" }}
-		data := make([]{{ .originName }}, len(src))
-		for i := range src {
-			dest[i] = &data[i]
+		newDest = make([]{{ .originElementType }}, len(src))
+		// Copy old pointers to re-use.
+		copy(newDest, dest)
+		// Add new pointers for missing elements from len(dest) to len(srt).
+		for i := len(dest); i < len(src); i++ {
+			newDest[i] = &{{ .originName }}{}
+		}
+		{{- else }}
+		newDest = make([]{{ .originElementType }}, len(src))
+		{{- end }}
+	} else {
+		newDest = dest[:len(src)]
+		// Cleanup the rest of the elements so GC can free the memory.
+		// This can happen when len(src) < len(dest) < cap(dest).
+		{{- if eq .type "sliceOfPtrs" }}
+		for i := len(src); i < len(dest); i++ {
+		dest[i] = nil
+		}
+		// Add new pointers for missing elements.
+		// This can happen when len(dest) < len(src) < cap(dest).
+		for i := len(dest); i < len(src); i++ {
+		newDest[i] = &{{ .originName }}{}
+		}
+		{{- else }}
+		for i := len(src); i < len(dest); i++ {
+		dest[i] = {{ .emptyOriginElement }}
 		}
 		{{- end }}
 	}
-	dest = dest[:len(src)]
 	for i := range src {
-		CopyOrig{{ .elementName }}({{ .originElementPtr }}dest[i], {{ .originElementPtr }}src[i])
+		CopyOrig{{ .elementName }}({{ .originElementPtr }}newDest[i], {{ .originElementPtr }}src[i])
 	}
-	return dest
+	return newDest
 }
 
 func GenerateTest{{ .structName }}() {{ .structName }} {

internal/cmd/pdatagen/internal/templates/slice_test.go.tmpl

@@ -53,16 +53,25 @@ func Test{{ .structName }}ReadOnly(t *testing.T) {
 
 func Test{{ .structName }}_CopyTo(t *testing.T) {
 	dest := New{{ .structName }}()
-	// Test CopyTo to empty
+	// Test CopyTo empty
 	New{{ .structName }}().CopyTo(dest)
 	assert.Equal(t, New{{ .structName }}(), dest)
 
-	// Test CopyTo larger slice
-	generateTest{{ .structName }}().CopyTo(dest)
+	// Test CopyTo larger slice and EnsureCapacity
+	src := generateTest{{ .structName }}()
+	src.CopyTo(dest)
 	assert.Equal(t, generateTest{{ .structName }}(), dest)
 
 	// Test CopyTo same size slice
-	generateTest{{ .structName }}().CopyTo(dest)
+	src.CopyTo(dest)
+	assert.Equal(t, generateTest{{ .structName }}(), dest)
+}
+
+func Test{{ .structName }}_CopyToAndEnsureCapacity(t *testing.T) {
+	dest := New{{ .structName }}()
+	src := generateTest{{ .structName }}()
+	dest.EnsureCapacity(src.Len())
+	src.CopyTo(dest)
 	assert.Equal(t, generateTest{{ .structName }}(), dest)
 }