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[modbus_controller] Fix off-by-one bounds check in byte_from_hex_str (#15301)

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This commit is contained in:
J. Nick Koston
2026-03-30 08:57:27 -04:00
committed by GitHub
parent cd3c2ae77e
commit d420e7bc23
1 changed files with 3 additions and 3 deletions
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esphome/components/modbus_controller/modbus_controller.h
+3 -3
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@@ -81,15 +81,15 @@ inline ModbusFunctionCode modbus_register_write_function(ModbusRegisterType reg_
inline uint8_t c_to_hex(char c) { return (c >= 'A') ? (c >= 'a') ? (c - 'a' + 10) : (c - 'A' + 10) : (c - '0'); }
/** Get a byte from a hex string
* hex_byte_from_str("1122",1) returns uint_8 value 0x22 == 34
* hex_byte_from_str("1122",0) returns 0x11
* byte_from_hex_str("1122", 1) returns uint_8 value 0x22 == 34
* byte_from_hex_str("1122", 0) returns 0x11
* @param value string containing hex encoding
* @param position offset in bytes. Because each byte is encoded in 2 hex digits the position of the original byte in
* the hex string is byte_pos * 2
* @return byte value
*/
inline uint8_t byte_from_hex_str(const std::string &value, uint8_t pos) {
if (value.length() < pos * 2 + 1)
if (value.length() < pos * 2 + 2)
return 0;
return (c_to_hex(value[pos * 2]) << 4) | c_to_hex(value[pos * 2 + 1]);
}