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Correctly estimate the initial MTU for legacy packets.

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This commit is contained in:
Guus Sliepen 2015-01-10 23:00:51 +01:00
parent 0e65326047
commit 0209f12d27
3 changed files with 27 additions and 0 deletions
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19
src/net_packet.c
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@ -929,6 +929,25 @@ static length_t choose_initial_maxmtu(node_t *n) {
mtu -= SPTPS_DATAGRAM_OVERHEAD;
if((n->options >> 24) >= 4)
mtu -= sizeof(node_id_t) + sizeof(node_id_t);
} else {
mtu -= digest_length(n->outdigest);
/* Now it's tricky. We use CBC mode, so the length of the
encrypted payload must be a multiple of the blocksize. The
sequence number is also part of the encrypted payload, so we
must account for it after correcting for the blocksize.
Furthermore, the padding in the last block must be at least
1 byte. */
length_t blocksize = cipher_blocksize(n->outcipher);
if(blocksize > 1) {
mtu /= blocksize;
mtu *= blocksize;
mtu--;
}
mtu -= 4; // seqno
}
if (mtu < 512) {