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nft: never TPROXY a client DNS query redirected to the router #6

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Merged
Asofwar merged 1 commit into from
Oct 17, 2026
Merged

nft: never TPROXY a client DNS query redirected to the router #6

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8 changes: 8 additions & 0 deletions prokop/files/usr/lib/nft/apply.uc
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Original file line number Diff line number Diff line change
Expand Up @@ -1561,6 +1561,14 @@ function nft_create_runtime_base(table, localv4_set, common_set, port_set, ip_po
!nft_add_rule(table, "mangle", [ "iifname", "@" + as_string(interface_set), "ip", "daddr", fakeip_range, "meta", "l4proto", "udp", "meta", "mark", "set", fakeip_mark, "counter" ]) ||
!nft_add_rule(table, "mangle", [ "iifname", "@" + as_string(interface_set), "ip6", "daddr", fakeip6_range, "meta", "l4proto", "tcp", "meta", "mark", "set", fakeip_mark, "counter" ]) ||
!nft_add_rule(table, "mangle", [ "iifname", "@" + as_string(interface_set), "ip6", "daddr", fakeip6_range, "meta", "l4proto", "udp", "meta", "mark", "set", fakeip_mark, "counter" ]) ||
// mangle (-149) marks the first packet of a flow before dns_redirect
// (-101) rewrites it, so a client query to a captured resolver such
// as 8.8.8.8 arrives here redirected to the router's own :53 or
// :1603 and still marked. TPROXY of that packet makes sing-box answer
// from a transparent socket bound to that local address, which then
// takes the LAN's queries meant for dnsmasq and never reads them.
// A redirected packet is already delivered locally: never TPROXY it.
!nft_add_rule(table, "proxy", [ "ct", "status", "dnat", "return" ]) ||
!nft_add_rule(table, "proxy", [ "meta", "mark", "&", fakeip_mark, "==", fakeip_mark, "meta", "l4proto", "tcp", "tproxy", "ip", "to", ":" + as_string(tproxy_port), "counter" ]) ||
!nft_add_rule(table, "proxy", [ "meta", "mark", "&", fakeip_mark, "==", fakeip_mark, "meta", "l4proto", "udp", "tproxy", "ip", "to", ":" + as_string(tproxy_port), "counter" ]) ||
!nft_add_rule(table, "proxy", [ "meta", "mark", "&", fakeip_mark, "==", fakeip_mark, "meta", "l4proto", "tcp", "tproxy", "ip6", "to", core_ip.format_ipv6_tproxy_target(tproxy6_address, tproxy_port), "counter" ]) ||
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5 changes: 5 additions & 0 deletions tests/nft_apply.sh
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Expand Up @@ -231,6 +231,11 @@ for shared_set in prokop_subnets prokop_subnets6 prokop_ports prokop_ip_ports pr
done
assert_contains "$NFT_LOG" $'nft\tadd\trule\tinet\tProkopTable\tproxy\tmeta\tmark\t&\t0x00100000\t==\t0x00100000\tmeta\tl4proto\ttcp\ttproxy\tip\tto\t:1602\tcounter' "runtime proxy tcp rule"
assert_contains "$NFT_LOG" $'nft\tadd\trule\tinet\tProkopTable\tproxy\tmeta\tmark\t&\t0x00100000\t==\t0x00100000\tmeta\tl4proto\ttcp\ttproxy\tip6\tto\t[::1]:1602\tcounter' "runtime proxy6 tcp rule"
# mangle marks a client query to a captured resolver (8.8.8.8) before
# dns_redirect sends it to the router's :53; TPROXY of that redirected packet
# left sing-box sockets on 192.168.1.1:53 that swallowed the LAN's DNS.
[ "$(grep -F $'\tProkopTable\tproxy\t' "$NFT_LOG" | grep -F $'\trule\t' | head -n 1 | cut -f7- | tr '\t' ' ')" = 'ct status dnat return' ] ||
fail "proxy must skip redirected (DNAT) packets before any TPROXY rule"
assert_contains "$NFT_LOG" $'nft\tadd\trule\tinet\tProkopTable\tmangle_output\tmeta\tmark\t&\t0xff2000ff\t==\t0x00200000\tcounter\treturn' "runtime outbound return on Prokop's mark bits"
assert_contains "$NFT_LOG" $'nft\tadd\trule\tinet\tProkopTable\tmangle_output\tip6\tdaddr\t@localv6\tip6\tdaddr\t!=\tfc00::/18\treturn' "runtime output local6 return preserves FakeIP6 capture"
assert_contains "$NFT_LOG" $'nft\tadd\trule\tinet\tProkopTable\tmangle_output\tjump\tpriority_output_rules' "runtime priority output jump"
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