fix(derive_key_from_path): check length of current_key_material

[DeckerSU]

The derive_key_from_path function:

komodo-defi-framework/mm2src/crypto/src/key_derivation.rs

Lines 135 to 152 in a7ffbb1

	fn derive_key_from_path(master_node: &[u8], path: &str) -> MmResult<[u8; 32], KeyDerivationError> {
	let mut current_key_material = master_node.to_vec();
	for segment in path.split('/').filter(|s| !s.is_empty()) {
	let mut mac = HmacSha512::new_from_slice(&current_key_material[..32])
	.map_err(|_| KeyDerivationError::HmacInitialization)?;
	mac.update(b"\x00");
	mac.update(segment.as_bytes());
	drop_mutability!(mac);
	let hmac_result = mac.finalize().into_bytes();
	current_key_material = hmac_result.to_vec();
	}
	drop_mutability!(current_key_material);
	current_key_material[32..64]
	.try_into()
	.map_to_mm(|_| KeyDerivationError::InvalidKeyLength)
	}

could potentially lead to a panic if the master_node length is not 64.

For example, calling it like this:

let master_node = [0u8; 32];
let result = derive_key_from_path(&master_node, "");

In this case, since the loop over path will not be executed, current_key_material remains unchanged, and attempting to slice current_key_material[32..64] will cause a panic.

Another potential panic occurs when attempting to slice current_key_material[..32] if master_node has a length below 32.

Possible Solution

A simple fix for both cases is to check the length before proceeding:

if current_key_material.len() < 64 {
    return MmError::err(KeyDerivationError::InvalidKeyLength);
}

This would prevent panics and ensure safer execution.