From b6461c01f367285577787b78655c064ad548959b Mon Sep 17 00:00:00 2001
From: Andrei Vagin <avagin@google.com>
Date: Fri, 10 May 2024 15:20:23 -0700
Subject: [PATCH] upd: don't read any data from payloader if a send buffer is
 full

The caller will wait for the endpointto become writable and try again.

Fixes #8566

Signed-off-by: Andrei Vagin <avagin@google.com>
---
 .../transport/internal/network/endpoint.go    | 27 +++++++++++++++++++
 pkg/tcpip/transport/udp/endpoint.go           | 14 ++--------
 2 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/pkg/tcpip/transport/internal/network/endpoint.go b/pkg/tcpip/transport/internal/network/endpoint.go
index 9d61e881e8..960d7d862a 100644
--- a/pkg/tcpip/transport/internal/network/endpoint.go
+++ b/pkg/tcpip/transport/internal/network/endpoint.go
@@ -274,7 +274,34 @@ func (c *WriteContext) TryNewPacketBuffer(reserveHdrBytes int, data buffer.Buffe
 	if !e.hasSendSpaceRLocked() {
 		return nil
 	}
+	return c.newPacketBufferLocked(reserveHdrBytes, data)
+}
+
+// TryNewPacketBufferFromPayloader returns a new packet buffer iff the endpoint's send buffer
+// is not full. Otherwise, data from `payloader` isn't read.
+//
+// If this method returns nil, the caller should wait for the endpoint to become
+// writable.
+func (c *WriteContext) TryNewPacketBufferFromPayloader(reserveHdrBytes int, payloader tcpip.Payloader) *stack.PacketBuffer {
+	e := c.e
+
+	e.sendBufferSizeInUseMu.Lock()
+	defer e.sendBufferSizeInUseMu.Unlock()
 
+	if !e.hasSendSpaceRLocked() {
+		return nil
+	}
+	var data buffer.Buffer
+	if _, err := data.WriteFromReader(payloader, int64(payloader.Len())); err != nil {
+		data.Release()
+		return nil
+	}
+	return c.newPacketBufferLocked(reserveHdrBytes, data)
+}
+
+// +checklocks:c.e.sendBufferSizeInUseMu
+func (c *WriteContext) newPacketBufferLocked(reserveHdrBytes int, data buffer.Buffer) *stack.PacketBuffer {
+	e := c.e
 	// Note that we allow oversubscription - if there is any space at all in the
 	// send buffer, we accept the full packet which may be larger than the space
 	// available. This is because if the endpoint reports that it is writable,
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 0c21be861d..6c4de0a103 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -21,7 +21,6 @@ import (
 	"math"
 	"time"
 
-	"gvisor.dev/gvisor/pkg/buffer"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/checksum"
@@ -436,16 +435,8 @@ func (e *endpoint) prepareForWrite(p tcpip.Payloader, opts tcpip.WriteOptions) (
 		return udpPacketInfo{}, &tcpip.ErrMessageTooLong{}
 	}
 
-	var buf buffer.Buffer
-	if _, err := buf.WriteFromReader(p, int64(p.Len())); err != nil {
-		buf.Release()
-		ctx.Release()
-		return udpPacketInfo{}, &tcpip.ErrBadBuffer{}
-	}
-
 	return udpPacketInfo{
 		ctx:        ctx,
-		data:       buf,
 		localPort:  e.localPort,
 		remotePort: dst.Port,
 	}, nil
@@ -473,9 +464,9 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, tcp
 	}
 	defer udpInfo.ctx.Release()
 
-	dataSz := udpInfo.data.Size()
+	dataSz := p.Len()
 	pktInfo := udpInfo.ctx.PacketInfo()
-	pkt := udpInfo.ctx.TryNewPacketBuffer(header.UDPMinimumSize+int(pktInfo.MaxHeaderLength), udpInfo.data)
+	pkt := udpInfo.ctx.TryNewPacketBufferFromPayloader(header.UDPMinimumSize+int(pktInfo.MaxHeaderLength), p)
 	if pkt == nil {
 		return 0, &tcpip.ErrWouldBlock{}
 	}
@@ -593,7 +584,6 @@ func (e *endpoint) GetSockOpt(opt tcpip.GettableSocketOption) tcpip.Error {
 // udpPacketInfo holds information needed to send a UDP packet.
 type udpPacketInfo struct {
 	ctx        network.WriteContext
-	data       buffer.Buffer
 	localPort  uint16
 	remotePort uint16
 }