From 4a428b13b20baf055e7e70ecb51a87299f0c6d8e Mon Sep 17 00:00:00 2001
From: Fabricio Voznika <fvoznika@google.com>
Date: Tue, 29 Sep 2020 15:47:25 -0700
Subject: Add /proc/[pid]/cwd
PiperOrigin-RevId: 334478850
---
pkg/sentry/fs/proc/task.go | 44 ++++++++++++++
pkg/sentry/fsimpl/proc/task.go | 1 +
pkg/sentry/fsimpl/proc/task_files.go | 107 +++++++++++++++++++++++++++--------
pkg/sentry/fsimpl/proc/tasks_test.go | 1 +
4 files changed, 129 insertions(+), 24 deletions(-)
(limited to 'pkg')
diff --git a/pkg/sentry/fs/proc/task.go b/pkg/sentry/fs/proc/task.go
index 103bfc600..22d658acf 100644
--- a/pkg/sentry/fs/proc/task.go
+++ b/pkg/sentry/fs/proc/task.go
@@ -84,6 +84,7 @@ func (p *proc) newTaskDir(t *kernel.Task, msrc *fs.MountSource, isThreadGroup bo
"auxv": newAuxvec(t, msrc),
"cmdline": newExecArgInode(t, msrc, cmdlineExecArg),
"comm": newComm(t, msrc),
+ "cwd": newCwd(t, msrc),
"environ": newExecArgInode(t, msrc, environExecArg),
"exe": newExe(t, msrc),
"fd": newFdDir(t, msrc),
@@ -300,6 +301,49 @@ func (e *exe) Readlink(ctx context.Context, inode *fs.Inode) (string, error) {
return exec.PathnameWithDeleted(ctx), nil
}
+// cwd is an fs.InodeOperations symlink for the /proc/PID/cwd file.
+//
+// +stateify savable
+type cwd struct {
+ ramfs.Symlink
+
+ t *kernel.Task
+}
+
+func newCwd(t *kernel.Task, msrc *fs.MountSource) *fs.Inode {
+ cwdSymlink := &cwd{
+ Symlink: *ramfs.NewSymlink(t, fs.RootOwner, ""),
+ t: t,
+ }
+ return newProcInode(t, cwdSymlink, msrc, fs.Symlink, t)
+}
+
+// Readlink implements fs.InodeOperations.
+func (e *cwd) Readlink(ctx context.Context, inode *fs.Inode) (string, error) {
+ if !kernel.ContextCanTrace(ctx, e.t, false) {
+ return "", syserror.EACCES
+ }
+ if err := checkTaskState(e.t); err != nil {
+ return "", err
+ }
+ cwd := e.t.FSContext().WorkingDirectory()
+ if cwd == nil {
+ // It could have raced with process deletion.
+ return "", syserror.ESRCH
+ }
+ defer cwd.DecRef(ctx)
+
+ root := fs.RootFromContext(ctx)
+ if root == nil {
+ // It could have raced with process deletion.
+ return "", syserror.ESRCH
+ }
+ defer root.DecRef(ctx)
+
+ name, _ := cwd.FullName(root)
+ return name, nil
+}
+
// namespaceSymlink represents a symlink in the namespacefs, such as the files
// in /proc/<pid>/ns.
//
diff --git a/pkg/sentry/fsimpl/proc/task.go b/pkg/sentry/fsimpl/proc/task.go
index 1f99183eb..a7cd6f57e 100644
--- a/pkg/sentry/fsimpl/proc/task.go
+++ b/pkg/sentry/fsimpl/proc/task.go
@@ -53,6 +53,7 @@ func (fs *filesystem) newTaskInode(task *kernel.Task, pidns *kernel.PIDNamespace
"auxv": fs.newTaskOwnedFile(task, fs.NextIno(), 0444, &auxvData{task: task}),
"cmdline": fs.newTaskOwnedFile(task, fs.NextIno(), 0444, &cmdlineData{task: task, arg: cmdlineDataArg}),
"comm": fs.newComm(task, fs.NextIno(), 0444),
+ "cwd": fs.newCwdSymlink(task, fs.NextIno()),
"environ": fs.newTaskOwnedFile(task, fs.NextIno(), 0444, &cmdlineData{task: task, arg: environDataArg}),
"exe": fs.newExeSymlink(task, fs.NextIno()),
"fd": fs.newFDDirInode(task),
diff --git a/pkg/sentry/fsimpl/proc/task_files.go b/pkg/sentry/fsimpl/proc/task_files.go
index b81c8279e..3fbf081a6 100644
--- a/pkg/sentry/fsimpl/proc/task_files.go
+++ b/pkg/sentry/fsimpl/proc/task_files.go
@@ -669,18 +669,22 @@ func (fs *filesystem) newExeSymlink(task *kernel.Task, ino uint64) *kernfs.Dentr
// Readlink implements kernfs.Inode.Readlink.
func (s *exeSymlink) Readlink(ctx context.Context, _ *vfs.Mount) (string, error) {
- if !kernel.ContextCanTrace(ctx, s.task, false) {
- return "", syserror.EACCES
- }
-
- // Pull out the executable for /proc/[pid]/exe.
- exec, err := s.executable()
+ exec, _, err := s.Getlink(ctx, nil)
if err != nil {
return "", err
}
defer exec.DecRef(ctx)
- return exec.PathnameWithDeleted(ctx), nil
+ root := vfs.RootFromContext(ctx)
+ if !root.Ok() {
+ // It could have raced with process deletion.
+ return "", syserror.ESRCH
+ }
+ defer root.DecRef(ctx)
+
+ vfsObj := exec.Mount().Filesystem().VirtualFilesystem()
+ name, _ := vfsObj.PathnameWithDeleted(ctx, root, exec)
+ return name, nil
}
// Getlink implements kernfs.Inode.Getlink.
@@ -688,23 +692,12 @@ func (s *exeSymlink) Getlink(ctx context.Context, _ *vfs.Mount) (vfs.VirtualDent
if !kernel.ContextCanTrace(ctx, s.task, false) {
return vfs.VirtualDentry{}, "", syserror.EACCES
}
-
- exec, err := s.executable()
- if err != nil {
- return vfs.VirtualDentry{}, "", err
- }
- defer exec.DecRef(ctx)
-
- vd := exec.(*fsbridge.VFSFile).FileDescription().VirtualDentry()
- vd.IncRef()
- return vd, "", nil
-}
-
-func (s *exeSymlink) executable() (file fsbridge.File, err error) {
if err := checkTaskState(s.task); err != nil {
- return nil, err
+ return vfs.VirtualDentry{}, "", err
}
+ var err error
+ var exec fsbridge.File
s.task.WithMuLocked(func(t *kernel.Task) {
mm := t.MemoryManager()
if mm == nil {
@@ -715,12 +708,78 @@ func (s *exeSymlink) executable() (file fsbridge.File, err error) {
// The MemoryManager may be destroyed, in which case
// MemoryManager.destroy will simply set the executable to nil
// (with locks held).
- file = mm.Executable()
- if file == nil {
+ exec = mm.Executable()
+ if exec == nil {
err = syserror.ESRCH
}
})
- return
+ if err != nil {
+ return vfs.VirtualDentry{}, "", err
+ }
+ defer exec.DecRef(ctx)
+
+ vd := exec.(*fsbridge.VFSFile).FileDescription().VirtualDentry()
+ vd.IncRef()
+ return vd, "", nil
+}
+
+// cwdSymlink is an symlink for the /proc/[pid]/cwd file.
+//
+// +stateify savable
+type cwdSymlink struct {
+ implStatFS
+ kernfs.InodeAttrs
+ kernfs.InodeNoopRefCount
+ kernfs.InodeSymlink
+
+ task *kernel.Task
+}
+
+var _ kernfs.Inode = (*cwdSymlink)(nil)
+
+func (fs *filesystem) newCwdSymlink(task *kernel.Task, ino uint64) *kernfs.Dentry {
+ inode := &cwdSymlink{task: task}
+ inode.Init(task.Credentials(), linux.UNNAMED_MAJOR, fs.devMinor, ino, linux.ModeSymlink|0777)
+
+ d := &kernfs.Dentry{}
+ d.Init(inode)
+ return d
+}
+
+// Readlink implements kernfs.Inode.Readlink.
+func (s *cwdSymlink) Readlink(ctx context.Context, _ *vfs.Mount) (string, error) {
+ cwd, _, err := s.Getlink(ctx, nil)
+ if err != nil {
+ return "", err
+ }
+ defer cwd.DecRef(ctx)
+
+ root := vfs.RootFromContext(ctx)
+ if !root.Ok() {
+ // It could have raced with process deletion.
+ return "", syserror.ESRCH
+ }
+ defer root.DecRef(ctx)
+
+ vfsObj := cwd.Mount().Filesystem().VirtualFilesystem()
+ name, _ := vfsObj.PathnameWithDeleted(ctx, root, cwd)
+ return name, nil
+}
+
+// Getlink implements kernfs.Inode.Getlink.
+func (s *cwdSymlink) Getlink(ctx context.Context, _ *vfs.Mount) (vfs.VirtualDentry, string, error) {
+ if !kernel.ContextCanTrace(ctx, s.task, false) {
+ return vfs.VirtualDentry{}, "", syserror.EACCES
+ }
+ if err := checkTaskState(s.task); err != nil {
+ return vfs.VirtualDentry{}, "", err
+ }
+ cwd := s.task.FSContext().WorkingDirectoryVFS2()
+ if !cwd.Ok() {
+ // It could have raced with process deletion.
+ return vfs.VirtualDentry{}, "", syserror.ESRCH
+ }
+ return cwd, "", nil
}
// mountInfoData is used to implement /proc/[pid]/mountinfo.
diff --git a/pkg/sentry/fsimpl/proc/tasks_test.go b/pkg/sentry/fsimpl/proc/tasks_test.go
index f693f9060..6975af5a7 100644
--- a/pkg/sentry/fsimpl/proc/tasks_test.go
+++ b/pkg/sentry/fsimpl/proc/tasks_test.go
@@ -67,6 +67,7 @@ var (
taskStaticFiles = map[string]testutil.DirentType{
"auxv": linux.DT_REG,
"cgroup": linux.DT_REG,
+ "cwd": linux.DT_LNK,
"cmdline": linux.DT_REG,
"comm": linux.DT_REG,
"environ": linux.DT_REG,
--
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