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Sanity Check on msglen after decoding

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Add a sanity check to ensure that msglen is consistent with the DF type.
This commit is contained in:
Malcolm Robb 2013-04-30 10:32:23 +01:00
parent 5f7ed42050
commit 8d65abd317
1 changed files with 22 additions and 20 deletions
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42
dump1090.c
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@ -56,7 +56,7 @@
// MinorVer changes when additional features are added, but not for bug fixes (range 00-99)
// DayDate & Year changes for all changes, including for bug fixes. It represent the release date of the update
//
#define MODES_DUMP1090_VERSION "1.04.2904.13"
#define MODES_DUMP1090_VERSION "1.04.3004.13"
#define MODES_DEFAULT_RATE 2000000
#define MODES_DEFAULT_FREQ 1090000000
@ -1972,25 +1972,27 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
}
}
if (msglen == modesMessageLenByType(theByte = msg[0])) {
// The msglen is consistent with the DF type
if ((errorsTy == 1) && (theErrs & 0x78)) {
// We guessed at one of the message type bits. See if our guess is "likely"
// to be correct by comparing the DF against a list of known good DF's
int DF = ((theByte = msg[0]) >> 3) & 0x1f;
if ( (DF != 0) && (DF != 4) && (DF != 5) && (DF != 11)
&& (DF != 16) && (DF != 17) && (DF != 18) && (DF != 19) && (DF != 20) && (DF != 21) && (DF != 22) && (DF != 24) ) {
// Other DF values are probably errors. Toggle the bit we guessed at and see if the resultant DF is more likely
theByte ^= theErrs;
DF = (theByte >> 3) & 0x1f;
// if this DF any more likely??
if ( (DF == 0) || (DF == 4) || (DF == 5) || (DF == 11)
|| (DF == 16) || (DF == 17) || (DF == 18) || (DF == 19) || (DF == 20) || (DF == 21) || (DF == 22) || (DF == 24) ) {
// Yep, more likely, so update the main message
msg[0] = theByte;
Modes.stat_DF_Type_Corrected++;
errors--; // decrease the error count so we attempt to use the modified DF.
}
// Ensure msglen is consistent with the DF type
i = modesMessageLenByType(msg[0] >> 3);
if (msglen > i) {msglen = i;}
else if (msglen < i) {msglen = 0;}
if ((msglen) && (errorsTy == 1) && (theErrs & 0x78)) {
// We guessed at one of the message type bits. See if our guess is "likely"
// to be correct by comparing the DF against a list of known good DF's
int DF = ((theByte = msg[0]) >> 3) & 0x1f;
if ( (DF != 0) && (DF != 4) && (DF != 5) && (DF != 11)
&& (DF != 16) && (DF != 17) && (DF != 18) && (DF != 19) && (DF != 20) && (DF != 21) && (DF != 22) && (DF != 24) ) {
// Other DF values are probably errors. Toggle the bit we guessed at and see if the resultant DF is more likely
theByte ^= theErrs;
DF = (theByte >> 3) & 0x1f;
// if this DF any more likely??
if ( (DF == 0) || (DF == 4) || (DF == 5) || (DF == 11)
|| (DF == 16) || (DF == 17) || (DF == 18) || (DF == 19) || (DF == 20) || (DF == 21) || (DF == 22) || (DF == 24) ) {
// Yep, more likely, so update the main message
msg[0] = theByte;
Modes.stat_DF_Type_Corrected++;
errors--; // decrease the error count so we attempt to use the modified DF.
}
}
}