From 1fe6db8c542431d3d6e229f563fefbd2f962fc81 Mon Sep 17 00:00:00 2001
From: Kevin Krakauer <krakauer@google.com>
Date: Tue, 13 Jul 2021 11:18:15 -0700
Subject: netstack: atomically update buffer sizes

Previously, two calls to set the send or receive buffer size could have raced
and left state wherein:
- The actual size depended on one call
- The value returned by getsockopt() depended on the other

PiperOrigin-RevId: 384508720
---
 pkg/tcpip/socketops.go | 48 +++++++++++++++++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 17 deletions(-)

diff --git a/pkg/tcpip/socketops.go b/pkg/tcpip/socketops.go
index cc735c9ce..042326a3a 100644
--- a/pkg/tcpip/socketops.go
+++ b/pkg/tcpip/socketops.go
@@ -17,7 +17,6 @@ package tcpip
 import (
 	"sync/atomic"
 
-	"gvisor.dev/gvisor/pkg/atomicbitops"
 	"gvisor.dev/gvisor/pkg/sync"
 )
 
@@ -208,16 +207,24 @@ type SocketOptions struct {
 	// will not change.
 	getSendBufferLimits GetSendBufferLimits `state:"manual"`
 
+	// sendBufSizeMu protects sendBufferSize and calls to
+	// handler.OnSetSendBufferSize.
+	sendBufSizeMu sync.Mutex `state:"nosave"`
+
 	// sendBufferSize determines the send buffer size for this socket.
-	sendBufferSize atomicbitops.AlignedAtomicInt64
+	sendBufferSize int64
 
 	// getReceiveBufferLimits provides the handler to get the min, default and
 	// max size for receive buffer. It is initialized at the creation time and
 	// will not change.
 	getReceiveBufferLimits GetReceiveBufferLimits `state:"manual"`
 
+	// receiveBufSizeMu protects receiveBufferSize and calls to
+	// handler.OnSetReceiveBufferSize.
+	receiveBufSizeMu sync.Mutex `state:"nosave"`
+
 	// receiveBufferSize determines the receive buffer size for this socket.
-	receiveBufferSize atomicbitops.AlignedAtomicInt64
+	receiveBufferSize int64
 
 	// mu protects the access to the below fields.
 	mu sync.Mutex `state:"nosave"`
@@ -607,11 +614,6 @@ func (so *SocketOptions) SetBindToDevice(bindToDevice int32) Error {
 	return nil
 }
 
-// GetSendBufferSize gets value for SO_SNDBUF option.
-func (so *SocketOptions) GetSendBufferSize() int64 {
-	return so.sendBufferSize.Load()
-}
-
 // SendBufferLimits returns the [min, max) range of allowable send buffer
 // sizes.
 func (so *SocketOptions) SendBufferLimits() (min, max int64) {
@@ -619,18 +621,22 @@ func (so *SocketOptions) SendBufferLimits() (min, max int64) {
 	return int64(limits.Min), int64(limits.Max)
 }
 
+// GetSendBufferSize gets value for SO_SNDBUF option.
+func (so *SocketOptions) GetSendBufferSize() int64 {
+	so.sendBufSizeMu.Lock()
+	defer so.sendBufSizeMu.Unlock()
+	return so.sendBufferSize
+}
+
 // SetSendBufferSize sets value for SO_SNDBUF option. notify indicates if the
 // stack handler should be invoked to set the send buffer size.
 func (so *SocketOptions) SetSendBufferSize(sendBufferSize int64, notify bool) {
+	so.sendBufSizeMu.Lock()
+	defer so.sendBufSizeMu.Unlock()
 	if notify {
 		sendBufferSize = so.handler.OnSetSendBufferSize(sendBufferSize)
 	}
-	so.sendBufferSize.Store(sendBufferSize)
-}
-
-// GetReceiveBufferSize gets value for SO_RCVBUF option.
-func (so *SocketOptions) GetReceiveBufferSize() int64 {
-	return so.receiveBufferSize.Load()
+	so.sendBufferSize = sendBufferSize
 }
 
 // ReceiveBufferLimits returns the [min, max) range of allowable receive buffer
@@ -640,12 +646,20 @@ func (so *SocketOptions) ReceiveBufferLimits() (min, max int64) {
 	return int64(limits.Min), int64(limits.Max)
 }
 
+// GetReceiveBufferSize gets value for SO_RCVBUF option.
+func (so *SocketOptions) GetReceiveBufferSize() int64 {
+	so.receiveBufSizeMu.Lock()
+	defer so.receiveBufSizeMu.Unlock()
+	return so.receiveBufferSize
+}
+
 // SetReceiveBufferSize sets the value of the SO_RCVBUF option, optionally
 // notifying the owning endpoint.
 func (so *SocketOptions) SetReceiveBufferSize(receiveBufferSize int64, notify bool) {
+	so.receiveBufSizeMu.Lock()
+	defer so.receiveBufSizeMu.Unlock()
 	if notify {
-		oldSz := so.receiveBufferSize.Load()
-		receiveBufferSize = so.handler.OnSetReceiveBufferSize(receiveBufferSize, oldSz)
+		receiveBufferSize = so.handler.OnSetReceiveBufferSize(receiveBufferSize, so.receiveBufferSize)
 	}
-	so.receiveBufferSize.Store(receiveBufferSize)
+	so.receiveBufferSize = receiveBufferSize
 }
-- 
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