Merge pull request #2313 from kevinGC:firstn

PiperOrigin-RevId: 307477185

2 files changed, 6 insertions, 4 deletions

diff --git a/pkg/sentry/socket/netfilter/tcp_matcher.go b/pkg/sentry/socket/netfilter/tcp_matcher.go
index ff1cfd8f6..55c0f04f3 100644
--- a/pkg/sentry/socket/netfilter/tcp_matcher.go
+++ b/pkg/sentry/socket/netfilter/tcp_matcher.go
@@ -121,12 +121,13 @@ func (tm *TCPMatcher) Match(hook stack.Hook, pkt stack.PacketBuffer, interfaceNa
 		tcpHeader = header.TCP(pkt.TransportHeader)
 	} else {
 		// The TCP header hasn't been parsed yet. We have to do it here.
-		if len(pkt.Data.First()) < header.TCPMinimumSize {
+		hdr, ok := pkt.Data.PullUp(header.TCPMinimumSize)
+		if !ok {
 			// There's no valid TCP header here, so we hotdrop the
 			// packet.
 			return false, true
 		}
-		tcpHeader = header.TCP(pkt.Data.First())
+		tcpHeader = header.TCP(hdr)
 	}
 
 	// Check whether the source and destination ports are within the
diff --git a/pkg/sentry/socket/netfilter/udp_matcher.go b/pkg/sentry/socket/netfilter/udp_matcher.go
index 3359418c1..04d03d494 100644
--- a/pkg/sentry/socket/netfilter/udp_matcher.go
+++ b/pkg/sentry/socket/netfilter/udp_matcher.go
@@ -120,12 +120,13 @@ func (um *UDPMatcher) Match(hook stack.Hook, pkt stack.PacketBuffer, interfaceNa
 		udpHeader = header.UDP(pkt.TransportHeader)
 	} else {
 		// The UDP header hasn't been parsed yet. We have to do it here.
-		if len(pkt.Data.First()) < header.UDPMinimumSize {
+		hdr, ok := pkt.Data.PullUp(header.UDPMinimumSize)
+		if !ok {
 			// There's no valid UDP header here, so we hotdrop the
 			// packet.
 			return false, true
 		}
-		udpHeader = header.UDP(pkt.Data.First())
+		udpHeader = header.UDP(hdr)
 	}
 
 	// Check whether the source and destination ports are within the