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Fix potential overflow in FdtWriter::begin_node() #46

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Merged
merged 3 commits into from
Oct 19, 2021
Merged

Fix potential overflow in FdtWriter::begin_node() #46

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b90841d
Fix potential overflow in FdtWriter::begin_node()
Oct 18, 2021
e393661
Limit max node depth to 64
Oct 19, 2021
a568a59
Adjust test coverage
Oct 19, 2021
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16 changes: 16 additions & 0 deletions src/writer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,8 @@ pub enum Error {
InvalidNodeName,
/// Invalid property name.
InvalidPropertyName,
/// Node depth exceeds usize::MAX
NodeDepthTooLarge,
}

impl fmt::Display for Error {
Expand All @@ -65,6 +67,7 @@ impl fmt::Display for Error {
}
Error::InvalidNodeName => write!(f, "Invalid node name"),
Error::InvalidPropertyName => write!(f, "Invalid property name"),
Error::NodeDepthTooLarge => write!(f, "Node depth exceeds usize::MAX"),
}
}
}
Expand Down Expand Up @@ -331,6 +334,10 @@ impl FdtWriter {
///
/// `name` - name of the node; must not contain any NUL bytes.
pub fn begin_node(&mut self, name: &str) -> Result<FdtWriterNode> {
if self.node_depth == usize::MAX {
return Err(Error::NodeDepthTooLarge);
}

let name_cstr = CString::new(name).map_err(|_| Error::InvalidString)?;
// The unit adddress part of the node name, if present, is not fully validated
// since the exact requirements depend on the bus mapping.
Expand All @@ -341,6 +348,8 @@ impl FdtWriter {
self.append_u32(FDT_BEGIN_NODE);
self.data.extend(name_cstr.to_bytes_with_nul());
self.align(4);
// This can not overflow due to the `if` at the beginning of the function
// where the current depth is checked against usize::MAX.
self.node_depth += 1;
self.node_ended = false;
Ok(FdtWriterNode {
Expand Down Expand Up @@ -1095,4 +1104,11 @@ mod tests {
// Name too long.
assert!(!property_name_valid("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"));
}

#[test]
fn depth_overflow() {
let mut fdt = FdtWriter::new().unwrap();
fdt.node_depth = usize::MAX;
assert_eq!(fdt.begin_node("").unwrap_err(), Error::NodeDepthTooLarge);
}
}