Support pipes and sockets in VFS2 gofer fs.

Named pipes and sockets can be represented in two ways in gofer fs:
1. As a file on the remote filesystem. In this case, all file operations are
   passed through 9p.
2. As a synthetic file that is internal to the sandbox. In this case, the
   dentry stores an endpoint or VFSPipe for sockets and pipes respectively,
   which replaces interactions with the remote fs through the gofer.
In gofer.filesystem.MknodAt, we attempt to call mknod(2) through 9p,
and if it fails, fall back to the synthetic version.

Updates #1200.

PiperOrigin-RevId: 308828161

1 files changed, 27 insertions, 5 deletions

diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index 8b4e91d17..3235816c2 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -46,9 +46,11 @@ import (
 	"gvisor.dev/gvisor/pkg/p9"
 	"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/pipe"
 	ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
 	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/unet"
@@ -585,6 +587,14 @@ type dentry struct {
 	// and target are protected by dataMu.
 	haveTarget bool
 	target     string
+
+	// If this dentry represents a synthetic socket file, endpoint is the
+	// transport endpoint bound to this file.
+	endpoint transport.BoundEndpoint
+
+	// If this dentry represents a synthetic named pipe, pipe is the pipe
+	// endpoint bound to this file.
+	pipe *pipe.VFSPipe
 }
 
 // dentryAttrMask returns a p9.AttrMask enabling all attributes used by the
@@ -791,10 +801,21 @@ func (d *dentry) setStat(ctx context.Context, creds *auth.Credentials, stat *lin
 		setLocalAtime = stat.Mask&linux.STATX_ATIME != 0
 		setLocalMtime = stat.Mask&linux.STATX_MTIME != 0
 		stat.Mask &^= linux.STATX_ATIME | linux.STATX_MTIME
-		if !setLocalMtime && (stat.Mask&linux.STATX_SIZE != 0) {
-			// Truncate updates mtime.
-			setLocalMtime = true
-			stat.Mtime.Nsec = linux.UTIME_NOW
+
+		// Prepare for truncate.
+		if stat.Mask&linux.STATX_SIZE != 0 {
+			switch d.mode & linux.S_IFMT {
+			case linux.S_IFREG:
+				if !setLocalMtime {
+					// Truncate updates mtime.
+					setLocalMtime = true
+					stat.Mtime.Nsec = linux.UTIME_NOW
+				}
+			case linux.S_IFDIR:
+				return syserror.EISDIR
+			default:
+				return syserror.EINVAL
+			}
 		}
 	}
 	d.metadataMu.Lock()
@@ -1049,6 +1070,7 @@ func (d *dentry) destroyLocked() {
 		d.handle.close(ctx)
 	}
 	d.handleMu.Unlock()
+
 	if !d.file.isNil() {
 		d.file.close(ctx)
 		d.file = p9file{}
@@ -1134,7 +1156,7 @@ func (d *dentry) removexattr(ctx context.Context, creds *auth.Credentials, name
 	return d.file.removeXattr(ctx, name)
 }
 
-// Preconditions: !d.file.isNil(). d.isRegularFile() || d.isDirectory().
+// Preconditions: !d.isSynthetic(). d.isRegularFile() || d.isDirectory().
 func (d *dentry) ensureSharedHandle(ctx context.Context, read, write, trunc bool) error {
 	// O_TRUNC unconditionally requires us to obtain a new handle (opened with
 	// O_TRUNC).