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ulDNSHandlePacket() - check length before calculating payload size #1615

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Dec 13, 2019
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ulDNSHandlePacket() - check length before calculating payload size #1615

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31 changes: 19 additions & 12 deletions libraries/freertos_plus/standard/freertos_plus_tcp/source/FreeRTOS_DNS.c
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Original file line number Diff line number Diff line change
Expand Up @@ -916,18 +916,25 @@ for testing purposes, by the module iot_test_freertos_tcp.c
uint32_t ulDNSHandlePacket( NetworkBufferDescriptor_t *pxNetworkBuffer )
{
DNSMessage_t *pxDNSMessageHeader;
size_t uxPayloadSize = pxNetworkBuffer->xDataLength - sizeof( UDPPacket_t );

if( uxPayloadSize >= sizeof( DNSMessage_t ) )
{
pxDNSMessageHeader =
( DNSMessage_t * ) ( pxNetworkBuffer->pucEthernetBuffer + sizeof( UDPPacket_t ) );

/* The parameter pdFALSE indicates that the reply was not expected. */
prvParseDNSReply( ( uint8_t * ) pxDNSMessageHeader,
uxPayloadSize,
pdFALSE );
}
size_t uxPayloadSize;

/* Only proceed if the payload length indicated in the header
appears to be valid. */
if( pxNetworkBuffer->xDataLength >= sizeof( UDPPacket_t ) )
{
uxPayloadSize = pxNetworkBuffer->xDataLength - sizeof( UDPPacket_t );

if( uxPayloadSize >= sizeof( DNSMessage_t ) )
{
pxDNSMessageHeader =
( DNSMessage_t * ) ( pxNetworkBuffer->pucEthernetBuffer + sizeof( UDPPacket_t ) );

/* The parameter pdFALSE indicates that the reply was not expected. */
prvParseDNSReply( ( uint8_t * ) pxDNSMessageHeader,
uxPayloadSize,
pdFALSE );
}
}

/* The packet was not consumed. */
return pdFAIL;
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Call me crazy, but why have a return value if it can never be anything other than pdFAIL?

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Even though this handler never consumes the buffer, the IP stack expects handling code to return a status value indicating whether or not the buffer was consumed.

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