Add recursion limit

Author: chipshort

Cargo.lock

@@ -15,7 +15,7 @@ license = "MIT OR Apache-2.0"
 name = "serde-json-wasm"
 readme = "README.md"
 repository = "https://github.com/CosmWasm/serde-json-wasm"
-version = "1.0.0"
+version = "1.0.1"
 exclude = [
     ".cargo/",
     ".github/",

Cargo.toml

@@ -75,6 +75,9 @@ pub enum Error {
     /// JSON has a comma after the last value in an array or map.
     TrailingComma,
 
+    /// JSON is nested too deeply, exceeeded the recursion limit.
+    RecursionLimitExceeded,
+
     /// Custom error message from serde
     Custom(String),
 }
@@ -128,6 +131,7 @@ impl core::fmt::Display for Error {
                      value."
                 }
                 Error::TrailingComma => "JSON has a comma after the last value in an array or map.",
+                Error::RecursionLimitExceeded => "JSON is nested too deeply, exceeeded the recursion limit.",
                 Error::Custom(msg) => msg,
             }
         )

src/de/errors.rs

@@ -21,6 +21,9 @@ use self::seq::SeqAccess;
 pub struct Deserializer<'b> {
     slice: &'b [u8],
     index: usize,
+
+    /// Remaining depth until we hit the recursion limit
+    remaining_depth: u8,
 }
 
 enum StringLike<'a> {
@@ -30,7 +33,11 @@ enum StringLike<'a> {
 
 impl<'a> Deserializer<'a> {
     fn new(slice: &'a [u8]) -> Deserializer<'_> {
-        Deserializer { slice, index: 0 }
+        Deserializer {
+            slice,
+            index: 0,
+            remaining_depth: 128,
+        }
     }
 
     fn eat_char(&mut self) {
@@ -287,16 +294,22 @@ impl<'a, 'de> de::Deserializer<'de> for &'a mut Deserializer<'de> {
                 }
             }
             b'[' => {
-                self.eat_char();
-                let ret = visitor.visit_seq(SeqAccess::new(self))?;
+                check_recursion! {
+                    self.eat_char();
+                    let ret = visitor.visit_seq(SeqAccess::new(self));
+                }
+                let ret = ret?;
 
                 self.end_seq()?;
 
                 Ok(ret)
             }
             b'{' => {
-                self.eat_char();
-                let ret = visitor.visit_map(MapAccess::new(self))?;
+                check_recursion! {
+                    self.eat_char();
+                    let ret = visitor.visit_map(MapAccess::new(self));
+                }
+                let ret = ret?;
 
                 self.end_map()?;
 
@@ -513,8 +526,11 @@ impl<'a, 'de> de::Deserializer<'de> for &'a mut Deserializer<'de> {
     {
         match self.parse_whitespace().ok_or(Error::EofWhileParsingValue)? {
             b'[' => {
-                self.eat_char();
-                let ret = visitor.visit_seq(SeqAccess::new(self))?;
+                check_recursion! {
+                    self.eat_char();
+                    let ret = visitor.visit_seq(SeqAccess::new(self));
+                }
+                let ret = ret?;
 
                 self.end_seq()?;
 
@@ -550,9 +566,11 @@ impl<'a, 'de> de::Deserializer<'de> for &'a mut Deserializer<'de> {
         let peek = self.parse_whitespace().ok_or(Error::EofWhileParsingValue)?;
 
         if peek == b'{' {
-            self.eat_char();
-
-            let ret = visitor.visit_map(MapAccess::new(self))?;
+            check_recursion! {
+                self.eat_char();
+                let ret = visitor.visit_map(MapAccess::new(self));
+            }
+            let ret = ret?;
 
             self.end_map()?;
 
@@ -588,8 +606,11 @@ impl<'a, 'de> de::Deserializer<'de> for &'a mut Deserializer<'de> {
             b'"' => visitor.visit_enum(UnitVariantAccess::new(self)),
             // if it is a struct enum
             b'{' => {
-                self.eat_char();
-                visitor.visit_enum(StructVariantAccess::new(self))
+                check_recursion! {
+                    self.eat_char();
+                    let value = visitor.visit_enum(StructVariantAccess::new(self));
+                }
+                value
             }
             _ => Err(Error::ExpectedSomeIdent),
         }
@@ -649,6 +670,20 @@ where
     from_slice(s.as_bytes())
 }
 
+macro_rules! check_recursion {
+    ($this:ident $($body:tt)*) => {
+        $this.remaining_depth -= 1;
+        if $this.remaining_depth == 0 {
+            return Err($crate::de::Error::RecursionLimitExceeded);
+        }
+
+        $this $($body)*
+
+        $this.remaining_depth += 1;
+    };
+}
+pub(crate) use check_recursion;
+
 #[cfg(test)]
 mod tests {
     use super::from_str;

src/de/mod.rs

@@ -227,4 +227,29 @@ mod test {
             item
         );
     }
+
+    #[test]
+    fn no_stack_overflow() {
+        const AMOUNT: usize = 2000;
+        let mut json = String::from(r#"{"":"#);
+
+        #[derive(Debug, Deserialize, Serialize)]
+        pub struct Person {
+            name: String,
+            age: u8,
+            phones: Vec<String>,
+        }
+
+        for _ in 0..AMOUNT {
+            json.push('[');
+        }
+        for _ in 0..AMOUNT {
+            json.push(']');
+        }
+
+        json.push_str(r#"]        }[[[[[[[[[[[[[[[[[[[[[   ""","age":35,"phones":["#);
+
+        let err = from_str::<Person>(&json).unwrap_err();
+        assert_eq!(err, crate::de::Error::RecursionLimitExceeded);
+    }
 }