go/parser: track depth in nested element lists

Prevents stack exhaustion with extremely deeply nested literal values,
i.e. field values in structs.

Fixes #69138
Fixes CVE-2024-34155

Change-Id: I2e8e33b44105cc169d7ed1ae83fb56df0c10f1ee
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/1520
Reviewed-by: Robert Griesemer <[email protected]>
Reviewed-by: Damien Neil <[email protected]>
Reviewed-by: Russ Cox <[email protected]>
Reviewed-on: https://go-review.googlesource.com/c/go/+/611238
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Roland Shoemaker <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>

Author: rolandshoemaker

src/go/parser/parser.go

@@ -1676,6 +1676,8 @@ func (p *parser) parseElementList() (list []ast.Expr) {
 }
 
 func (p *parser) parseLiteralValue(typ ast.Expr) ast.Expr {
+	defer decNestLev(incNestLev(p))
+
 	if p.trace {
 		defer un(trace(p, "LiteralValue"))
 	}

src/go/parser/parser_test.go

@@ -598,10 +598,11 @@ var parseDepthTests = []struct {
 	{name: "chan2", format: "package main; var x «<-chan »int"},
 	{name: "interface", format: "package main; var x «interface { M() «int» }»", scope: true, scopeMultiplier: 2}, // Scopes: InterfaceType, FuncType
 	{name: "map", format: "package main; var x «map[int]»int"},
-	{name: "slicelit", format: "package main; var x = «[]any{«»}»", parseMultiplier: 2},             // Parser nodes: UnaryExpr, CompositeLit
-	{name: "arraylit", format: "package main; var x = «[1]any{«nil»}»", parseMultiplier: 2},         // Parser nodes: UnaryExpr, CompositeLit
-	{name: "structlit", format: "package main; var x = «struct{x any}{«nil»}»", parseMultiplier: 2}, // Parser nodes: UnaryExpr, CompositeLit
-	{name: "maplit", format: "package main; var x = «map[int]any{1:«nil»}»", parseMultiplier: 2},    // Parser nodes: CompositeLit, KeyValueExpr
+	{name: "slicelit", format: "package main; var x = []any{«[]any{«»}»}", parseMultiplier: 3},      // Parser nodes: UnaryExpr, CompositeLit
+	{name: "arraylit", format: "package main; var x = «[1]any{«nil»}»", parseMultiplier: 3},         // Parser nodes: UnaryExpr, CompositeLit
+	{name: "structlit", format: "package main; var x = «struct{x any}{«nil»}»", parseMultiplier: 3}, // Parser nodes: UnaryExpr, CompositeLit
+	{name: "maplit", format: "package main; var x = «map[int]any{1:«nil»}»", parseMultiplier: 3},    // Parser nodes: CompositeLit, KeyValueExpr
+	{name: "element", format: "package main; var x = struct{x any}{x: «{«»}»}"},
 	{name: "dot", format: "package main; var x = «x.»x"},
 	{name: "index", format: "package main; var x = x«[1]»"},
 	{name: "slice", format: "package main; var x = x«[1:2]»"},