Track miniscript tree depth explicitly

Author: sanket1729

src/miniscript/mod.rs

@@ -22,7 +22,7 @@ use bitcoin::taproot::{LeafVersion, TapLeafHash};
 use self::analyzable::ExtParams;
 pub use self::context::{BareCtx, Legacy, Segwitv0, Tap};
 use crate::iter::TreeLike;
-use crate::prelude::*;
+use crate::{prelude::*, MAX_RECURSION_DEPTH};
 use crate::{script_num_size, TranslateErr};
 
 pub mod analyzable;
@@ -91,6 +91,13 @@ impl<Pk: MiniscriptKey, Ctx: ScriptContext> Miniscript<Pk, Ctx> {
             node: t,
             phantom: PhantomData,
         };
+        // TODO: This recursion depth is based on segwitv0.
+        // We can relax this in tapscript, but this should be good for almost
+        // all practical cases and we can revisit this if needed.
+        // casting to u32 is safe because tree_height will never go more than u32::MAX
+        if (res.ext.tree_height as u32) > MAX_RECURSION_DEPTH {
+            return Err(Error::MaxRecursiveDepthExceeded);
+        }
         Ctx::check_global_consensus_validity(&res)?;
         Ok(res)
     }

src/miniscript/types/extra_props.rs

@@ -140,6 +140,9 @@ pub struct ExtData {
     /// This does **not** include initial witness elements. This element only captures
     /// the additional elements that are pushed during execution.
     pub exec_stack_elem_count_dissat: Option<usize>,
+    /// The miniscript tree depth/height of this node.
+    /// Used for checking the max depth of the miniscript tree to prevent stack overflow.
+    pub tree_height: usize,
 }
 
 impl ExtData {
@@ -155,6 +158,7 @@ impl ExtData {
         timelock_info: TimelockInfo::new(),
         exec_stack_elem_count_sat: None,
         exec_stack_elem_count_dissat: Some(1),
+        tree_height: 0,
     };
 
     /// Extra data for the `1` combinator
@@ -169,6 +173,7 @@ impl ExtData {
         timelock_info: TimelockInfo::new(),
         exec_stack_elem_count_sat: Some(1),
         exec_stack_elem_count_dissat: None,
+        tree_height: 0,
     };
 }
 
@@ -204,6 +209,7 @@ impl ExtData {
             timelock_info: TimelockInfo::default(),
             exec_stack_elem_count_sat: Some(1), // pushes the pk
             exec_stack_elem_count_dissat: Some(1),
+            tree_height: 0,
         }
     }
 
@@ -226,6 +232,7 @@ impl ExtData {
             timelock_info: TimelockInfo::default(),
             exec_stack_elem_count_sat: Some(2), // dup and hash push
             exec_stack_elem_count_dissat: Some(2),
+            tree_height: 0,
         }
     }
 
@@ -250,6 +257,7 @@ impl ExtData {
             timelock_info: TimelockInfo::new(),
             exec_stack_elem_count_sat: Some(n), // n pks
             exec_stack_elem_count_dissat: Some(n),
+            tree_height: 0,
         }
     }
 
@@ -273,6 +281,7 @@ impl ExtData {
             timelock_info: TimelockInfo::new(),
             exec_stack_elem_count_sat: Some(2), // the two nums before num equal verify
             exec_stack_elem_count_dissat: Some(2),
+            tree_height: 0,
         }
     }
 
@@ -289,6 +298,7 @@ impl ExtData {
             timelock_info: TimelockInfo::new(),
             exec_stack_elem_count_sat: Some(2), // either size <32> or <hash256> <32 byte>
             exec_stack_elem_count_dissat: Some(2),
+            tree_height: 0,
         }
     }
 
@@ -305,6 +315,7 @@ impl ExtData {
             timelock_info: TimelockInfo::new(),
             exec_stack_elem_count_sat: Some(2), // either size <32> or <hash256> <32 byte>
             exec_stack_elem_count_dissat: Some(2),
+            tree_height: 0,
         }
     }
 
@@ -321,6 +332,7 @@ impl ExtData {
             timelock_info: TimelockInfo::new(),
             exec_stack_elem_count_sat: Some(2), // either size <32> or <hash256> <20 byte>
             exec_stack_elem_count_dissat: Some(2),
+            tree_height: 0,
         }
     }
 
@@ -337,6 +349,7 @@ impl ExtData {
             timelock_info: TimelockInfo::new(),
             exec_stack_elem_count_sat: Some(2), // either size <32> or <hash256> <20 byte>
             exec_stack_elem_count_dissat: Some(2),
+            tree_height: 0,
         }
     }
 
@@ -359,6 +372,7 @@ impl ExtData {
             },
             exec_stack_elem_count_sat: Some(1), // <t>
             exec_stack_elem_count_dissat: None,
+            tree_height: 0,
         }
     }
 
@@ -381,6 +395,7 @@ impl ExtData {
             },
             exec_stack_elem_count_sat: Some(1), // <t>
             exec_stack_elem_count_dissat: None,
+            tree_height: 0,
         }
     }
 
@@ -397,6 +412,7 @@ impl ExtData {
             timelock_info: self.timelock_info,
             exec_stack_elem_count_sat: self.exec_stack_elem_count_sat,
             exec_stack_elem_count_dissat: self.exec_stack_elem_count_dissat,
+            tree_height: self.tree_height + 1,
         }
     }
 
@@ -413,6 +429,7 @@ impl ExtData {
             timelock_info: self.timelock_info,
             exec_stack_elem_count_sat: self.exec_stack_elem_count_sat,
             exec_stack_elem_count_dissat: self.exec_stack_elem_count_dissat,
+            tree_height: self.tree_height + 1,
         }
     }
 
@@ -429,6 +446,7 @@ impl ExtData {
             timelock_info: self.timelock_info,
             exec_stack_elem_count_sat: self.exec_stack_elem_count_sat,
             exec_stack_elem_count_dissat: self.exec_stack_elem_count_dissat,
+            tree_height: self.tree_height + 1,
         }
     }
 
@@ -448,6 +466,7 @@ impl ExtData {
             // Even all V types push something onto the stack and then remove them
             exec_stack_elem_count_sat: self.exec_stack_elem_count_sat,
             exec_stack_elem_count_dissat: Some(1),
+            tree_height: self.tree_height + 1,
         }
     }
 
@@ -465,6 +484,7 @@ impl ExtData {
             timelock_info: self.timelock_info,
             exec_stack_elem_count_sat: self.exec_stack_elem_count_sat,
             exec_stack_elem_count_dissat: None,
+            tree_height: self.tree_height + 1,
         }
     }
 
@@ -481,6 +501,7 @@ impl ExtData {
             timelock_info: self.timelock_info,
             exec_stack_elem_count_sat: self.exec_stack_elem_count_sat,
             exec_stack_elem_count_dissat: Some(1),
+            tree_height: self.tree_height + 1,
         }
     }
 
@@ -498,6 +519,7 @@ impl ExtData {
             // Technically max(1, self.exec_stack_elem_count_sat), same rationale as cast_dupif
             exec_stack_elem_count_sat: self.exec_stack_elem_count_sat,
             exec_stack_elem_count_dissat: self.exec_stack_elem_count_dissat,
+            tree_height: self.tree_height + 1,
         }
     }
 
@@ -545,6 +567,7 @@ impl ExtData {
                 l.exec_stack_elem_count_dissat,
                 r.exec_stack_elem_count_dissat.map(|x| x + 1),
             ),
+            tree_height: 1 + cmp::max(l.tree_height, r.tree_height),
         }
     }
 
@@ -569,6 +592,7 @@ impl ExtData {
                 r.exec_stack_elem_count_sat,
             ),
             exec_stack_elem_count_dissat: None,
+            tree_height: 1 + cmp::max(l.tree_height, r.tree_height),
         }
     }
 
@@ -609,6 +633,7 @@ impl ExtData {
                 l.exec_stack_elem_count_dissat,
                 r.exec_stack_elem_count_dissat.map(|x| x + 1),
             ),
+            tree_height: 1 + cmp::max(l.tree_height, r.tree_height),
         }
     }
 
@@ -647,6 +672,7 @@ impl ExtData {
                 l.exec_stack_elem_count_dissat,
                 r.exec_stack_elem_count_dissat.map(|x| x + 1),
             ),
+            tree_height: 1 + cmp::max(l.tree_height, r.tree_height),
         }
     }
 
@@ -678,6 +704,7 @@ impl ExtData {
                 opt_max(r.exec_stack_elem_count_sat, l.exec_stack_elem_count_dissat),
             ),
             exec_stack_elem_count_dissat: None,
+            tree_height: 1 + cmp::max(l.tree_height, r.tree_height),
         }
     }
 
@@ -725,6 +752,7 @@ impl ExtData {
                 l.exec_stack_elem_count_dissat,
                 r.exec_stack_elem_count_dissat,
             ),
+            tree_height: 1 + cmp::max(l.tree_height, r.tree_height),
         }
     }
 
@@ -768,6 +796,7 @@ impl ExtData {
                 a.exec_stack_elem_count_dissat,
                 c.exec_stack_elem_count_dissat,
             ),
+            tree_height: 1 + cmp::max(a.tree_height, cmp::max(b.tree_height, c.tree_height)),
         }
     }
 
@@ -788,6 +817,7 @@ impl ExtData {
         // the max element count is same as max sat element count when satisfying one element + 1
         let mut exec_stack_elem_count_sat_vec = Vec::with_capacity(n);
         let mut exec_stack_elem_count_dissat = Some(0);
+        let mut max_child_height = 0;
 
         for i in 0..n {
             let sub = sub_ck(i);
@@ -817,6 +847,7 @@ impl ExtData {
                 .push((sub.exec_stack_elem_count_sat, sub.exec_stack_elem_count_dissat));
             exec_stack_elem_count_dissat =
                 opt_max(exec_stack_elem_count_dissat, sub.exec_stack_elem_count_dissat);
+            max_child_height = cmp::max(max_child_height, sub.tree_height);
         }
 
         stack_elem_count_sat_vec.sort_by(sat_minus_option_dissat);
@@ -887,6 +918,7 @@ impl ExtData {
             timelock_info: TimelockInfo::combine_threshold(k, timelocks),
             exec_stack_elem_count_sat,
             exec_stack_elem_count_dissat,
+            tree_height: max_child_height + 1,
         }
     }