Fix seg fault if popping from empty stack (L-system trees)

See: https://github.com/minetest/minetest/issues/1525

Background
Wuzzy2: If you attempt to spawn a L-system tree with minetest.spawn_tree, you can make Minetest crash if it is attempted to pop an empty stack.

ShadowNinja: This shouldn't cause a segmentation fault, but it should throw a Lua error

Commit Description
This commit throws a Lua error instead of causing a segmentation fault. The server will still "crash" but will include a Lua backtrace.

L-Systems fix randomness
Unless a random seed is provided (via Lua treedef) seed the PRNG with a different seed for each tree
Resolves: https://github.com/minetest/minetest/issues/1469

Fix l-system crash when treedef random_level not set by Lua

diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index 74487edee4d0344fd689d7b5c816e4d4fee8465c..5412c4ccb61bbfd5904b8062566b9054fddb131f 100644 (file)
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -2208,7 +2208,7 @@ treedef={
   thin_branches, - boolean true -> use thin (1 node) branches
   fruit,         - string  fruit node name
   fruit_chance,  - num     chance (0-100) to replace leaves with fruit node
-  seed,          - num     random seed
+  seed,          - num     random seed; if no seed is provided, the engine will create one
   }
 
 Key for Special L-System Symbols used in Axioms

diff --git a/src/script/lua_api/l_env.cpp b/src/script/lua_api/l_env.cpp
index e6ca846d8bc1f4bc81d15f078d57b18e0bc9c195..deeb5966f572fb74e44d17293b7b875320d6bf79 100644 (file)
--- a/src/script/lua_api/l_env.cpp
+++ b/src/script/lua_api/l_env.cpp
@@ -747,7 +747,8 @@ int ModApiEnvMod::l_spawn_tree(lua_State *L)
                }
                getintfield(L, 2, "angle", tree_def.angle);
                getintfield(L, 2, "iterations", tree_def.iterations);
-               getintfield(L, 2, "random_level", tree_def.iterations_random_level);
+               if (!getintfield(L, 2, "random_level", tree_def.iterations_random_level))
+                       tree_def.iterations_random_level = 0;
                getstringfield(L, 2, "trunk_type", tree_def.trunk_type);
                getboolfield(L, 2, "thin_branches", tree_def.thin_branches);
                tree_def.fruit_chance=0;
@@ -757,11 +758,20 @@ int ModApiEnvMod::l_spawn_tree(lua_State *L)
                        tree_def.fruitnode=ndef->getId(fruit);
                        getintfield(L, 2, "fruit_chance",tree_def.fruit_chance);
                }
-               getintfield(L, 2, "seed", tree_def.seed);
+               tree_def.explicit_seed = getintfield(L, 2, "seed", tree_def.seed);
        }
        else
                return 0;
-       treegen::spawn_ltree (env, p0, ndef, tree_def);
+
+       treegen::error e;
+       if ((e = treegen::spawn_ltree (env, p0, ndef, tree_def)) != treegen::SUCCESS) {
+               if (e == treegen::UNBALANCED_BRACKETS) {
+                       luaL_error(L, "spawn_tree(): closing ']' has no matching opening bracket");
+               } else {
+                       luaL_error(L, "spawn_tree(): unknown error");
+               }
+       }
+
        return 1;
 }
 

diff --git a/src/treegen.cpp b/src/treegen.cpp
index 542bdf21c10305855dddde769d17b40ed5a2a010..bd4a2f2c9b9760d0a439f8b9f63922e32907b864 100644 (file)
--- a/src/treegen.cpp
+++ b/src/treegen.cpp
@@ -118,14 +118,19 @@ void make_tree(ManualMapVoxelManipulator &vmanip, v3s16 p0,
 }
 
 // L-System tree LUA spawner
-void spawn_ltree(ServerEnvironment *env, v3s16 p0, INodeDefManager *ndef, TreeDef tree_definition)
+treegen::error spawn_ltree(ServerEnvironment *env, v3s16 p0, INodeDefManager *ndef, TreeDef tree_definition)
 {
        ServerMap *map = &env->getServerMap();
        std::map<v3s16, MapBlock*> modified_blocks;
        ManualMapVoxelManipulator vmanip(map);
        v3s16 tree_blockp = getNodeBlockPos(p0);
+       treegen::error e;
+
        vmanip.initialEmerge(tree_blockp - v3s16(1,1,1), tree_blockp + v3s16(1,3,1));
-       make_ltree (vmanip, p0, ndef, tree_definition);
+       e = make_ltree (vmanip, p0, ndef, tree_definition);
+       if (e != SUCCESS)
+               return e;
+
        vmanip.blitBackAll(&modified_blocks);
 
        // update lighting
@@ -142,15 +147,25 @@ void spawn_ltree(ServerEnvironment *env, v3s16 p0, INodeDefManager *ndef, TreeDe
                event.modified_blocks.insert(i->first);
        }
        map->dispatchEvent(&event);
+       return SUCCESS;
 }
 
 //L-System tree generator
-void make_ltree(ManualMapVoxelManipulator &vmanip, v3s16 p0, INodeDefManager *ndef,
+treegen::error make_ltree(ManualMapVoxelManipulator &vmanip, v3s16 p0, INodeDefManager *ndef,
                TreeDef tree_definition)
 {
        MapNode dirtnode(ndef->getId("mapgen_dirt"));
+       int seed;
+       if (tree_definition.explicit_seed)
+       {
+               seed = tree_definition.seed+14002;
+       }
+       else
+       {
+               seed = p0.X*2 + p0.Y*4 + p0.Z;      // use the tree position to seed PRNG
+       }
+       PseudoRandom ps(seed);
 
-       PseudoRandom ps(tree_definition.seed+14002);
        // chance of inserting abcd rules
        double prop_a = 9;
        double prop_b = 8;
@@ -354,6 +369,8 @@ void make_ltree(ManualMapVoxelManipulator &vmanip, v3s16 p0, INodeDefManager *nd
                        stack_position.push(position);
                        break;
                case ']':
+                       if (stack_orientation.empty())
+                               return UNBALANCED_BRACKETS;
                        rotation=stack_orientation.top();
                        stack_orientation.pop();
                        position=stack_position.top();
@@ -393,6 +410,8 @@ void make_ltree(ManualMapVoxelManipulator &vmanip, v3s16 p0, INodeDefManager *nd
                        break;
                }
        }
+
+       return SUCCESS;
 }
 
 void tree_node_placement(ManualMapVoxelManipulator &vmanip, v3f p0,

diff --git a/src/treegen.h b/src/treegen.h
index 55da6f9e5bd6e014fee2e3b92843406c20977084..a557ad97516fca2e77625576901fb31a1b2436b9 100644 (file)
--- a/src/treegen.h
+++ b/src/treegen.h
@@ -30,6 +30,11 @@ class ServerEnvironment;
 
 namespace treegen {
 
+       enum error {
+               SUCCESS,
+               UNBALANCED_BRACKETS
+       };
+
        struct TreeDef {
                std::string initial_axiom;
                std::string rules_a;
@@ -50,6 +55,7 @@ namespace treegen {
                MapNode fruitnode;
                int fruit_chance;
                int seed;
+               bool explicit_seed;
        };
 
        // Add default tree
@@ -60,10 +66,10 @@ namespace treegen {
                INodeDefManager *ndef, int seed);
 
        // Add L-Systems tree (used by engine)
-       void make_ltree(ManualMapVoxelManipulator &vmanip, v3s16 p0, INodeDefManager *ndef,
+       treegen::error make_ltree(ManualMapVoxelManipulator &vmanip, v3s16 p0, INodeDefManager *ndef,
                TreeDef tree_definition);
        // Spawn L-systems tree from LUA
-       void spawn_ltree (ServerEnvironment *env, v3s16 p0, INodeDefManager *ndef,
+       treegen::error spawn_ltree (ServerEnvironment *env, v3s16 p0, INodeDefManager *ndef,
                TreeDef tree_definition);
 
        // L-System tree gen helper functions