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engine: randomize outgoing_sequence on server side

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This commit is contained in:
Alibek Omarov
2026-05-25 21:42:39 +05:00
committed by a1batross
parent c3f4eb026b
commit d61983a5d2
1 changed files with 13 additions and 2 deletions
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15
engine/common/net_chan.c
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@@ -241,7 +241,16 @@ void Netchan_Setup( netsrc_t sock, netchan_t *chan, netadr_t adr, int qport, voi
chan->last_received = host.realtime;
chan->connect_time = host.realtime;
chan->incoming_sequence = 0;
chan->outgoing_sequence = 1;
// the server picks a random initial outgoing sequence so a remote attacker can't guess where in the sequence space the channel is
// kept well below BIT( 30 ) — bits 30/31 are reserved for the flags
// FIXME: BIT( 27 ) taken so in the worst case we have few months of stable client<->server connection
// as netchan doesn't currently handle wrapping around
if( sock == NS_SERVER )
chan->outgoing_sequence = COM_RandomLong( 1, BIT( 27 ) - 1 );
else
chan->outgoing_sequence = 1;
chan->rate = DEFAULT_RATE;
chan->qport = qport;
chan->client = client;
@@ -1859,7 +1868,9 @@ qboolean Netchan_Process( netchan_t *chan, sizebuf_t *msg )
}
// reject packets that leap too far ahead of the expected sequence
if( net_sequence_window.value > 0 && sequence > chan->incoming_sequence + (uint)net_sequence_window.value )
// skip on the very first packet — the server starts with a random
// outgoing_sequence, so the first one legitimately jumps far ahead of 0
if( chan->incoming_sequence != 0 && net_sequence_window.value > 0 && sequence > chan->incoming_sequence + (uint)net_sequence_window.value )
{
Con_Printf( S_WARN "%s: %s: sequence %u jumps %u ahead of expected %i (window %i), dropping\n",
__func__, NET_AdrToString( chan->remote_address ),