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fix(010): never enable UDP_GRO on android (GRO split-brain killed download)

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runtime.GOOS=="android" (not "linux"), so StdNetBind enabled UDP_GRO and read
rxOffload=true, but the GRO receive dispatcher in bind_std.go is gated on
GOOS=="linux" → dead on android. A coalesced GRO super-packet was read as one
datagram, corrupting the WG transport stream → download died on no-detour
WG-endpoint (detour path uses ClientBind, no offload, so it worked).

Gate both the UDP_GRO setsockopt (controlfns_linux.go) and the rxOffload
readback (features_linux.go) behind !android. TX/GSO untouched, so non-android
linux performance is unchanged. Confirmed on device (CPH2411/Android-15:
probe gave rxOffload=true + dispatch=single).

See SPECS/010-B-O-WG_ENDPOINT_GRO_SPLIT_BRAIN.
This commit is contained in:
Leadaxe 2026-06-21 15:49:57 +03:00
parent 7b15aacbfe
commit fb8d8d8fca
2 changed files with 19 additions and 0 deletions
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9
conn/controlfns_linux.go
View file

@ -60,6 +60,15 @@ func init() {
// Attempt to enable UDP_GRO // Attempt to enable UDP_GRO
func(network, address string, c syscall.RawConn) error { func(network, address string, c syscall.RawConn) error {
// lx(010): skip UDP_GRO on android. The GRO receive path in bind_std.go
// is gated on runtime.GOOS=="linux", which is false on android — so a
// coalesced super-packet is never split and corrupts the WG stream
// (download dies). Belt-and-suspenders with the rxOffload guard in
// features_linux.go. TX/GSO untouched.
// See SPECS/010-B-O-WG_ENDPOINT_GRO_SPLIT_BRAIN.
if runtime.GOOS == "android" {
return nil
}
c.Control(func(fd uintptr) { c.Control(func(fd uintptr) {
_ = unix.SetsockoptInt(int(fd), unix.IPPROTO_UDP, socketOptionUDPGRO, 1) _ = unix.SetsockoptInt(int(fd), unix.IPPROTO_UDP, socketOptionUDPGRO, 1)
}) })

10
conn/features_linux.go
View file

@ -7,6 +7,7 @@ package conn
import ( import (
"net" "net"
"runtime"
"golang.org/x/sys/unix" "golang.org/x/sys/unix"
) )
@ -29,6 +30,15 @@ func supportsUDPOffload(conn *net.UDPConn) (txOffload, rxOffload bool) {
return return
} }
txOffload = true txOffload = true
// lx(010): never advertise RX offload on android. runtime.GOOS=="android"
// (not "linux"), so the GRO receive dispatcher in bind_std.go (gated on
// GOOS=="linux") is dead there — a coalesced GRO super-packet would be read
// as one datagram and corrupt the WG transport stream, killing download.
// Confirmed on device (CPH2411/Android-15: rxOffload=true, dispatch=single).
// TX is left untouched. See SPECS/010-B-O-WG_ENDPOINT_GRO_SPLIT_BRAIN.
if runtime.GOOS == "android" {
return
}
opt, errSyscall := unix.GetsockoptInt(int(fd), unix.IPPROTO_UDP, socketOptionUDPGRO) opt, errSyscall := unix.GetsockoptInt(int(fd), unix.IPPROTO_UDP, socketOptionUDPGRO)
if errSyscall != nil { if errSyscall != nil {
return return