1 files changed, 287 insertions, 0 deletions
diff --git a/pkg/sentry/fsimpl/proc/task_fds.go b/pkg/sentry/fsimpl/proc/task_fds.go
new file mode 100644
index 000000000..76bfc5307
--- /dev/null
+++ b/pkg/sentry/fsimpl/proc/task_fds.go
@@ -0,0 +1,287 @@
+// 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 proc
+
+import (
+	"bytes"
+	"fmt"
+	"sort"
+	"strconv"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/refs"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+type fdDir struct {
+	inoGen InoGenerator
+	task   *kernel.Task
+
+	// When produceSymlinks is set, dirents produces for the FDs are reported
+	// as symlink. Otherwise, they are reported as regular files.
+	produceSymlink bool
+}
+
+func (i *fdDir) lookup(name string) (*vfs.FileDescription, kernel.FDFlags, error) {
+	fd, err := strconv.ParseUint(name, 10, 64)
+	if err != nil {
+		return nil, kernel.FDFlags{}, syserror.ENOENT
+	}
+
+	var (
+		file  *vfs.FileDescription
+		flags kernel.FDFlags
+	)
+	i.task.WithMuLocked(func(t *kernel.Task) {
+		if fdTable := t.FDTable(); fdTable != nil {
+			file, flags = fdTable.GetVFS2(int32(fd))
+		}
+	})
+	if file == nil {
+		return nil, kernel.FDFlags{}, syserror.ENOENT
+	}
+	return file, flags, nil
+}
+
+// IterDirents implements kernfs.inodeDynamicLookup.
+func (i *fdDir) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback, absOffset, relOffset int64) (int64, error) {
+	var fds []int32
+	i.task.WithMuLocked(func(t *kernel.Task) {
+		if fdTable := t.FDTable(); fdTable != nil {
+			fds = fdTable.GetFDs()
+		}
+	})
+
+	offset := absOffset + relOffset
+	typ := uint8(linux.DT_REG)
+	if i.produceSymlink {
+		typ = linux.DT_LNK
+	}
+
+	// Find the appropriate starting point.
+	idx := sort.Search(len(fds), func(i int) bool { return fds[i] >= int32(relOffset) })
+	if idx >= len(fds) {
+		return offset, nil
+	}
+	for _, fd := range fds[idx:] {
+		dirent := vfs.Dirent{
+			Name:    strconv.FormatUint(uint64(fd), 10),
+			Type:    typ,
+			Ino:     i.inoGen.NextIno(),
+			NextOff: offset + 1,
+		}
+		if err := cb.Handle(dirent); err != nil {
+			return offset, err
+		}
+		offset++
+	}
+	return offset, nil
+}
+
+// fdDirInode represents the inode for /proc/[pid]/fd directory.
+//
+// +stateify savable
+type fdDirInode struct {
+	kernfs.InodeNotSymlink
+	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeAttrs
+	kernfs.OrderedChildren
+	kernfs.AlwaysValid
+	fdDir
+}
+
+var _ kernfs.Inode = (*fdDirInode)(nil)
+
+func newFDDirInode(task *kernel.Task, inoGen InoGenerator) *kernfs.Dentry {
+	inode := &fdDirInode{
+		fdDir: fdDir{
+			inoGen:         inoGen,
+			task:           task,
+			produceSymlink: true,
+		},
+	}
+	inode.InodeAttrs.Init(task.Credentials(), inoGen.NextIno(), linux.ModeDirectory|0555)
+
+	dentry := &kernfs.Dentry{}
+	dentry.Init(inode)
+	inode.OrderedChildren.Init(kernfs.OrderedChildrenOptions{})
+
+	return dentry
+}
+
+// Lookup implements kernfs.inodeDynamicLookup.
+func (i *fdDirInode) Lookup(ctx context.Context, name string) (*vfs.Dentry, error) {
+	file, _, err := i.lookup(name)
+	if err != nil {
+		return nil, err
+	}
+	taskDentry := newFDSymlink(i.task.Credentials(), file, i.inoGen.NextIno())
+	return taskDentry.VFSDentry(), nil
+}
+
+// Open implements kernfs.Inode.
+func (i *fdDirInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd := &kernfs.GenericDirectoryFD{}
+	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, &opts)
+	return fd.VFSFileDescription(), nil
+}
+
+// CheckPermissions implements kernfs.Inode.
+//
+// This is to match Linux, which uses a special permission handler to guarantee
+// that a process can still access /proc/self/fd after it has executed
+// setuid. See fs/proc/fd.c:proc_fd_permission.
+func (i *fdDirInode) CheckPermissions(ctx context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	err := i.InodeAttrs.CheckPermissions(ctx, creds, ats)
+	if err == nil {
+		// Access granted, no extra check needed.
+		return nil
+	}
+	if t := kernel.TaskFromContext(ctx); t != nil {
+		// Allow access if the task trying to access it is in the thread group
+		// corresponding to this directory.
+		if i.task.ThreadGroup() == t.ThreadGroup() {
+			// Access granted (overridden).
+			return nil
+		}
+	}
+	return err
+}
+
+// fdSymlink is an symlink for the /proc/[pid]/fd/[fd] file.
+//
+// +stateify savable
+type fdSymlink struct {
+	refs.AtomicRefCount
+	kernfs.InodeAttrs
+	kernfs.InodeSymlink
+
+	file *vfs.FileDescription
+}
+
+var _ kernfs.Inode = (*fdSymlink)(nil)
+
+func newFDSymlink(creds *auth.Credentials, file *vfs.FileDescription, ino uint64) *kernfs.Dentry {
+	file.IncRef()
+	inode := &fdSymlink{file: file}
+	inode.Init(creds, ino, linux.ModeSymlink|0777)
+
+	d := &kernfs.Dentry{}
+	d.Init(inode)
+	return d
+}
+
+func (s *fdSymlink) Readlink(ctx context.Context) (string, error) {
+	root := vfs.RootFromContext(ctx)
+	defer root.DecRef()
+
+	vfsObj := s.file.VirtualDentry().Mount().Filesystem().VirtualFilesystem()
+	return vfsObj.PathnameWithDeleted(ctx, root, s.file.VirtualDentry())
+}
+
+func (s *fdSymlink) DecRef() {
+	s.AtomicRefCount.DecRefWithDestructor(func() {
+		s.Destroy()
+	})
+}
+
+func (s *fdSymlink) Destroy() {
+	s.file.DecRef()
+}
+
+// fdInfoDirInode represents the inode for /proc/[pid]/fdinfo directory.
+//
+// +stateify savable
+type fdInfoDirInode struct {
+	kernfs.InodeNotSymlink
+	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeAttrs
+	kernfs.OrderedChildren
+	kernfs.AlwaysValid
+	fdDir
+}
+
+var _ kernfs.Inode = (*fdInfoDirInode)(nil)
+
+func newFDInfoDirInode(task *kernel.Task, inoGen InoGenerator) *kernfs.Dentry {
+	inode := &fdInfoDirInode{
+		fdDir: fdDir{
+			inoGen: inoGen,
+			task:   task,
+		},
+	}
+	inode.InodeAttrs.Init(task.Credentials(), inoGen.NextIno(), linux.ModeDirectory|0555)
+
+	dentry := &kernfs.Dentry{}
+	dentry.Init(inode)
+	inode.OrderedChildren.Init(kernfs.OrderedChildrenOptions{})
+
+	return dentry
+}
+
+// Lookup implements kernfs.inodeDynamicLookup.
+func (i *fdInfoDirInode) Lookup(ctx context.Context, name string) (*vfs.Dentry, error) {
+	file, flags, err := i.lookup(name)
+	if err != nil {
+		return nil, err
+	}
+
+	data := &fdInfoData{file: file, flags: flags}
+	dentry := newTaskOwnedFile(i.task, i.inoGen.NextIno(), 0444, data)
+	return dentry.VFSDentry(), nil
+}
+
+// Open implements kernfs.Inode.
+func (i *fdInfoDirInode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd := &kernfs.GenericDirectoryFD{}
+	fd.Init(rp.Mount(), vfsd, &i.OrderedChildren, &opts)
+	return fd.VFSFileDescription(), nil
+}
+
+// fdInfoData implements vfs.DynamicBytesSource for /proc/[pid]/fdinfo/[fd].
+//
+// +stateify savable
+type fdInfoData struct {
+	kernfs.DynamicBytesFile
+	refs.AtomicRefCount
+
+	file  *vfs.FileDescription
+	flags kernel.FDFlags
+}
+
+var _ dynamicInode = (*fdInfoData)(nil)
+
+func (d *fdInfoData) DecRef() {
+	d.AtomicRefCount.DecRefWithDestructor(d.destroy)
+}
+
+func (d *fdInfoData) destroy() {
+	d.file.DecRef()
+}
+
+// Generate implements vfs.DynamicBytesSource.Generate.
+func (d *fdInfoData) Generate(ctx context.Context, buf *bytes.Buffer) error {
+	// TODO(b/121266871): Include pos, locks, and other data. For now we only
+	// have flags.
+	// See https://www.kernel.org/doc/Documentation/filesystems/proc.txt
+	flags := uint(d.file.StatusFlags()) | d.flags.ToLinuxFileFlags()
+	fmt.Fprintf(buf, "flags:\t0%o\n", flags)
+	return nil
+}