Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 258 insertions, 0 deletions

diff --git a/pkg/sentry/fs/proc/fds.go b/pkg/sentry/fs/proc/fds.go
new file mode 100644
index 000000000..2eca9ac31
--- /dev/null
+++ b/pkg/sentry/fs/proc/fds.go
@@ -0,0 +1,258 @@
+// Copyright 2018 Google Inc.
+//
+// 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 (
+	"fmt"
+	"sort"
+	"strconv"
+
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/proc/device"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/ramfs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/kdefs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+)
+
+// walkDescriptors finds the descriptor (file-flag pair) for the fd identified
+// by p, and calls the toInodeOperations callback with that descriptor.  This is a helper
+// method for implementing fs.InodeOperations.Lookup.
+func walkDescriptors(t *kernel.Task, p string, toInode func(*fs.File, kernel.FDFlags) *fs.Inode) (*fs.Inode, error) {
+	n, err := strconv.ParseUint(p, 10, 64)
+	if err != nil {
+		// Not found.
+		return nil, syserror.ENOENT
+	}
+
+	var file *fs.File
+	var flags kernel.FDFlags
+	t.WithMuLocked(func(t *kernel.Task) {
+		if fdm := t.FDMap(); fdm != nil {
+			file, flags = fdm.GetDescriptor(kdefs.FD(n))
+		}
+	})
+	if file == nil {
+		return nil, syserror.ENOENT
+	}
+	return toInode(file, flags), nil
+}
+
+// readDescriptors reads fds in the task starting at offset, and calls the
+// toDentAttr callback for each to get a DentAttr, which it then emits. This is
+// a helper for implementing fs.InodeOperations.Readdir.
+func readDescriptors(t *kernel.Task, c *fs.DirCtx, offset int, toDentAttr func(int) fs.DentAttr) (int, error) {
+	var fds kernel.FDs
+	t.WithMuLocked(func(t *kernel.Task) {
+		if fdm := t.FDMap(); fdm != nil {
+			fds = fdm.GetFDs()
+		}
+	})
+
+	fdInts := make([]int, 0, len(fds))
+	for _, fd := range fds {
+		fdInts = append(fdInts, int(fd))
+	}
+
+	// Find the fd to start at.
+	idx := sort.SearchInts(fdInts, offset)
+	if idx == len(fdInts) {
+		return offset, nil
+	}
+	fdInts = fdInts[idx:]
+
+	var fd int
+	for _, fd = range fdInts {
+		name := strconv.FormatUint(uint64(fd), 10)
+		if err := c.DirEmit(name, toDentAttr(fd)); err != nil {
+			// Returned offset is the next fd to serialize.
+			return fd, err
+		}
+	}
+	// We serialized them all.  Next offset should be higher than last
+	// serialized fd.
+	return fd + 1, nil
+}
+
+// fd is a single file in /proc/TID/fd/.
+type fd struct {
+	ramfs.Symlink
+	*fs.File
+}
+
+// newFD returns a new fd based on an existing file.
+//
+// This inherits one reference to the file.
+func newFd(t *kernel.Task, f *fs.File, msrc *fs.MountSource) *fs.Inode {
+	fd := &fd{File: f}
+	// RootOwner by default, is overridden in UnstableAttr()
+	fd.InitSymlink(t, fs.RootOwner, "")
+	return newFile(fd, msrc, fs.Symlink, t)
+}
+
+// GetFile returns the fs.File backing this fd.  The dirent and flags
+// arguments are ignored.
+func (f *fd) GetFile(context.Context, *fs.Dirent, fs.FileFlags) (*fs.File, error) {
+	// Take a reference on the fs.File.
+	f.File.IncRef()
+	return f.File, nil
+}
+
+// Readlink returns the current target.
+func (f *fd) Readlink(ctx context.Context, _ *fs.Inode) (string, error) {
+	root := fs.RootFromContext(ctx)
+	defer root.DecRef()
+	n, _ := f.Dirent.FullName(root)
+	return n, nil
+}
+
+// Getlink implements fs.InodeOperations.Getlink.
+func (f *fd) Getlink(context.Context, *fs.Inode) (*fs.Dirent, error) {
+	f.Dirent.IncRef()
+	return f.Dirent, nil
+}
+
+// Truncate is ignored.
+func (f *fd) Truncate(context.Context, *fs.Inode, int64) error {
+	return nil
+}
+
+// Close releases the reference on the file.
+func (f *fd) Close() error {
+	f.DecRef()
+	return nil
+}
+
+// fdDir implements /proc/TID/fd.
+type fdDir struct {
+	ramfs.Dir
+
+	// We hold a reference on the task's fdmap but only keep an indirect
+	// task pointer to avoid Dirent loading circularity caused by fdmap's
+	// potential back pointers into the dirent tree.
+	t *kernel.Task
+}
+
+// newFdDir creates a new fdDir.
+func newFdDir(t *kernel.Task, msrc *fs.MountSource) *fs.Inode {
+	f := &fdDir{t: t}
+	f.InitDir(t, nil, fs.RootOwner, fs.FilePermissions{User: fs.PermMask{Read: true, Execute: true}})
+	return newFile(f, msrc, fs.SpecialDirectory, t)
+}
+
+// Check implements InodeOperations.Check.
+//
+// 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 (f *fdDir) Check(ctx context.Context, inode *fs.Inode, req fs.PermMask) bool {
+	if fs.ContextCanAccessFile(ctx, inode, req) {
+		return true
+	}
+	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.
+		//
+		// N.B. Technically, in Linux 3.11, this compares what would be
+		// the equivalent of task pointers. However, this was fixed
+		// later in 54708d2858e7 ("proc: actually make
+		// proc_fd_permission() thread-friendly").
+		if f.t.ThreadGroup() == t.ThreadGroup() {
+			return true
+		}
+	}
+	return false
+}
+
+// Lookup loads an Inode in /proc/TID/fd into a Dirent.
+func (f *fdDir) Lookup(ctx context.Context, dir *fs.Inode, p string) (*fs.Dirent, error) {
+	n, err := walkDescriptors(f.t, p, func(file *fs.File, _ kernel.FDFlags) *fs.Inode {
+		return newFd(f.t, file, dir.MountSource)
+	})
+	if err != nil {
+		return nil, err
+	}
+	return fs.NewDirent(n, p), nil
+}
+
+// DeprecatedReaddir lists fds in /proc/TID/fd.
+func (f *fdDir) DeprecatedReaddir(ctx context.Context, dirCtx *fs.DirCtx, offset int) (int, error) {
+	return readDescriptors(f.t, dirCtx, offset, func(fd int) fs.DentAttr {
+		return fs.GenericDentAttr(fs.Symlink, device.ProcDevice)
+	})
+}
+
+// fdInfo is a single file in /proc/TID/fdinfo/.
+type fdInfo struct {
+	ramfs.File
+
+	flags kernel.FDFlags
+}
+
+// newFdInfo returns a new fdInfo based on an existing file.
+func newFdInfo(t *kernel.Task, _ *fs.File, flags kernel.FDFlags, msrc *fs.MountSource) *fs.Inode {
+	fdi := &fdInfo{flags: flags}
+	fdi.InitFile(t, fs.RootOwner, fs.FilePermissions{User: fs.PermMask{Read: true}})
+	// TODO: Get pos, locks, and other data.  For now we only
+	// have flags.
+	// See https://www.kernel.org/doc/Documentation/filesystems/proc.txt
+	fdi.Append([]byte(fmt.Sprintf("flags: %08o\n", flags)))
+	return newFile(fdi, msrc, fs.SpecialFile, t)
+}
+
+// DeprecatedPwritev implements fs.HandleOperations.DeprecatedPwritev.
+func (*fdInfo) DeprecatedPwritev(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
+	return 0, ramfs.ErrInvalidOp
+}
+
+// Truncate implements fs.InodeOperations.Truncate.
+func (*fdInfo) Truncate(ctx context.Context, inode *fs.Inode, size int64) error {
+	return ramfs.ErrInvalidOp
+}
+
+// fdInfoDir implements /proc/TID/fdinfo.  It embeds an fdDir, but overrides
+// Lookup and Readdir.
+type fdInfoDir struct {
+	ramfs.Dir
+
+	t *kernel.Task
+}
+
+// newFdInfoDir creates a new fdInfoDir.
+func newFdInfoDir(t *kernel.Task, msrc *fs.MountSource) *fs.Inode {
+	fdid := &fdInfoDir{t: t}
+	fdid.InitDir(t, nil, fs.RootOwner, fs.FilePermsFromMode(0500))
+	return newFile(fdid, msrc, fs.SpecialDirectory, t)
+}
+
+// Lookup loads an fd in /proc/TID/fdinfo into a Dirent.
+func (fdid *fdInfoDir) Lookup(ctx context.Context, dir *fs.Inode, p string) (*fs.Dirent, error) {
+	n, err := walkDescriptors(fdid.t, p, func(file *fs.File, flags kernel.FDFlags) *fs.Inode {
+		return newFdInfo(fdid.t, file, flags, dir.MountSource)
+	})
+	if err != nil {
+		return nil, err
+	}
+	return fs.NewDirent(n, p), nil
+}
+
+// DeprecatedReaddir lists fds in /proc/TID/fdinfo.
+func (fdid *fdInfoDir) DeprecatedReaddir(ctx context.Context, dirCtx *fs.DirCtx, offset int) (int, error) {
+	return readDescriptors(fdid.t, dirCtx, offset, func(fd int) fs.DentAttr {
+		return fs.GenericDentAttr(fs.RegularFile, device.ProcDevice)
+	})
+}