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openSAFETY: Fix various heuristic bugs 

- Wrong true-positives if the frame got wrongly detected

Change-Id: Ifaaec601bde260f8a38c61aad1e5e79b16003c60
Reviewed-on: https://code.wireshark.org/review/9123
Reviewed-by: Roland Knall <rknall@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>
This commit is contained in:
Roland Knall 2015-06-25 11:29:59 +02:00 committed by Anders Broman
parent 8f40e2cd8d
commit fe679bfa5d
1 changed files with 36 additions and 13 deletions
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49
epan/dissectors/packet-opensafety.c
View File

@ -478,7 +478,7 @@ findFrame1Position ( tvbuff_t *message_tvb, guint16 byte_offset, guint8 dataLeng
return i_wFrame1Position;
}
static guint8 findSafetyFrame ( tvbuff_t *message_tvb, guint u_Offset, gboolean b_frame2first,
static gboolean findSafetyFrame ( tvbuff_t *message_tvb, guint u_Offset, gboolean b_frame2first,
guint *u_frameOffset, guint *u_frameLength, opensafety_packet_info *packet )
{
guint ctr, rem_length;
@ -488,11 +488,14 @@ static guint8 findSafetyFrame ( tvbuff_t *message_tvb, guint u_Offset, gboolean
guint b_ID;
gboolean found;
found = 0;
found = FALSE;
ctr = u_Offset;
rem_length = tvb_reported_length_remaining (message_tvb, ctr);
while ( packet != NULL && rem_length >= OSS_MINIMUM_LENGTH)
/* Search will allways start at the second byte of the frame ( cause it determines )
* the type of package and therefore everything else. Therefore the mininmum length - 1
* is the correct minimum length */
while ( packet != NULL && rem_length >= ( OSS_MINIMUM_LENGTH - 1 ) )
{
/* The ID byte must ALWAYS be the second byte, therefore 0 is invalid,
* also, the byte we want to access, must at least exist, otherwise,
@ -596,7 +599,7 @@ static guint8 findSafetyFrame ( tvbuff_t *message_tvb, guint u_Offset, gboolean
f2crc = tvb_get_letohs ( message_tvb, ctr + 3 + 5 + b_Length );
if ( crc != f2crc )
{
found = 1;
found = TRUE;
break;
}
}
@ -606,12 +609,31 @@ static guint8 findSafetyFrame ( tvbuff_t *message_tvb, guint u_Offset, gboolean
*u_frameLength = 2 * b_Length + 2 * crcOffset + 11;
*u_frameOffset = ( ctr - 1 );
/* At this point frames had been checked for SoC and SoA types of
* EPL. This is no longer necessary and leads to false-negatives.
* SoC and SoA frames get filtered out at the EPL entry point, cause
* EPL only provides payload, no longer complete frames. */
found = 1;
break;
/* If the first crc is zero, the second one must not be 0. The header
* for each subfields differ, therefore it is impossible, that both
* crcs are zero */
if ( crc == 0 )
{
f2crc = tvb_get_guint8 ( message_tvb, ( ctr - 1 ) + 10 + ( 2 * b_Length ) );
if ( b_Length > 8 )
f2crc = tvb_get_letohs ( message_tvb, ( ctr - 1 ) + 11 + ( 2 * b_Length ) );
/* The crc's differ, everything is ok */
if ( crc != f2crc )
{
found = TRUE;
break;
}
}
else
{
/* At this point frames had been checked for SoC and SoA types of
* EPL. This is no longer necessary and leads to false-negatives.
* SoC and SoA frames get filtered out at the EPL entry point, cause
* EPL only provides payload, no longer complete frames. */
found = TRUE;
break;
}
}
}
}
@ -678,7 +700,7 @@ static guint8 findSafetyFrame ( tvbuff_t *message_tvb, guint u_Offset, gboolean
if ( b_frame2first && found )
*u_frameOffset = u_Offset;
return (found ? 1 : 0);
return found;
}
static gint
@ -1903,8 +1925,9 @@ opensafety_package_dissector(const gchar *protocolName, const gchar *sub_diss_ha
/* Reset the next_tvb buffer */
next_tvb = NULL;
/* Smallest possible frame size is 11 */
if ( tvb_captured_length_remaining(message_tvb, frameOffset ) < OSS_MINIMUM_LENGTH )
/* Smallest possible frame size is 11, but this check must ensure, that even the last frame
* will get considered, which leads us with 10, as the first byte checked is the second one */
if ( tvb_captured_length_remaining(message_tvb, frameOffset ) < ( OSS_MINIMUM_LENGTH - 1 ) )
break;
/* Resetting packet, to ensure, that findSafetyFrame starts with a fresh frame.