diff --git a/crates/svg/src/lib.rs b/crates/svg/src/lib.rs index 06ae671a..d0e62c0d 100644 --- a/crates/svg/src/lib.rs +++ b/crates/svg/src/lib.rs @@ -1044,10 +1044,65 @@ pub fn parse_transform(s: &str) -> Affine { m } +/// The deepest element nesting accepted. The XML parser recurses per level and overflowed a +/// 2 MiB thread's stack (aborting the app) at a few thousand levels; real documents stay far +/// below this. +const MAX_XML_DEPTH: usize = 256; + +/// The deepest element nesting of `text` (a quick scan that skips comments, CDATA, processing +/// instructions, declarations and quoted attribute values). +fn xml_depth(text: &str) -> usize { + let b = text.as_bytes(); + let (mut i, mut depth, mut max) = (0usize, 0usize, 0usize); + let skip_to = |from: usize, end: &[u8]| b.get(from..).and_then(|r| r.windows(end.len()).position(|w| w == end)).map_or(b.len(), |p| from + p + end.len()); + while i < b.len() { + if b[i] != b'<' { + i += 1; + continue; + } + let rest = &b[i..]; + if rest.starts_with(b""); + } else if rest.starts_with(b""); + } else if rest.starts_with(b""); + } else if rest.starts_with(b""); + } else if rest.starts_with(b""); + } else { + // A start tag: find its end outside quotes; `/>` closes it at once. + let mut j = i + 1; + let mut quote = None; + while let Some(&c) = b.get(j) { + match quote { + Some(q) if c == q => quote = None, + Some(_) => {} + None if c == b'"' || c == b'\'' => quote = Some(c), + None if c == b'>' => break, + None => {} + } + j += 1; + } + if b.get(j.wrapping_sub(1)) != Some(&b'/') { + depth += 1; + max = max.max(depth); + } + i = j + 1; + } + } + max +} + /// Parse an SVG document. pub fn parse(bytes: &[u8]) -> Result { let text = String::from_utf8_lossy(bytes); let text = text.trim_start_matches('\u{feff}'); + if xml_depth(text) > MAX_XML_DEPTH { + return Err(Error::Xml(format!("elements nested more than {MAX_XML_DEPTH} levels deep"))); + } let opts = roxmltree::ParsingOptions { allow_dtd: true, ..Default::default() }; let xml = roxmltree::Document::parse_with_options(text, opts).map_err(|e| Error::Xml(e.to_string()))?; let root = xml.root_element(); diff --git a/crates/svg/src/tests.rs b/crates/svg/src/tests.rs index c367412f..a7a9bef3 100644 --- a/crates/svg/src/tests.rs +++ b/crates/svg/src/tests.rs @@ -106,3 +106,20 @@ fn transforms() { let p = m * kurbo::Point::new(0.0, 1.0); assert!((p.x - 6.0).abs() < 1e-9 && (p.y - 7.0).abs() < 1e-9); } + +#[test] +fn deep_nesting_errors_instead_of_overflowing_the_stack() { + // 100 000 nested groups overflowed the XML parser's stack and aborted the process. + let deep = |n: usize| format!("{}{}", "".repeat(n), "".repeat(n)); + assert!(matches!(crate::parse(deep(100_000).as_bytes()), Err(crate::Error::Xml(_)))); + assert!(crate::parse(deep(100).as_bytes()).is_ok()); + // Comments, CDATA, quoted '>' and self-closing tags don't count. + let s = format!( + "{}b\">{}", + "".repeat(1000), + "".repeat(1000), + "".repeat(1000) + ); + assert_eq!(crate::xml_depth(&s), 2); + assert!(crate::parse(s.as_bytes()).is_ok()); +}