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Harden FS20/FHT and disable it by default

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Command codes 0x1c-0x1f are documented as unused ("frei") and never
sent by real devices, so accepting them only widened the false-decode
surface for foreign bitstreams that happen to pass parity and the
checksum band.
This commit is contained in:
Benjamin Larsson
2026-07-22 02:49:05 +02:00
parent 30783dae84
commit 4ff81dd03a
3 changed files with 11 additions and 2 deletions
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2
README.md
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@@ -210,7 +210,7 @@ See [CONTRIBUTING.md](./docs/CONTRIBUTING.md).
[119] Bresser Weather Center 5-in-1
[120] Digitech XC-0324 / AmbientWeather FT005TH temp/hum sensor
[121] Opus/Imagintronix XT300 Soil Moisture
[122] FS20 / FHT
[122]* FS20 / FHT
[123]* Jansite TPMS Model TY02S
[124] LaCrosse/ELV/Conrad WS7000/WS2500 weather sensors
[125] TS-FT002 Wireless Ultrasonic Tank Liquid Level Meter With Temperature Sensor

2
conf/rtl_433.example.conf
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@@ -361,7 +361,7 @@ convert si
protocol 119 # Bresser Weather Center 5-in-1
protocol 120 # Digitech XC-0324 / AmbientWeather FT005TH temp/hum sensor
protocol 121 # Opus/Imagintronix XT300 Soil Moisture
protocol 122 # FS20 / FHT
# protocol 122 # FS20 / FHT
# protocol 123 # Jansite TPMS Model TY02S
protocol 124 # LaCrosse/ELV/Conrad WS7000/WS2500 weather sensors
protocol 125 # TS-FT002 Wireless Ultrasonic Tank Liquid Level Meter With Temperature Sensor

9
src/devices/fs20.c
View File

@@ -20,6 +20,8 @@ enum {
FS20_BASE_FRAME_BITS = FS20_BASE_BYTES * FS20_PARITY_BYTE_BITS,
FS20_EXT_FRAME_BITS = FS20_EXT_BYTES * FS20_PARITY_BYTE_BITS,
FS20_EXT_FLAG = 0x20,
FS20_CMD_MASK = 0x1f,
FS20_CMD_RESERVED_MIN = 0x1c, // 0x1c-0x1f ("frei"/unused) never sent by real devices
FHT_CMD_MASK = 0x0f,
FHT_CMD_END_OF_SYNC = 0x00,
};
@@ -277,6 +279,12 @@ static int fs20_decode(r_device *decoder, bitbuffer_t *bitbuffer)
return DECODE_FAIL_SANITY;
}
// FS20 command codes 0x1c-0x1f are documented as unused/reserved and
// never sent by real devices; a foreign bitstream is the likelier source.
if (is_fs20 && (cmd & FS20_CMD_MASK) >= FS20_CMD_RESERVED_MIN) {
return DECODE_FAIL_SANITY;
}
// A real FS20 housecode is a user-set DIP-switch code, effectively
// uniform over the whole address space; an all-zero housecode and
// address is a degenerate pattern that mainly shows up when foreign
@@ -334,4 +342,5 @@ r_device const fs20 = {
.reset_limit = 9000,
.decode_fn = &fs20_decode,
.fields = output_fields,
.disabled = 1, // false decodes from foreign bitstreams, see issue #3611
};