Sema: fix UAF in zirClosureGet

Previously if a decl failed its capture scope would be deallocated and
set to undefined which would then lead to invalid dereference in
`zirClosureGet`. To avoid this set the capture scope to a special
failed state and fail the current decl with dependency failure if
the failed state is encountered in `zirClosureGet`.

Closes #12433
Closes #12530
Closes #12593

2 files changed, 20 insertions, 1 deletions

diff --git a/src/Module.zig b/src/Module.zig
index 3ae6c48edd..ea89225537 100644
--- a/src/Module.zig
+++ b/src/Module.zig
@@ -345,6 +345,15 @@ pub const CaptureScope = struct {
     /// During sema, this map is backed by the gpa.  Once sema completes,
     /// it is reallocated using the value_arena.
     captures: std.AutoHashMapUnmanaged(Zir.Inst.Index, TypedValue) = .{},
+
+    pub fn failed(noalias self: *const @This()) bool {
+        return self.captures.available == 0 and self.captures.size == std.math.maxInt(u32);
+    }
+
+    pub fn fail(noalias self: *@This()) void {
+        self.captures.available = 0;
+        self.captures.size = std.math.maxInt(u32);
+    }
 };
 
 pub const WipCaptureScope = struct {
@@ -383,6 +392,7 @@ pub const WipCaptureScope = struct {
     pub fn deinit(noalias self: *@This()) void {
         if (!self.finalized) {
             self.scope.captures.deinit(self.gpa);
+            self.scope.fail();
         }
         self.* = undefined;
     }
diff --git a/src/Sema.zig b/src/Sema.zig
index 8d25a7c93e..15e891ef87 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -5956,7 +5956,6 @@ fn analyzeCall(
                 error.NeededSourceLocation => {
                     _ = sema.inst_map.remove(inst);
                     const decl = sema.mod.declPtr(block.src_decl);
-                    child_block.src_decl = block.src_decl;
                     try sema.analyzeInlineCallArg(
                         block,
                         &child_block,
@@ -13740,6 +13739,16 @@ fn zirClosureGet(
     const tv = while (true) {
         // Note: We don't need to add a dependency here, because
         // decls always depend on their lexical parents.
+
+        // Fail this decl if a scope it depended on failed.
+        if (scope.failed()) {
+            if (sema.owner_func) |owner_func| {
+                owner_func.state = .dependency_failure;
+            } else {
+                sema.owner_decl.analysis = .dependency_failure;
+            }
+            return error.AnalysisFail;
+        }
         if (scope.captures.getPtr(inst_data.inst)) |tv| {
             break tv;
         }