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AP_RCProtocol: protect against invalid data in SBUS

This commit is contained in:
Andrew Tridgell 2023-10-03 20:18:40 +11:00 committed by Randy Mackay
parent c656120a6e
commit b0683ad07d
1 changed files with 16 additions and 0 deletions
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16
libraries/AP_RCProtocol/AP_RCProtocol_SBUS.cpp
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@ -131,11 +131,27 @@ bool AP_RCProtocol_SBUS::sbus_decode(const uint8_t frame[25], uint16_t *values,
/* note the number of channels decoded */ /* note the number of channels decoded */
*num_values = chancount; *num_values = chancount;
/*
as SBUS is such a weak protocol we additionally check if any of
the first 4 channels are at or below the minimum value of
875. We consider the frame as a failsafe in that case, which
means we log the data but won't use it
*/
bool invalid_data = false;
for (uint8_t i=0; i<4; i++) {
if (values[i] <= SBUS_SCALE_OFFSET) {
invalid_data = true;
}
}
/* decode and handle failsafe and frame-lost flags */ /* decode and handle failsafe and frame-lost flags */
if (frame[SBUS_FLAGS_BYTE] & (1 << SBUS_FAILSAFE_BIT)) { /* failsafe */ if (frame[SBUS_FLAGS_BYTE] & (1 << SBUS_FAILSAFE_BIT)) { /* failsafe */
/* report that we failed to read anything valid off the receiver */ /* report that we failed to read anything valid off the receiver */
*sbus_failsafe = true; *sbus_failsafe = true;
*sbus_frame_drop = true; *sbus_frame_drop = true;
} else if (invalid_data) {
*sbus_failsafe = true;
*sbus_frame_drop = false;
} else if (frame[SBUS_FLAGS_BYTE] & (1 << SBUS_FRAMELOST_BIT)) { /* a frame was lost */ } else if (frame[SBUS_FLAGS_BYTE] & (1 << SBUS_FRAMELOST_BIT)) { /* a frame was lost */
/* set a special warning flag /* set a special warning flag
* *