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Limit nesting depth by default to guard against stack overflow #16

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950acfc
limit nesting depth by default to guard against stack overflow
spyoungtech May 23, 2025
3d2aaa5
add depth protection to unary
spyoungtech May 26, 2025
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6 changes: 5 additions & 1 deletion Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,9 @@ unicode-general-category = { version = "1.0" }
[features]
default = ["serde"]
serde = ["dep:serde"]
unlimited_depth = []



[dev-dependencies.serde]
version = "1.0"
Expand Down Expand Up @@ -49,4 +52,5 @@ name = "json5-trailing-comma-formatter"
test = true

[package.metadata.docs.rs]
all-features = true
all-features = true

42 changes: 40 additions & 2 deletions src/parser.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -251,12 +251,19 @@ struct JSON5Parser<'toks, 'input> {
source: &'input str,
source_tokens: Peekable<Iter<'toks, TokenSpan>>,
lookahead: Option<&'toks TokenSpan>,
current_depth: usize,
max_depth: usize,
}


impl<'toks, 'input> JSON5Parser<'toks, 'input> {
fn new(tokens: &'toks Tokens<'input>) -> Self {
JSON5Parser { source_tokens: tokens.tok_spans.iter().peekable(), lookahead: None, source: tokens.source }
use crate::utils::MAX_DEPTH;
JSON5Parser { source_tokens: tokens.tok_spans.iter().peekable(), lookahead: None, source: tokens.source, current_depth: 0, max_depth: MAX_DEPTH }
}

fn with_max_depth(tokens: &'toks Tokens<'input>, max_depth: usize) -> Self {
JSON5Parser { source_tokens: tokens.tok_spans.iter().peekable(), lookahead: None, source: tokens.source, current_depth: 0, max_depth: max_depth }
}

fn advance(&mut self) -> Option<&'toks TokenSpan> {
Expand Down Expand Up @@ -487,6 +494,11 @@ impl<'toks, 'input> JSON5Parser<'toks, 'input> {
match self.check_and_consume(vec![TokType::Plus, TokType::Minus]) {
None => self.parse_primary(),
Some(span) => {
self.current_depth = self.current_depth + 1;
if self.current_depth > self.max_depth {
let idx = self.position();
return Err(self.make_error(format!("max depth ({}) exceeded while parsing unary. To expand the depth, use the ``with_max_depth`` constructor or enable the `unlimited_depth` feature", self.max_depth), idx))
}
match span.1 {
TokType::Plus => {
let value = self.parse_unary()?;
Expand All @@ -496,6 +508,7 @@ impl<'toks, 'input> JSON5Parser<'toks, 'input> {
return Err(self.make_error(format!("Unary operations not allowed for value {:?}", val), span.2))
}
}
self.current_depth = self.current_depth - 1;
Ok(JSONValue::Unary {operator: UnaryOperator::Plus, value: Box::new(value)})
}
TokType::Minus => {
Expand All @@ -506,6 +519,7 @@ impl<'toks, 'input> JSON5Parser<'toks, 'input> {
return Err(self.make_error(format!("Unary operations not allowed for value {:?}", val), span.2))
}
}
self.current_depth = self.current_depth - 1;
Ok(JSONValue::Unary {operator: UnaryOperator::Minus, value: Box::new(value)})
}
_ => unreachable!("no")
Expand All @@ -529,7 +543,14 @@ impl<'toks, 'input> JSON5Parser<'toks, 'input> {


fn parse_value(&mut self) -> Result<JSONValue<'input>, ParsingError> {
self.parse_obj_or_array()
self.current_depth = self.current_depth + 1;
if self.current_depth > self.max_depth {
let idx = self.position();
return Err(self.make_error(format!("max depth ({}) exceeded in nested arrays/objects. To expand the depth, use the ``with_max_depth`` constructor or enable the `unlimited_depth` feature", self.max_depth), idx))
}
let res = self.parse_obj_or_array();
self.current_depth = self.current_depth - 1;
res
}

fn parse_text(&mut self) -> Result<JSONText<'input>, ParsingError> {
Expand Down Expand Up @@ -606,6 +627,23 @@ mod tests {
assert!(res.is_err());
}

#[cfg(not(feature = "unlimited_depth"))]
#[test]
fn test_deeply_nested() {
let n = 4000;
let mut s = String::with_capacity(n * 2);
for _ in 0 .. n {
s.push('[')
}
for _ in 0 .. n {
s.push(']')
}
let res = from_str(s.as_str());
assert!(res.is_err());
assert!(res.unwrap_err().message.contains("max depth"))
}


#[test]
fn test_from_bytes() {
let res = from_bytes(b"{}").unwrap();
Expand Down
42 changes: 39 additions & 3 deletions src/rt/parser.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -334,12 +334,19 @@ struct JSON5Parser<'toks, 'input> {
source: &'input str,
source_tokens: Peekable<Iter<'toks, TokenSpan>>,
lookahead: Option<&'toks TokenSpan>,
current_depth: usize,
max_depth: usize,
}


impl<'toks, 'input> JSON5Parser<'toks, 'input> {
fn new(tokens: &'toks Tokens<'input>) -> Self {
JSON5Parser { source_tokens: tokens.tok_spans.iter().peekable(), lookahead: None, source: tokens.source }
use crate::utils::MAX_DEPTH;
JSON5Parser { source_tokens: tokens.tok_spans.iter().peekable(), lookahead: None, source: tokens.source, current_depth: 0, max_depth: MAX_DEPTH }
}

fn with_max_depth(&mut self, tokens: &'toks Tokens<'input>, max_depth: usize) -> Self {
JSON5Parser { source_tokens: tokens.tok_spans.iter().peekable(), lookahead: None, source: tokens.source, current_depth: 0, max_depth: max_depth }
}

fn advance(&mut self) -> Option<&'toks TokenSpan> {
Expand Down Expand Up @@ -602,6 +609,11 @@ impl<'toks, 'input> JSON5Parser<'toks, 'input> {
match self.check_and_consume(vec![TokType::Plus, TokType::Minus]) {
None => self.parse_primary(),
Some(span) => {
self.current_depth = self.current_depth + 1;
if self.current_depth > self.max_depth {
let idx = self.position();
return Err(self.make_error(format!("max depth ({}) exceeded while parsing unary. To expand the depth, use the ``with_max_depth`` constructor or enable the `unlimited_depth` feature", self.max_depth), idx))
}
match span.1 {
TokType::Plus => {
let value = self.parse_unary()?;
Expand All @@ -611,7 +623,7 @@ impl<'toks, 'input> JSON5Parser<'toks, 'input> {
return Err(self.make_error(format!("Unary operations not allowed for value {:?}", val), span.2))
}
}

self.current_depth = self.current_depth - 1;
Ok(JSONValue::Unary {operator: UnaryOperator::Plus, value: Box::new(value)})
}
TokType::Minus => {
Expand All @@ -622,6 +634,7 @@ impl<'toks, 'input> JSON5Parser<'toks, 'input> {
return Err(self.make_error(format!("Unary operations not allowed for value {:?}", val), span.2))
}
}
self.current_depth = self.current_depth - 1;
Ok(JSONValue::Unary {operator: UnaryOperator::Minus, value: Box::new(value)})
}
_ => unreachable!("no")
Expand All @@ -645,7 +658,14 @@ impl<'toks, 'input> JSON5Parser<'toks, 'input> {


fn parse_value(&mut self) -> Result<JSONValue, ParsingError> {
self.parse_obj_or_array()
self.current_depth = self.current_depth + 1;
if self.current_depth > self.max_depth {
let idx = self.position();
return Err(self.make_error(format!("max depth ({}) exceeded in nested arrays/objects. To expand the depth, use the ``with_max_depth`` constructor or enable the `unlimited_depth` feature", self.max_depth), idx))
}
let res = self.parse_obj_or_array();
self.current_depth = self.current_depth - 1;
res
}

fn parse_text(&mut self) -> Result<JSONText, ParsingError> {
Expand Down Expand Up @@ -713,6 +733,22 @@ mod tests {
assert!(res.is_err());
}

#[cfg(not(feature = "unlimited_depth"))]
#[test]
fn test_deeply_nested() {
let n = 4000;
let mut s = String::with_capacity(n * 2);
for _ in 0 .. n {
s.push('[')
}
for _ in 0 .. n {
s.push(']')
}
let res = crate::parser::from_str(s.as_str());
assert!(res.is_err());
assert!(res.unwrap_err().message.contains("max depth"))
}

#[test]
fn test_foo() {
let res = from_str("{}").unwrap();
Expand Down
19 changes: 18 additions & 1 deletion src/utils.rs
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Expand Up @@ -158,4 +158,21 @@ fn char_from_u32(u: u32) -> Result<char, String> {

fn err<S: Into<String>>(message: S) -> String {
message.into()
}
}


#[cfg(all(not(feature = "unlimited_depth"), not(target_os = "windows"), debug_assertions))]
pub (crate) const MAX_DEPTH: usize = 1000;

#[cfg(all(not(feature = "unlimited_depth"), not(target_os = "windows"), not(debug_assertions)))]
pub (crate) const MAX_DEPTH: usize = 3000;


#[cfg(all(not(feature = "unlimited_depth"), target_os = "windows", debug_assertions))]
pub (crate) const MAX_DEPTH: usize = 700;

#[cfg(all(not(feature = "unlimited_depth"), target_os = "windows", not(debug_assertions)))]
pub (crate) const MAX_DEPTH: usize = 2000;

#[cfg(feature = "unlimited_depth")]
pub (crate) const MAX_DEPTH: usize = usize::MAX;