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pkg/snet: ignore decoding/parsing reading errors on SCIONPacketConn #4670

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merged 2 commits into from
Dec 23, 2024
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pkg/snet: ignore decoding/parsing reading errors on SCIONPacketConn #4670

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7ef97ef
ignore decoding/parsing errors in ReadFrom on SCIONPacketConn
JordiSubira Dec 19, 2024
9858816
pass
JordiSubira Dec 19, 2024
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33 changes: 31 additions & 2 deletions pkg/snet/packet_conn.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ import (
"time"

"github.com/scionproto/scion/pkg/addr"
"github.com/scionproto/scion/pkg/log"
"github.com/scionproto/scion/pkg/metrics/v2"
"github.com/scionproto/scion/pkg/private/common"
"github.com/scionproto/scion/pkg/private/serrors"
Expand Down Expand Up @@ -168,6 +169,14 @@ func (c *SCIONPacketConn) ReadFrom(pkt *Packet, ov *net.UDPAddr) error {
if err != nil {
return err
}
if remoteAddr == nil {
// XXX(JordiSubira): The remote address of the underlay next host
// will not be nil unless there was an error while reading the
// SCION packet. If the err is nil, it means that it was a
// non-recoverable error (e.g., decoding the header) and we
// discard the packet and keep reading.
continue
}
*ov = *remoteAddr
if scmp, ok := pkt.Payload.(SCMPPayload); ok {
if c.SCMPHandler == nil {
Expand Down Expand Up @@ -206,7 +215,17 @@ func (c *SCIONPacketConn) readFrom(pkt *Packet) (*net.UDPAddr, error) {
pkt.Bytes = pkt.Bytes[:n]
if err := pkt.Decode(); err != nil {
metrics.CounterInc(c.Metrics.ParseErrors)
return nil, serrors.Wrap("decoding packet", err)
// XXX(JordiSubira): We avoid bubbling up parsing errors to the
// caller application. This simulates that the network stack
// simply discards incorrect/malformated packets. Otherwise,
// some libraries/applications would misbehave (similar to what
// would happen if were to receive SCMP errors).
//
// If we believe that SCION-aware applications using the low-level
// SCIONPacketConn should receive the error, we can move this up to
// Conn.
log.Error("decoding packet", "error", err)
return nil, nil
}

udpRemoteAddr := remoteAddr.(*net.UDPAddr)
Expand All @@ -218,7 +237,17 @@ func (c *SCIONPacketConn) readFrom(pkt *Packet) (*net.UDPAddr, error) {
// *loopback:30041* `SCIONPacketConn.lastHop()` should yield the right next hop address.
lastHop, err = c.lastHop(pkt)
if err != nil {
return nil, serrors.Wrap("extracting last hop based on packet path", err)
// XXX(JordiSubira): We avoid bubbling up parsing errors to the
// caller application. This simulates that the network stack
// simply discards incorrect/malformated packets. Otherwise,
// some libraries/applications would misbehave (similar to what
// would happen if were to receive SCMP errors).
//
// If we believe that SCION-aware applications using the low-level
// SCIONPacketConn should receive the error, we can move this up to
// Conn.
log.Error("extracting last hop based on packet path", "error", err)
return nil, nil
}
}
return lastHop, nil
Expand Down
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