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mDNS: when a reply do not repeat the questions, set authoritative flag #1292

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0db698c
mDNS: when a reply do not repeat the questions, set authoritative flag
htibosch Sep 28, 2025
726d6a5
Repaired FreeRTOS_DNS_Parser_utest.c
htibosch Oct 15, 2025
ca67028
Formatted FreeRTOS_DNS_Globals.h
htibosch Oct 15, 2025
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96 changes: 70 additions & 26 deletions source/FreeRTOS_DNS_Parser.c
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Original file line number Diff line number Diff line change
Expand Up @@ -263,6 +263,7 @@
BaseType_t xReturn = pdTRUE;
uint32_t ulIPAddress = 0U;
BaseType_t xDNSHookReturn = 0U;
NetworkBufferDescriptor_t * pxNewBuffer = NULL;

( void ) memset( &( xSet ), 0, sizeof( xSet ) );
xSet.usPortNumber = usPort;
Expand Down Expand Up @@ -383,6 +384,13 @@
xSet.pucByte = &( xSet.pucByte[ uxResult ] );
xSet.uxSourceBytesRemaining -= uxResult;

if( ( x == 0U ) && ( xSet.usPortNumber == ipMDNS_PORT ) )
{
/* Note that the Questions section turns into the Answers section.
* uxSkipCount points to the first byte after e.g. 'name.local' */
xSet.uxSkipCount = ( size_t ) ( xSet.pucByte - pucUDPPayloadBuffer );
}

/* Check the remaining buffer size. */
if( xSet.uxSourceBytesRemaining >= sizeof( uint32_t ) )
{
Expand Down Expand Up @@ -430,6 +438,21 @@
NetworkEndPoint_t * pxEndPoint, xEndPoint;
size_t uxUDPOffset;

#if ( ipconfigUSE_IPv6 == 0 )
/* Don't treat AAAA request when IPv6 is not enabled. */
if( xSet.usType == dnsTYPE_AAAA_HOST )
{
break;
}
#endif
#if ( ipconfigUSE_IPv4 == 0 )
/* Don't treat A request when IPv4 is not enabled. */
if( xSet.usType == dnsTYPE_A_HOST )
{
break;
}
#endif

pxNetworkBuffer = pxUDPPayloadBuffer_to_NetworkBuffer( pucUDPPayloadBuffer );

/* This test could be replaced with a assert(). */
Expand Down Expand Up @@ -458,7 +481,7 @@
#if ( ipconfigUSE_IPv6 != 0 )
{
/*logging*/
FreeRTOS_printf( ( "prvParseDNS_HandleLLMNRRequest[%s]: type %04X\n", xSet.pcName, xSet.usType ) );
FreeRTOS_printf( ( "DNS_ParseDNSReply[%s]: type %04X\n", xSet.pcName, xSet.usType ) );

xEndPoint.usDNSType = ( uint8_t ) xSet.usType;
}
Expand All @@ -482,24 +505,26 @@
if( xDNSHookReturn != pdFALSE )
{
int16_t usLength;
NetworkBufferDescriptor_t * pxNewBuffer = NULL;
LLMNRAnswer_t * pxAnswer;
uint8_t * pucNewBuffer = NULL;
size_t uxExtraLength;
size_t uxDataLength = uxBufferLength +
sizeof( UDPHeader_t ) +
sizeof( EthernetHeader_t ) +
uxIPHeaderSizePacket( pxNetworkBuffer );
/* Number of bytes to write the Answers section: 16 (A) or 28 (AAAA). */
size_t uxExtraLength = 0U;
size_t uxDataLength = uxBufferLength + /* Length of the UDP payload buffer */
sizeof( UDPHeader_t ) + /* Length of the UDP header */
sizeof( EthernetHeader_t ) + /* Length of the Ethernet header */
uxIPHeaderSizePacket( pxNetworkBuffer ); /* Lentgh of IP 20 or 40. */

#if ( ipconfigUSE_IPv6 != 0 )
if( xSet.usType == dnsTYPE_AAAA_HOST )
{
/* The number of bytes needed by Answers section (28 bytes). */
uxExtraLength = sizeof( LLMNRAnswer_t ) + ipSIZE_OF_IPv6_ADDRESS - sizeof( pxAnswer->ulIPAddress );
}
else
#endif /* ( ipconfigUSE_IPv6 != 0 ) */
#if ( ipconfigUSE_IPv4 != 0 )
{
/* The number of bytes needed by Answers section (16 bytes). */
uxExtraLength = sizeof( LLMNRAnswer_t );
}
#else /* ( ipconfigUSE_IPv4 != 0 ) */
Expand All @@ -510,7 +535,8 @@

if( xBufferAllocFixedSize == pdFALSE )
{
/* Set the size of the outgoing packet. */
/* Set the size of the outgoing packet.
* setting 'xDataLength' determines the minimum number of bytes copied. */
pxNetworkBuffer->xDataLength = uxDataLength;
pxNewBuffer = pxDuplicateNetworkBufferWithDescriptor( pxNetworkBuffer,
uxDataLength +
Expand Down Expand Up @@ -553,50 +579,63 @@

if( ( pxNetworkBuffer != NULL ) )
{
pxAnswer = ( ( LLMNRAnswer_t * ) xSet.pucByte );
size_t uxDistance;

/* We leave 'usIdentifier' and 'usQuestions' untouched */
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usFlags, dnsLLMNR_FLAGS_IS_RESPONSE ); /* Set the response flag */
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usAnswers, 1 ); /* Provide a single answer */
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usAuthorityRRs, 0 ); /* No authority */
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usAdditionalRRs, 0 ); /* No additional info */
if( xSet.uxSkipCount >= 2 )
{
/* Four bytes back to write usType/usClass. */
pxAnswer = ( LLMNRAnswer_t * ) ( &( pucNewBuffer[ xSet.uxSkipCount - 2 ] ) );
/* Follow RFC6762 to set QR bit (section 18.2) and authoritative answer (AA) bit (section 18.4). */
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usFlags, dnsMDNS_FLAGS_IS_RESPONSE );
/* When replying to an mDNS request, do not include the Questions section. */
xSet.usQuestions = 0;
}
else
{
pxAnswer = ( ( LLMNRAnswer_t * ) xSet.pucByte );
/* Follow RFC4795 to set QR bit (section 2.1.1) */
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usFlags, dnsLLMNR_FLAGS_IS_RESPONSE );
}

pxAnswer->ucNameCode = dnsNAME_IS_OFFSET;
pxAnswer->ucNameOffset = ( uint8_t ) ( xSet.pcRequestedName - ( char * ) pucNewBuffer );
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usQuestions, xSet.usQuestions ); /* Might be zero. */
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usAnswers, 1 ); /* Provide a single answer */
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usAuthorityRRs, 0 ); /* No authority */
vSetField16( xSet.pxDNSMessageHeader, DNSMessage_t, usAdditionalRRs, 0 ); /* No additional info */

if( xSet.usQuestions > 0 )
{
pxAnswer->ucNameCode = dnsNAME_IS_OFFSET;
pxAnswer->ucNameOffset = ( uint8_t ) ( xSet.pcRequestedName - ( char * ) pucNewBuffer );
}

vSetField16( pxAnswer, LLMNRAnswer_t, usType, xSet.usType ); /* Type A or AAAA: host */
vSetField16( pxAnswer, LLMNRAnswer_t, usClass, dnsCLASS_IN ); /* 1: Class IN */
vSetField32( pxAnswer, LLMNRAnswer_t, ulTTL, dnsLLMNR_TTL_VALUE );

usLength = ( int16_t ) ( sizeof( *pxAnswer ) + ( size_t ) ( xSet.pucByte - pucNewBuffer ) );
uxDistance = ( size_t ) ( ( ( const uint8_t * ) pxAnswer ) - pucNewBuffer );

#if ( ipconfigUSE_IPv6 != 0 )
if( xSet.usType == dnsTYPE_AAAA_HOST )
{
size_t uxDistance;
vSetField16( pxAnswer, LLMNRAnswer_t, usDataLength, ipSIZE_OF_IPv6_ADDRESS );
( void ) memcpy( &( pxAnswer->ulIPAddress ), xEndPoint.ipv6_settings.xIPAddress.ucBytes, ipSIZE_OF_IPv6_ADDRESS );
uxDistance = ( size_t ) ( xSet.pucByte - pucNewBuffer );
/* An extra 12 bytes will be sent compared to an A-record. */
usLength = ( int16_t ) ( sizeof( *pxAnswer ) + uxDistance + ipSIZE_OF_IPv6_ADDRESS - sizeof( pxAnswer->ulIPAddress ) );
}
else
#endif /* ( ipconfigUSE_IPv6 != 0 ) */
{
size_t uxDistance;
vSetField16( pxAnswer, LLMNRAnswer_t, usDataLength, ( uint16_t ) sizeof( pxAnswer->ulIPAddress ) );
vSetField32( pxAnswer, LLMNRAnswer_t, ulIPAddress, FreeRTOS_ntohl( xEndPoint.ipv4_settings.ulIPAddress ) );
uxDistance = ( size_t ) ( xSet.pucByte - pucNewBuffer );
usLength = ( int16_t ) ( sizeof( *pxAnswer ) + uxDistance );
}

prepareReplyDNSMessage( pxNetworkBuffer, usLength );
/* This function will fill in the eth addresses and send the packet */
vReturnEthernetFrame( pxNetworkBuffer, pdFALSE );

if( pxNewBuffer != NULL )
{
vReleaseNetworkBufferAndDescriptor( pxNewBuffer );
}
/* This function will fill in the eth addresses and send the packet.
* xReleaseAfterSend = pdFALSE. */
vReturnEthernetFrame( pxNetworkBuffer, pdFALSE );
}
}
else
Expand All @@ -607,6 +646,11 @@
#endif /* ipconfigUSE_LLMNR == 1 */
( void ) uxBytesRead;
} while( ipFALSE_BOOL );

if( pxNewBuffer != NULL )
{
vReleaseNetworkBufferAndDescriptor( pxNewBuffer );
}
}

if( xReturn == pdFALSE )
Expand Down
13 changes: 8 additions & 5 deletions source/include/FreeRTOS_DNS_Globals.h
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Original file line number Diff line number Diff line change
Expand Up @@ -109,12 +109,14 @@
#define ipLLMNR_IP_ADDR 0xFC0000E0UL
#endif /* ipconfigBYTE_ORDER == pdFREERTOS_BIG_ENDIAN */

#define ipMDNS_TIME_TO_LIVE 255U
/* MDNS constants. */
#define ipMDNS_TIME_TO_LIVE 255U
#define dnsMDNS_FLAGS_IS_RESPONSE 0x8400U /**< MDNS flag value for response. */

#define ipLLMNR_PORT 5355U /* Standard LLMNR port. */
#define ipDNS_PORT 53U /* Standard DNS port. */
#define ipNBNS_PORT 137U /* NetBIOS Name Service. */
#define ipNBDGM_PORT 138U /* Datagram Service, not included. */
#define ipLLMNR_PORT 5355U /* Standard LLMNR port. */
#define ipDNS_PORT 53U /* Standard DNS port. */
#define ipNBNS_PORT 137U /* NetBIOS Name Service. */
#define ipNBDGM_PORT 138U /* Datagram Service, not included. */

/** @brief freertos_addrinfo is the equivalent of 'struct addrinfo'. */
struct freertos_addrinfo
Expand Down Expand Up @@ -175,6 +177,7 @@
uint16_t usAnswers; /**< The number of DNS answers that were given. */
uint8_t * pucUDPPayloadBuffer; /**< A pointer to the original UDP load buffer. */
uint8_t * pucByte; /**< A pointer that is used while parsing. */
size_t uxSkipCount; /**< Points to the byte after the complete name (mDNS only) */
size_t uxBufferLength; /**< The total number of bytes received in the UDP payload. */
size_t uxSourceBytesRemaining; /**< As pucByte is incremented, 'uxSourceBytesRemaining' will be decremented. */
uint16_t usType; /**< The type of address, recognised are dnsTYPE_A_HOST ( Ipv4 ) and
Expand Down
65 changes: 65 additions & 0 deletions test/unit-test/FreeRTOS_DNS_Parser/FreeRTOS_DNS_Parser_utest.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4025,3 +4025,68 @@ void test_prepareReplyDNSMessage_null_pointer( void )
uxIPHeaderSizePacket_IgnoreAndReturn( ipSIZE_OF_IPv4_HEADER );
catch_assert( prepareReplyDNSMessage( &pxNetworkBuffer, lNetLength ) );
}

void test_DNS_ParseDNSReply_mdns_request( void )
{
uint32_t ret;
uint8_t pucPacketBuffer[ 312 ];
size_t uxBufferLength = 250;
char dns[ 64 ];
struct freertos_addrinfo * pxAddressInfo;
uint16_t usPort = ipMDNS_PORT;
uint8_t * pucPayloadBuffer = pucPacketBuffer + sizeof( UDPPacket_t ); /* Skip 42 bytes. */

memset( dns, 'a', 64 );
memset( pucPacketBuffer, 0x00, sizeof pucPacketBuffer );
dns[ 63 ] = 0;
BaseType_t xExpected = pdFALSE;
size_t beg = sizeof( DNSMessage_t ); /* 8 x 2 = 16 bytes */
NetworkEndPoint_t xEndPoint = { 0 };

DNSMessage_t * dns_header;

NetworkBufferDescriptor_t xNetworkBuffer = { 0 };

xNetworkBuffer.pucEthernetBuffer = pucPacketBuffer;
xNetworkBuffer.pxEndPoint = &xEndPoint;
xEndPoint.ipv4_settings.ulIPAddress = 0xC0A8020B;

dns_header = ( DNSMessage_t * ) pucPayloadBuffer; /* pucPayloadBuffer without '&' */

dns_header->usQuestions = FreeRTOS_htons( 1 );
dns_header->usAnswers = FreeRTOS_htons( 2 );
dns_header->usFlags = 0; /* dnsEXPECTED_RX_FLAGS; */

/* Question-1: */
pucPayloadBuffer[ beg ] = 38; /* Length of name. */
beg++; /* Skip the length byte. */
strcpy( pucPayloadBuffer + beg, "FreeRTOSbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb" );
beg += 38 + 1 + 4; /* Skip name, nul-byte, and Type/Class. */

/* xApplicationDNSQueryHook_Multi() must be called. */
hook_return = pdTRUE;
/* it hasn't been called yet. */
hook_called = pdFALSE;

usChar2u16_ExpectAnyArgsAndReturn( 0x0001 ); /* usType */
usChar2u16_ExpectAnyArgsAndReturn( 0x0001 ); /* usClass */
pxUDPPayloadBuffer_to_NetworkBuffer_ExpectAnyArgsAndReturn( &xNetworkBuffer );
uxIPHeaderSizePacket_IgnoreAndReturn( ipSIZE_OF_IPv4_HEADER );

pxDuplicateNetworkBufferWithDescriptor_ExpectAnyArgsAndReturn( &xNetworkBuffer );

usGenerateChecksum_ExpectAnyArgsAndReturn( 555 );
usGenerateProtocolChecksum_ExpectAnyArgsAndReturn( 444 );

vReturnEthernetFrame_Expect( &xNetworkBuffer, pdFALSE );
vReleaseNetworkBufferAndDescriptor_Expect( &xNetworkBuffer );

ret = DNS_ParseDNSReply( pucPayloadBuffer,
beg, /* uxBufferLength, */
&pxAddressInfo,
xExpected,
usPort );

TEST_ASSERT_EQUAL( pdFALSE, ret );
ASSERT_DNS_QUERY_HOOK_CALLED();
}
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