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internal: reject inbound packets that are not block aligned #1189

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internal: reject inbound packets that are not block aligned #1189

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17 changes: 17 additions & 0 deletions src/internal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -12813,10 +12813,12 @@ int DoReceive(WOLFSSH* ssh)
int ret = WS_SUCCESS;
int verifyResult;
word32 readSz;
word32 alignSz;
byte peerBlockSz = ssh->peerBlockSz;
byte peerMacSz = ssh->peerMacSz;
byte aeadMode = ssh->peerAeadMode;
byte bufferConsumed = 0;
byte alignBlockSz;

switch (ssh->processReplyState) {
case PROCESS_INIT:
Expand Down Expand Up @@ -12855,6 +12857,21 @@ int DoReceive(WOLFSSH* ssh)
ssh->error = WS_OVERFLOW_E;
return WS_FATAL_ERROR;
}

/* RFC 4253 section 6 aligns packet_length through the padding
* on the block size, or 8, whichever is larger. Under AES-GCM
* the length is AAD, so RFC 5647 section 7.2 aligns the body. */
alignBlockSz = peerBlockSz < MIN_BLOCK_SZ ?
MIN_BLOCK_SZ : peerBlockSz;
alignSz = aeadMode ? ssh->curSz : UINT32_SZ + ssh->curSz;
if (alignSz % alignBlockSz != 0) {
WLOG(WS_LOG_DEBUG,
"Packet not block aligned: aligned size = %u, "
"block = %u, aead = %u",
alignSz, (word32)alignBlockSz, (word32)aeadMode);
ssh->error = WS_BUFFER_E;
return WS_FATAL_ERROR;
}
ssh->processReplyState = PROCESS_PACKET_FINISH;
FALL_THROUGH;

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5 changes: 2 additions & 3 deletions tests/regress.c
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Original file line number Diff line number Diff line change
Expand Up @@ -107,11 +107,10 @@ static HandshakeInfo* AllocHandshake(WOLFSSH* ssh)
}

/* Build a minimal SSH binary packet carrying only a message ID.
* Layout: uint32 packetLen, byte padLen, payload[msgId], pad[padLen].
* Choose padLen so total is 8-byte aligned for the clear transport case. */
* Layout: uint32 packetLen, byte padLen, payload[msgId], pad[padLen]. */
static word32 BuildPacket(byte msgId, byte* out, word32 outSz)
{
byte padLen = 6; /* 1 (msgId) +1 (padLen) +6 = 8 */
byte padLen = 10; /* 4 (len) +1 (padLen) +1 (msgId) +10 = 16 */
word32 packetLen = 1 + 1 + padLen; /* payload + padLen field + pad */
word32 need = 4 + packetLen;

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