Fixes for procfs

- Return ENOENT for /proc/[pid]/task if task is zoombied or terminated
- Allow directory to be Seek() to the end
- Construct synthetic files for /proc/[pid]/ns/*
- Changed GenericDirectoryFD.Init to not register with FileDescription,
  otherwise other implementation cannot change behavior.

Updates #1195,1193

PiperOrigin-RevId: 308294649

6 files changed, 38 insertions, 16 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
index e8a4670b8..dd5806301 100644
--- a/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/fd_impl_util.go
@@ -15,6 +15,8 @@
 package kernfs
 
 import (
+	"math"
+
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
@@ -43,15 +45,27 @@ type GenericDirectoryFD struct {
 	off      int64
 }
 
-// Init initializes a GenericDirectoryFD.
-func (fd *GenericDirectoryFD) Init(m *vfs.Mount, d *vfs.Dentry, children *OrderedChildren, opts *vfs.OpenOptions) error {
+// NewGenericDirectoryFD creates a new GenericDirectoryFD and returns its
+// dentry.
+func NewGenericDirectoryFD(m *vfs.Mount, d *vfs.Dentry, children *OrderedChildren, opts *vfs.OpenOptions) (*GenericDirectoryFD, error) {
+	fd := &GenericDirectoryFD{}
+	if err := fd.Init(children, opts); err != nil {
+		return nil, err
+	}
+	if err := fd.vfsfd.Init(fd, opts.Flags, m, d, &vfs.FileDescriptionOptions{}); err != nil {
+		return nil, err
+	}
+	return fd, nil
+}
+
+// Init initializes a GenericDirectoryFD. Use it when overriding
+// GenericDirectoryFD. Caller must call fd.VFSFileDescription.Init() with the
+// correct implementation.
+func (fd *GenericDirectoryFD) Init(children *OrderedChildren, opts *vfs.OpenOptions) error {
 	if vfs.AccessTypesForOpenFlags(opts)&vfs.MayWrite != 0 {
 		// Can't open directories for writing.
 		return syserror.EISDIR
 	}
-	if err := fd.vfsfd.Init(fd, opts.Flags, m, d, &vfs.FileDescriptionOptions{}); err != nil {
-		return err
-	}
 	fd.children = children
 	return nil
 }
@@ -187,6 +201,10 @@ func (fd *GenericDirectoryFD) Seek(ctx context.Context, offset int64, whence int
 		// Use offset as given.
 	case linux.SEEK_CUR:
 		offset += fd.off
+	case linux.SEEK_END:
+		// TODO(gvisor.dev/issue/1193): This can prevent new files from showing up
+		// if they are added after SEEK_END.
+		offset = math.MaxInt64
 	default:
 		return 0, syserror.EINVAL
 	}
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index 1d46dba25..3ccd92fc5 100644
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
@@ -82,7 +82,7 @@ afterSymlink:
 	}
 	// Resolve any symlink at current path component.
 	if rp.ShouldFollowSymlink() && next.isSymlink() {
-		targetVD, targetPathname, err := next.inode.Getlink(ctx)
+		targetVD, targetPathname, err := next.inode.Getlink(ctx, rp.Mount())
 		if err != nil {
 			return nil, err
 		}
@@ -477,7 +477,7 @@ afterTrailingSymlink:
 	}
 	child := childVFSD.Impl().(*Dentry)
 	if rp.ShouldFollowSymlink() && child.isSymlink() {
-		targetVD, targetPathname, err := child.inode.Getlink(ctx)
+		targetVD, targetPathname, err := child.inode.Getlink(ctx, rp.Mount())
 		if err != nil {
 			return nil, err
 		}
diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
index a946645f6..02f35a675 100644
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
@@ -182,7 +182,7 @@ func (InodeNotSymlink) Readlink(context.Context) (string, error) {
 }
 
 // Getlink implements Inode.Getlink.
-func (InodeNotSymlink) Getlink(context.Context) (vfs.VirtualDentry, string, error) {
+func (InodeNotSymlink) Getlink(context.Context, *vfs.Mount) (vfs.VirtualDentry, string, error) {
 	return vfs.VirtualDentry{}, "", syserror.EINVAL
 }
 
@@ -568,8 +568,10 @@ func (s *StaticDirectory) Init(creds *auth.Credentials, ino uint64, perm linux.F
 
 // Open implements kernfs.Inode.
 func (s *StaticDirectory) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
-	fd := &GenericDirectoryFD{}
-	fd.Init(rp.Mount(), vfsd, &s.OrderedChildren, &opts)
+	fd, err := NewGenericDirectoryFD(rp.Mount(), vfsd, &s.OrderedChildren, &opts)
+	if err != nil {
+		return nil, err
+	}
 	return fd.VFSFileDescription(), nil
 }
 
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index f5041824f..95cf6dc24 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -439,5 +439,5 @@ type inodeSymlink interface {
 	//
 	// - If the inode is not a symlink, Getlink returns (zero-value
 	// VirtualDentry, "", EINVAL).
-	Getlink(ctx context.Context) (vfs.VirtualDentry, string, error)
+	Getlink(ctx context.Context, mnt *vfs.Mount) (vfs.VirtualDentry, string, error)
 }
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs_test.go b/pkg/sentry/fsimpl/kernfs/kernfs_test.go
index 465451f35..0964d5456 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs_test.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs_test.go
@@ -117,8 +117,8 @@ func (fs *filesystem) newReadonlyDir(creds *auth.Credentials, mode linux.FileMod
 }
 
 func (d *readonlyDir) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
-	fd := &kernfs.GenericDirectoryFD{}
-	if err := fd.Init(rp.Mount(), vfsd, &d.OrderedChildren, &opts); err != nil {
+	fd, err := kernfs.NewGenericDirectoryFD(rp.Mount(), vfsd, &d.OrderedChildren, &opts)
+	if err != nil {
 		return nil, err
 	}
 	return fd.VFSFileDescription(), nil
@@ -147,8 +147,10 @@ func (fs *filesystem) newDir(creds *auth.Credentials, mode linux.FileMode, conte
 }
 
 func (d *dir) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
-	fd := &kernfs.GenericDirectoryFD{}
-	fd.Init(rp.Mount(), vfsd, &d.OrderedChildren, &opts)
+	fd, err := kernfs.NewGenericDirectoryFD(rp.Mount(), vfsd, &d.OrderedChildren, &opts)
+	if err != nil {
+		return nil, err
+	}
 	return fd.VFSFileDescription(), nil
 }
 
diff --git a/pkg/sentry/fsimpl/kernfs/symlink.go b/pkg/sentry/fsimpl/kernfs/symlink.go
index 018aa503c..0aa6dc979 100644
--- a/pkg/sentry/fsimpl/kernfs/symlink.go
+++ b/pkg/sentry/fsimpl/kernfs/symlink.go
@@ -56,7 +56,7 @@ func (s *StaticSymlink) Readlink(_ context.Context) (string, error) {
 }
 
 // Getlink implements Inode.Getlink.
-func (s *StaticSymlink) Getlink(_ context.Context) (vfs.VirtualDentry, string, error) {
+func (s *StaticSymlink) Getlink(context.Context, *vfs.Mount) (vfs.VirtualDentry, string, error) {
 	return vfs.VirtualDentry{}, s.target, nil
 }