Merge release-20200323.0-75-gdd98fdd (automated)

6 files changed, 71 insertions, 29 deletions

diff --git a/pkg/sentry/fsbridge/fsbridge_state_autogen.go b/pkg/sentry/fsbridge/fsbridge_state_autogen.go
index 51b57d859..d370b2d47 100755
--- a/pkg/sentry/fsbridge/fsbridge_state_autogen.go
+++ b/pkg/sentry/fsbridge/fsbridge_state_autogen.go
@@ -32,14 +32,14 @@ func (x *fsLookup) load(m state.Map) {
 	m.Load("workingDir", &x.workingDir)
 }
 
-func (x *vfsFile) beforeSave() {}
-func (x *vfsFile) save(m state.Map) {
+func (x *VFSFile) beforeSave() {}
+func (x *VFSFile) save(m state.Map) {
 	x.beforeSave()
 	m.Save("file", &x.file)
 }
 
-func (x *vfsFile) afterLoad() {}
-func (x *vfsFile) load(m state.Map) {
+func (x *VFSFile) afterLoad() {}
+func (x *VFSFile) load(m state.Map) {
 	m.Load("file", &x.file)
 }
 
@@ -61,6 +61,6 @@ func (x *vfsLookup) load(m state.Map) {
 func init() {
 	state.Register("pkg/sentry/fsbridge.fsFile", (*fsFile)(nil), state.Fns{Save: (*fsFile).save, Load: (*fsFile).load})
 	state.Register("pkg/sentry/fsbridge.fsLookup", (*fsLookup)(nil), state.Fns{Save: (*fsLookup).save, Load: (*fsLookup).load})
-	state.Register("pkg/sentry/fsbridge.vfsFile", (*vfsFile)(nil), state.Fns{Save: (*vfsFile).save, Load: (*vfsFile).load})
+	state.Register("pkg/sentry/fsbridge.VFSFile", (*VFSFile)(nil), state.Fns{Save: (*VFSFile).save, Load: (*VFSFile).load})
 	state.Register("pkg/sentry/fsbridge.vfsLookup", (*vfsLookup)(nil), state.Fns{Save: (*vfsLookup).save, Load: (*vfsLookup).load})
 }
diff --git a/pkg/sentry/fsbridge/vfs.go b/pkg/sentry/fsbridge/vfs.go
index 79b808359..89168220a 100755
--- a/pkg/sentry/fsbridge/vfs.go
+++ b/pkg/sentry/fsbridge/vfs.go
@@ -26,22 +26,22 @@ import (
 	"gvisor.dev/gvisor/pkg/usermem"
 )
 
-// fsFile implements File interface over vfs.FileDescription.
+// VFSFile implements File interface over vfs.FileDescription.
 //
 // +stateify savable
-type vfsFile struct {
+type VFSFile struct {
 	file *vfs.FileDescription
 }
 
-var _ File = (*vfsFile)(nil)
+var _ File = (*VFSFile)(nil)
 
 // NewVFSFile creates a new File over fs.File.
 func NewVFSFile(file *vfs.FileDescription) File {
-	return &vfsFile{file: file}
+	return &VFSFile{file: file}
 }
 
 // PathnameWithDeleted implements File.
-func (f *vfsFile) PathnameWithDeleted(ctx context.Context) string {
+func (f *VFSFile) PathnameWithDeleted(ctx context.Context) string {
 	root := vfs.RootFromContext(ctx)
 	defer root.DecRef()
 
@@ -51,7 +51,7 @@ func (f *vfsFile) PathnameWithDeleted(ctx context.Context) string {
 }
 
 // ReadFull implements File.
-func (f *vfsFile) ReadFull(ctx context.Context, dst usermem.IOSequence, offset int64) (int64, error) {
+func (f *VFSFile) ReadFull(ctx context.Context, dst usermem.IOSequence, offset int64) (int64, error) {
 	var total int64
 	for dst.NumBytes() > 0 {
 		n, err := f.file.PRead(ctx, dst, offset+total, vfs.ReadOptions{})
@@ -67,12 +67,12 @@ func (f *vfsFile) ReadFull(ctx context.Context, dst usermem.IOSequence, offset i
 }
 
 // ConfigureMMap implements File.
-func (f *vfsFile) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+func (f *VFSFile) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
 	return f.file.ConfigureMMap(ctx, opts)
 }
 
 // Type implements File.
-func (f *vfsFile) Type(ctx context.Context) (linux.FileMode, error) {
+func (f *VFSFile) Type(ctx context.Context) (linux.FileMode, error) {
 	stat, err := f.file.Stat(ctx, vfs.StatOptions{})
 	if err != nil {
 		return 0, err
@@ -81,15 +81,21 @@ func (f *vfsFile) Type(ctx context.Context) (linux.FileMode, error) {
 }
 
 // IncRef implements File.
-func (f *vfsFile) IncRef() {
+func (f *VFSFile) IncRef() {
 	f.file.IncRef()
 }
 
 // DecRef implements File.
-func (f *vfsFile) DecRef() {
+func (f *VFSFile) DecRef() {
 	f.file.DecRef()
 }
 
+// FileDescription returns the FileDescription represented by f. It does not
+// take an additional reference on the returned FileDescription.
+func (f *VFSFile) FileDescription() *vfs.FileDescription {
+	return f.file
+}
+
 // fsLookup implements Lookup interface using fs.File.
 //
 // +stateify savable
@@ -132,5 +138,5 @@ func (l *vfsLookup) OpenPath(ctx context.Context, pathname string, opts vfs.Open
 	if err != nil {
 		return nil, err
 	}
-	return &vfsFile{file: fd}, nil
+	return &VFSFile{file: fd}, nil
 }
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index 89f5da3d4..16a3c18ae 100755
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
@@ -79,16 +79,22 @@ afterSymlink:
 	}
 	// Resolve any symlink at current path component.
 	if rp.ShouldFollowSymlink() && next.isSymlink() {
-		// TODO: VFS2 needs something extra for /proc/[pid]/fd/ "magic symlinks".
-		target, err := next.inode.Readlink(ctx)
+		targetVD, targetPathname, err := next.inode.Getlink(ctx)
 		if err != nil {
 			return nil, err
 		}
-		if err := rp.HandleSymlink(target); err != nil {
-			return nil, err
+		if targetVD.Ok() {
+			err := rp.HandleJump(targetVD)
+			targetVD.DecRef()
+			if err != nil {
+				return nil, err
+			}
+		} else {
+			if err := rp.HandleSymlink(targetPathname); err != nil {
+				return nil, err
+			}
 		}
 		goto afterSymlink
-
 	}
 	rp.Advance()
 	return &next.vfsd, nil
@@ -470,19 +476,25 @@ afterTrailingSymlink:
 	}
 	childDentry := childVFSD.Impl().(*Dentry)
 	childInode := childDentry.inode
-	if rp.ShouldFollowSymlink() {
-		if childDentry.isSymlink() {
-			target, err := childInode.Readlink(ctx)
+	if rp.ShouldFollowSymlink() && childDentry.isSymlink() {
+		targetVD, targetPathname, err := childInode.Getlink(ctx)
+		if err != nil {
+			return nil, err
+		}
+		if targetVD.Ok() {
+			err := rp.HandleJump(targetVD)
+			targetVD.DecRef()
 			if err != nil {
 				return nil, err
 			}
-			if err := rp.HandleSymlink(target); err != nil {
+		} else {
+			if err := rp.HandleSymlink(targetPathname); err != nil {
 				return nil, err
 			}
-			// rp.Final() may no longer be true since we now need to resolve the
-			// symlink target.
-			goto afterTrailingSymlink
 		}
+		// rp.Final() may no longer be true since we now need to resolve the
+		// symlink target.
+		goto afterTrailingSymlink
 	}
 	if err := childInode.CheckPermissions(ctx, rp.Credentials(), ats); 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 5c84b10c9..65f09af5d 100755
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
@@ -181,6 +181,11 @@ func (InodeNotSymlink) Readlink(context.Context) (string, error) {
 	return "", syserror.EINVAL
 }
 
+// Getlink implements Inode.Getlink.
+func (InodeNotSymlink) Getlink(context.Context) (vfs.VirtualDentry, string, error) {
+	return vfs.VirtualDentry{}, "", syserror.EINVAL
+}
+
 // InodeAttrs partially implements the Inode interface, specifically the
 // inodeMetadata sub interface. InodeAttrs provides functionality related to
 // inode attributes.
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index 2cefef020..ad76b9f64 100755
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -414,7 +414,21 @@ type inodeDynamicLookup interface {
 }
 
 type inodeSymlink interface {
-	// Readlink resolves the target of a symbolic link. If an inode is not a
+	// Readlink returns the target of a symbolic link. If an inode is not a
 	// symlink, the implementation should return EINVAL.
 	Readlink(ctx context.Context) (string, error)
+
+	// Getlink returns the target of a symbolic link, as used by path
+	// resolution:
+	//
+	// - If the inode is a "magic link" (a link whose target is most accurately
+	// represented as a VirtualDentry), Getlink returns (ok VirtualDentry, "",
+	// nil). A reference is taken on the returned VirtualDentry.
+	//
+	// - If the inode is an ordinary symlink, Getlink returns (zero-value
+	// VirtualDentry, symlink target, nil).
+	//
+	// - If the inode is not a symlink, Getlink returns (zero-value
+	// VirtualDentry, "", EINVAL).
+	Getlink(ctx context.Context) (vfs.VirtualDentry, string, error)
 }
diff --git a/pkg/sentry/fsimpl/kernfs/symlink.go b/pkg/sentry/fsimpl/kernfs/symlink.go
index 5918d3309..018aa503c 100755
--- a/pkg/sentry/fsimpl/kernfs/symlink.go
+++ b/pkg/sentry/fsimpl/kernfs/symlink.go
@@ -55,6 +55,11 @@ func (s *StaticSymlink) Readlink(_ context.Context) (string, error) {
 	return s.target, nil
 }
 
+// Getlink implements Inode.Getlink.
+func (s *StaticSymlink) Getlink(_ context.Context) (vfs.VirtualDentry, string, error) {
+	return vfs.VirtualDentry{}, s.target, nil
+}
+
 // SetStat implements Inode.SetStat not allowing inode attributes to be changed.
 func (*StaticSymlink) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
 	return syserror.EPERM