[vfs2] Implement /proc/sys/net/ipv4/tcp_rmem and /proc/sys/net/ipv4/tcp_wmem.

Updates #1035

PiperOrigin-RevId: 327253907

2 files changed, 106 insertions, 5 deletions

diff --git a/pkg/sentry/fsimpl/proc/BUILD b/pkg/sentry/fsimpl/proc/BUILD
index 6014138ff..14ecfd300 100644
--- a/pkg/sentry/fsimpl/proc/BUILD
+++ b/pkg/sentry/fsimpl/proc/BUILD
@@ -36,6 +36,7 @@ go_library(
         "//pkg/sentry/socket/unix/transport",
         "//pkg/sentry/usage",
         "//pkg/sentry/vfs",
+        "//pkg/sync",
         "//pkg/syserror",
         "//pkg/tcpip/header",
         "//pkg/usermem",
diff --git a/pkg/sentry/fsimpl/proc/tasks_sys.go b/pkg/sentry/fsimpl/proc/tasks_sys.go
index b71778128..6435385ef 100644
--- a/pkg/sentry/fsimpl/proc/tasks_sys.go
+++ b/pkg/sentry/fsimpl/proc/tasks_sys.go
@@ -25,10 +25,18 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/usermem"
 )
 
+type tcpMemDir int
+
+const (
+	tcpRMem tcpMemDir = iota
+	tcpWMem
+)
+
 // newSysDir returns the dentry corresponding to /proc/sys directory.
 func (fs *filesystem) newSysDir(root *auth.Credentials, k *kernel.Kernel) *kernfs.Dentry {
 	return kernfs.NewStaticDir(root, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), 0555, map[string]*kernfs.Dentry{
@@ -56,7 +64,9 @@ func (fs *filesystem) newSysNetDir(root *auth.Credentials, k *kernel.Kernel) *ke
 		contents = map[string]*kernfs.Dentry{
 			"ipv4": kernfs.NewStaticDir(root, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), 0555, map[string]*kernfs.Dentry{
 				"tcp_recovery": fs.newDentry(root, fs.NextIno(), 0644, &tcpRecoveryData{stack: stack}),
+				"tcp_rmem":     fs.newDentry(root, fs.NextIno(), 0644, &tcpMemData{stack: stack, dir: tcpRMem}),
 				"tcp_sack":     fs.newDentry(root, fs.NextIno(), 0644, &tcpSackData{stack: stack}),
+				"tcp_wmem":     fs.newDentry(root, fs.NextIno(), 0644, &tcpMemData{stack: stack, dir: tcpWMem}),
 
 				// The following files are simple stubs until they are implemented in
 				// netstack, most of these files are configuration related. We use the
@@ -181,10 +191,11 @@ func (d *tcpSackData) Generate(ctx context.Context, buf *bytes.Buffer) error {
 		// Tough luck.
 		val = "1\n"
 	}
-	buf.WriteString(val)
-	return nil
+	_, err := buf.WriteString(val)
+	return err
 }
 
+// Write implements vfs.WritableDynamicBytesSource.Write.
 func (d *tcpSackData) Write(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
 	if offset != 0 {
 		// No need to handle partial writes thus far.
@@ -200,7 +211,7 @@ func (d *tcpSackData) Write(ctx context.Context, src usermem.IOSequence, offset
 	var v int32
 	n, err := usermem.CopyInt32StringInVec(ctx, src.IO, src.Addrs, &v, src.Opts)
 	if err != nil {
-		return n, err
+		return 0, err
 	}
 	if d.enabled == nil {
 		d.enabled = new(bool)
@@ -228,10 +239,11 @@ func (d *tcpRecoveryData) Generate(ctx context.Context, buf *bytes.Buffer) error
 		return err
 	}
 
-	buf.WriteString(fmt.Sprintf("%d\n", recovery))
-	return nil
+	_, err = buf.WriteString(fmt.Sprintf("%d\n", recovery))
+	return err
 }
 
+// Write implements vfs.WritableDynamicBytesSource.Write.
 func (d *tcpRecoveryData) Write(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
 	if offset != 0 {
 		// No need to handle partial writes thus far.
@@ -254,3 +266,91 @@ func (d *tcpRecoveryData) Write(ctx context.Context, src usermem.IOSequence, off
 	}
 	return n, nil
 }
+
+// tcpMemData implements vfs.WritableDynamicBytesSource for
+// /proc/sys/net/ipv4/tcp_rmem and /proc/sys/net/ipv4/tcp_wmem.
+//
+// +stateify savable
+type tcpMemData struct {
+	kernfs.DynamicBytesFile
+
+	dir   tcpMemDir
+	stack inet.Stack `state:"wait"`
+
+	// mu protects against concurrent reads/writes to FDs based on the dentry
+	// backing this byte source.
+	mu sync.Mutex `state:"nosave"`
+}
+
+var _ vfs.WritableDynamicBytesSource = (*tcpMemData)(nil)
+
+// Generate implements vfs.DynamicBytesSource.
+func (d *tcpMemData) Generate(ctx context.Context, buf *bytes.Buffer) error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	size, err := d.readSizeLocked()
+	if err != nil {
+		return err
+	}
+	_, err = buf.WriteString(fmt.Sprintf("%d\t%d\t%d\n", size.Min, size.Default, size.Max))
+	return err
+}
+
+// Write implements vfs.WritableDynamicBytesSource.Write.
+func (d *tcpMemData) Write(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
+	if offset != 0 {
+		// No need to handle partial writes thus far.
+		return 0, syserror.EINVAL
+	}
+	if src.NumBytes() == 0 {
+		return 0, nil
+	}
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	// Limit the amount of memory allocated.
+	src = src.TakeFirst(usermem.PageSize - 1)
+	size, err := d.readSizeLocked()
+	if err != nil {
+		return 0, err
+	}
+	buf := []int32{int32(size.Min), int32(size.Default), int32(size.Max)}
+	n, err := usermem.CopyInt32StringsInVec(ctx, src.IO, src.Addrs, buf, src.Opts)
+	if err != nil {
+		return 0, err
+	}
+	newSize := inet.TCPBufferSize{
+		Min:     int(buf[0]),
+		Default: int(buf[1]),
+		Max:     int(buf[2]),
+	}
+	if err := d.writeSizeLocked(newSize); err != nil {
+		return 0, err
+	}
+	return n, nil
+}
+
+// Precondition: d.mu must be locked.
+func (d *tcpMemData) readSizeLocked() (inet.TCPBufferSize, error) {
+	switch d.dir {
+	case tcpRMem:
+		return d.stack.TCPReceiveBufferSize()
+	case tcpWMem:
+		return d.stack.TCPSendBufferSize()
+	default:
+		panic(fmt.Sprintf("unknown tcpMemFile type: %v", d.dir))
+	}
+}
+
+// Precondition: d.mu must be locked.
+func (d *tcpMemData) writeSizeLocked(size inet.TCPBufferSize) error {
+	switch d.dir {
+	case tcpRMem:
+		return d.stack.SetTCPReceiveBufferSize(size)
+	case tcpWMem:
+		return d.stack.SetTCPSendBufferSize(size)
+	default:
+		panic(fmt.Sprintf("unknown tcpMemFile type: %v", d.dir))
+	}
+}