Implement pipe(2) and pipe2(2) for VFS2.

Updates #1035

PiperOrigin-RevId: 306968644

2 files changed, 168 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/pipefs/BUILD b/pkg/sentry/fsimpl/pipefs/BUILD
new file mode 100644
index 000000000..0d411606f
--- /dev/null
+++ b/pkg/sentry/fsimpl/pipefs/BUILD
@@ -0,0 +1,20 @@
+load("//tools:defs.bzl", "go_library")
+
+licenses(["notice"])
+
+go_library(
+    name = "pipefs",
+    srcs = ["pipefs.go"],
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/abi/linux",
+        "//pkg/context",
+        "//pkg/sentry/fsimpl/kernfs",
+        "//pkg/sentry/kernel/auth",
+        "//pkg/sentry/kernel/pipe",
+        "//pkg/sentry/kernel/time",
+        "//pkg/sentry/vfs",
+        "//pkg/syserror",
+        "//pkg/usermem",
+    ],
+)
diff --git a/pkg/sentry/fsimpl/pipefs/pipefs.go b/pkg/sentry/fsimpl/pipefs/pipefs.go
new file mode 100644
index 000000000..faf3179bc
--- /dev/null
+++ b/pkg/sentry/fsimpl/pipefs/pipefs.go
@@ -0,0 +1,148 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package pipefs provides the filesystem implementation backing
+// Kernel.PipeMount.
+package pipefs
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"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/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+type filesystemType struct{}
+
+// Name implements vfs.FilesystemType.Name.
+func (filesystemType) Name() string {
+	return "pipefs"
+}
+
+// GetFilesystem implements vfs.FilesystemType.GetFilesystem.
+func (filesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+	panic("pipefs.filesystemType.GetFilesystem should never be called")
+}
+
+// filesystem implements vfs.FilesystemImpl.
+type filesystem struct {
+	kernfs.Filesystem
+
+	// TODO(gvisor.dev/issue/1193):
+	//
+	// - kernfs does not provide a way to implement statfs, from which we
+	// should indicate PIPEFS_MAGIC.
+	//
+	// - kernfs does not provide a way to override names for
+	// vfs.FilesystemImpl.PrependPath(); pipefs inodes should use synthetic
+	// name fmt.Sprintf("pipe:[%d]", inode.ino).
+}
+
+// NewFilesystem sets up and returns a new vfs.Filesystem implemented by
+// pipefs.
+func NewFilesystem(vfsObj *vfs.VirtualFilesystem) *vfs.Filesystem {
+	fs := &filesystem{}
+	fs.Init(vfsObj, filesystemType{})
+	return fs.VFSFilesystem()
+}
+
+// inode implements kernfs.Inode.
+type inode struct {
+	kernfs.InodeNotDirectory
+	kernfs.InodeNotSymlink
+	kernfs.InodeNoopRefCount
+
+	pipe *pipe.VFSPipe
+
+	ino uint64
+	uid auth.KUID
+	gid auth.KGID
+	// We use the creation timestamp for all of atime, mtime, and ctime.
+	ctime ktime.Time
+}
+
+func newInode(ctx context.Context, fs *kernfs.Filesystem) *inode {
+	creds := auth.CredentialsFromContext(ctx)
+	return &inode{
+		pipe:  pipe.NewVFSPipe(false /* isNamed */, pipe.DefaultPipeSize, usermem.PageSize),
+		ino:   fs.NextIno(),
+		uid:   creds.EffectiveKUID,
+		gid:   creds.EffectiveKGID,
+		ctime: ktime.NowFromContext(ctx),
+	}
+}
+
+const pipeMode = 0600 | linux.S_IFIFO
+
+// CheckPermissions implements kernfs.Inode.CheckPermissions.
+func (i *inode) CheckPermissions(ctx context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	return vfs.GenericCheckPermissions(creds, ats, pipeMode, i.uid, i.gid)
+}
+
+// Mode implements kernfs.Inode.Mode.
+func (i *inode) Mode() linux.FileMode {
+	return pipeMode
+}
+
+// Stat implements kernfs.Inode.Stat.
+func (i *inode) Stat(vfsfs *vfs.Filesystem, opts vfs.StatOptions) (linux.Statx, error) {
+	ts := linux.NsecToStatxTimestamp(i.ctime.Nanoseconds())
+	return linux.Statx{
+		Mask:    linux.STATX_TYPE | linux.STATX_MODE | linux.STATX_NLINK | linux.STATX_UID | linux.STATX_GID | linux.STATX_ATIME | linux.STATX_MTIME | linux.STATX_CTIME | linux.STATX_INO | linux.STATX_SIZE | linux.STATX_BLOCKS,
+		Blksize: usermem.PageSize,
+		Nlink:   1,
+		UID:     uint32(i.uid),
+		GID:     uint32(i.gid),
+		Mode:    pipeMode,
+		Ino:     i.ino,
+		Size:    0,
+		Blocks:  0,
+		Atime:   ts,
+		Ctime:   ts,
+		Mtime:   ts,
+		// TODO(gvisor.dev/issue/1197): Device number.
+	}, nil
+}
+
+// SetStat implements kernfs.Inode.SetStat.
+func (i *inode) SetStat(ctx context.Context, vfsfs *vfs.Filesystem, creds *auth.Credentials, opts vfs.SetStatOptions) error {
+	if opts.Stat.Mask == 0 {
+		return nil
+	}
+	return syserror.EPERM
+}
+
+// Open implements kernfs.Inode.Open.
+func (i *inode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	// FIXME(b/38173783): kernfs does not plumb Context here.
+	return i.pipe.Open(context.Background(), rp.Mount(), vfsd, opts.Flags)
+}
+
+// NewConnectedPipeFDs returns a pair of FileDescriptions representing the read
+// and write ends of a newly-created pipe, as for pipe(2) and pipe2(2).
+//
+// Preconditions: mnt.Filesystem() must have been returned by NewFilesystem().
+func NewConnectedPipeFDs(ctx context.Context, mnt *vfs.Mount, flags uint32) (*vfs.FileDescription, *vfs.FileDescription) {
+	fs := mnt.Filesystem().Impl().(*kernfs.Filesystem)
+	inode := newInode(ctx, fs)
+	var d kernfs.Dentry
+	d.Init(inode)
+	defer d.DecRef()
+	return inode.pipe.ReaderWriterPair(mnt, d.VFSDentry(), flags)
+}