From 4eb7bd0730d1ce37852e6d7dfeb10401e8b9acab Mon Sep 17 00:00:00 2001
From: Benjamin Koch <bbbsnowball@gmail.com>
Date: Fri, 9 Jun 2023 18:40:18 +0200
Subject: [PATCH] avoid overflow before error check
---
firmware/rust1/src/modbus_server.rs | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/firmware/rust1/src/modbus_server.rs b/firmware/rust1/src/modbus_server.rs
index bd13b5b..a9cde96 100644
--- a/firmware/rust1/src/modbus_server.rs
+++ b/firmware/rust1/src/modbus_server.rs
@@ -372,11 +372,11 @@ impl<REGS: ModbusRegisters> ModbusServer<REGS> {
let record_number = rx.read_u16be()?;
let record_length = rx.read_u16be()?;
let pos_of_length = txbuf.len();
- push(txbuf, 1 + 2 * record_length as u8)?;
- push(txbuf, ref_type)?;
- if record_length > 127 || record_length as usize * 2 > capacity - txbuf.len() {
+ if record_length > 127 || 2 + txbuf.len() + record_length as usize * 2 > capacity {
return Err(IllegalDataValue)
}
+ push(txbuf, 1 + 2 * record_length as u8)?;
+ push(txbuf, ref_type)?;
let len_before = txbuf.len();
let pusher = U16Pusher { buf: txbuf };
self.regs.read_file_record(device_addr, ref_type, file_number, record_number, record_length, pusher)?;
--
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