Support listxattr and removexattr syscalls.

Note that these are only implemented for tmpfs, and other impls will still
return EOPNOTSUPP.

PiperOrigin-RevId: 293899385

8 files changed, 87 insertions, 16 deletions

diff --git a/pkg/sentry/fs/copy_up.go b/pkg/sentry/fs/copy_up.go
index f6c79e51b..b060a12ff 100644
--- a/pkg/sentry/fs/copy_up.go
+++ b/pkg/sentry/fs/copy_up.go
@@ -401,7 +401,7 @@ func copyAttributesLocked(ctx context.Context, upper *Inode, lower *Inode) error
 	if err != nil {
 		return err
 	}
-	lowerXattr, err := lower.ListXattr(ctx)
+	lowerXattr, err := lower.ListXattr(ctx, linux.XATTR_SIZE_MAX)
 	if err != nil && err != syserror.EOPNOTSUPP {
 		return err
 	}
diff --git a/pkg/sentry/fs/fsutil/inode.go b/pkg/sentry/fs/fsutil/inode.go
index 252830572..daecc4ffe 100644
--- a/pkg/sentry/fs/fsutil/inode.go
+++ b/pkg/sentry/fs/fsutil/inode.go
@@ -247,7 +247,7 @@ func (i *InodeSimpleExtendedAttributes) SetXattr(_ context.Context, _ *fs.Inode,
 }
 
 // ListXattr implements fs.InodeOperations.ListXattr.
-func (i *InodeSimpleExtendedAttributes) ListXattr(context.Context, *fs.Inode) (map[string]struct{}, error) {
+func (i *InodeSimpleExtendedAttributes) ListXattr(context.Context, *fs.Inode, uint64) (map[string]struct{}, error) {
 	i.mu.RLock()
 	names := make(map[string]struct{}, len(i.xattrs))
 	for name := range i.xattrs {
@@ -257,6 +257,17 @@ func (i *InodeSimpleExtendedAttributes) ListXattr(context.Context, *fs.Inode) (m
 	return names, nil
 }
 
+// RemoveXattr implements fs.InodeOperations.RemoveXattr.
+func (i *InodeSimpleExtendedAttributes) RemoveXattr(_ context.Context, _ *fs.Inode, name string) error {
+	i.mu.RLock()
+	defer i.mu.RUnlock()
+	if _, ok := i.xattrs[name]; ok {
+		delete(i.xattrs, name)
+		return nil
+	}
+	return syserror.ENOATTR
+}
+
 // staticFile is a file with static contents. It is returned by
 // InodeStaticFileGetter.GetFile.
 //
@@ -460,10 +471,15 @@ func (InodeNoExtendedAttributes) SetXattr(context.Context, *fs.Inode, string, st
 }
 
 // ListXattr implements fs.InodeOperations.ListXattr.
-func (InodeNoExtendedAttributes) ListXattr(context.Context, *fs.Inode) (map[string]struct{}, error) {
+func (InodeNoExtendedAttributes) ListXattr(context.Context, *fs.Inode, uint64) (map[string]struct{}, error) {
 	return nil, syserror.EOPNOTSUPP
 }
 
+// RemoveXattr implements fs.InodeOperations.RemoveXattr.
+func (InodeNoExtendedAttributes) RemoveXattr(context.Context, *fs.Inode, string) error {
+	return syserror.EOPNOTSUPP
+}
+
 // InodeNoopRelease implements fs.InodeOperations.Release as a noop.
 type InodeNoopRelease struct{}
 
diff --git a/pkg/sentry/fs/gofer/context_file.go b/pkg/sentry/fs/gofer/context_file.go
index 3da818aed..125907d70 100644
--- a/pkg/sentry/fs/gofer/context_file.go
+++ b/pkg/sentry/fs/gofer/context_file.go
@@ -73,6 +73,20 @@ func (c *contextFile) setXattr(ctx context.Context, name, value string, flags ui
 	return err
 }
 
+func (c *contextFile) listXattr(ctx context.Context, size uint64) (map[string]struct{}, error) {
+	ctx.UninterruptibleSleepStart(false)
+	xattrs, err := c.file.ListXattr(size)
+	ctx.UninterruptibleSleepFinish(false)
+	return xattrs, err
+}
+
+func (c *contextFile) removeXattr(ctx context.Context, name string) error {
+	ctx.UninterruptibleSleepStart(false)
+	err := c.file.RemoveXattr(name)
+	ctx.UninterruptibleSleepFinish(false)
+	return err
+}
+
 func (c *contextFile) allocate(ctx context.Context, mode p9.AllocateMode, offset, length uint64) error {
 	ctx.UninterruptibleSleepStart(false)
 	err := c.file.Allocate(mode, offset, length)
diff --git a/pkg/sentry/fs/gofer/inode.go b/pkg/sentry/fs/gofer/inode.go
index ac28174d2..1c934981b 100644
--- a/pkg/sentry/fs/gofer/inode.go
+++ b/pkg/sentry/fs/gofer/inode.go
@@ -604,18 +604,23 @@ func (i *inodeOperations) Truncate(ctx context.Context, inode *fs.Inode, length
 }
 
 // GetXattr implements fs.InodeOperations.GetXattr.
-func (i *inodeOperations) GetXattr(ctx context.Context, inode *fs.Inode, name string, size uint64) (string, error) {
+func (i *inodeOperations) GetXattr(ctx context.Context, _ *fs.Inode, name string, size uint64) (string, error) {
 	return i.fileState.file.getXattr(ctx, name, size)
 }
 
 // SetXattr implements fs.InodeOperations.SetXattr.
-func (i *inodeOperations) SetXattr(ctx context.Context, inode *fs.Inode, name string, value string, flags uint32) error {
+func (i *inodeOperations) SetXattr(ctx context.Context, _ *fs.Inode, name string, value string, flags uint32) error {
 	return i.fileState.file.setXattr(ctx, name, value, flags)
 }
 
 // ListXattr implements fs.InodeOperations.ListXattr.
-func (i *inodeOperations) ListXattr(context.Context, *fs.Inode) (map[string]struct{}, error) {
-	return nil, syscall.EOPNOTSUPP
+func (i *inodeOperations) ListXattr(ctx context.Context, _ *fs.Inode, size uint64) (map[string]struct{}, error) {
+	return i.fileState.file.listXattr(ctx, size)
+}
+
+// RemoveXattr implements fs.InodeOperations.RemoveXattr.
+func (i *inodeOperations) RemoveXattr(ctx context.Context, _ *fs.Inode, name string) error {
+	return i.fileState.file.removeXattr(ctx, name)
 }
 
 // Allocate implements fs.InodeOperations.Allocate.
diff --git a/pkg/sentry/fs/inode.go b/pkg/sentry/fs/inode.go
index b66c091ab..55fb71c16 100644
--- a/pkg/sentry/fs/inode.go
+++ b/pkg/sentry/fs/inode.go
@@ -278,11 +278,19 @@ func (i *Inode) SetXattr(ctx context.Context, d *Dirent, name, value string, fla
 }
 
 // ListXattr calls i.InodeOperations.ListXattr with i as the Inode.
-func (i *Inode) ListXattr(ctx context.Context) (map[string]struct{}, error) {
+func (i *Inode) ListXattr(ctx context.Context, size uint64) (map[string]struct{}, error) {
 	if i.overlay != nil {
-		return overlayListXattr(ctx, i.overlay)
+		return overlayListXattr(ctx, i.overlay, size)
 	}
-	return i.InodeOperations.ListXattr(ctx, i)
+	return i.InodeOperations.ListXattr(ctx, i, size)
+}
+
+// RemoveXattr calls i.InodeOperations.RemoveXattr with i as the Inode.
+func (i *Inode) RemoveXattr(ctx context.Context, d *Dirent, name string) error {
+	if i.overlay != nil {
+		return overlayRemoveXattr(ctx, i.overlay, d, name)
+	}
+	return i.InodeOperations.RemoveXattr(ctx, i, name)
 }
 
 // CheckPermission will check if the caller may access this file in the
diff --git a/pkg/sentry/fs/inode_operations.go b/pkg/sentry/fs/inode_operations.go
index 70f2eae96..2bbfb72ef 100644
--- a/pkg/sentry/fs/inode_operations.go
+++ b/pkg/sentry/fs/inode_operations.go
@@ -190,7 +190,18 @@ type InodeOperations interface {
 	// ListXattr returns the set of all extended attributes names that
 	// have values. Inodes that do not support extended attributes return
 	// EOPNOTSUPP.
-	ListXattr(ctx context.Context, inode *Inode) (map[string]struct{}, error)
+	//
+	// If this is called through the listxattr(2) syscall, size indicates the
+	// size of the buffer that the application has allocated to hold the
+	// attribute list. If the list would be larger than size, implementations may
+	// return ERANGE to indicate that the buffer is too small, but they are also
+	// free to ignore the hint entirely. All size checking is done independently
+	// at the syscall layer.
+	ListXattr(ctx context.Context, inode *Inode, size uint64) (map[string]struct{}, error)
+
+	// RemoveXattr removes an extended attribute specified by name. Inodes that
+	// do not support extended attributes return EOPNOTSUPP.
+	RemoveXattr(ctx context.Context, inode *Inode, name string) error
 
 	// Check determines whether an Inode can be accessed with the
 	// requested permission mask using the context (which gives access
diff --git a/pkg/sentry/fs/inode_overlay.go b/pkg/sentry/fs/inode_overlay.go
index 4729b4aac..5ada33a32 100644
--- a/pkg/sentry/fs/inode_overlay.go
+++ b/pkg/sentry/fs/inode_overlay.go
@@ -564,15 +564,15 @@ func overlaySetxattr(ctx context.Context, o *overlayEntry, d *Dirent, name, valu
 	return o.upper.SetXattr(ctx, d, name, value, flags)
 }
 
-func overlayListXattr(ctx context.Context, o *overlayEntry) (map[string]struct{}, error) {
+func overlayListXattr(ctx context.Context, o *overlayEntry, size uint64) (map[string]struct{}, error) {
 	o.copyMu.RLock()
 	defer o.copyMu.RUnlock()
 	var names map[string]struct{}
 	var err error
 	if o.upper != nil {
-		names, err = o.upper.ListXattr(ctx)
+		names, err = o.upper.ListXattr(ctx, size)
 	} else {
-		names, err = o.lower.ListXattr(ctx)
+		names, err = o.lower.ListXattr(ctx, size)
 	}
 	for name := range names {
 		// Same as overlayGetXattr, we shouldn't forward along
@@ -584,6 +584,18 @@ func overlayListXattr(ctx context.Context, o *overlayEntry) (map[string]struct{}
 	return names, err
 }
 
+func overlayRemoveXattr(ctx context.Context, o *overlayEntry, d *Dirent, name string) error {
+	// Don't allow changes to overlay xattrs through a removexattr syscall.
+	if strings.HasPrefix(XattrOverlayPrefix, name) {
+		return syserror.EPERM
+	}
+
+	if err := copyUp(ctx, d); err != nil {
+		return err
+	}
+	return o.upper.RemoveXattr(ctx, d, name)
+}
+
 func overlayCheck(ctx context.Context, o *overlayEntry, p PermMask) error {
 	o.copyMu.RLock()
 	// Hot path. Avoid defers.
diff --git a/pkg/sentry/fs/tmpfs/tmpfs.go b/pkg/sentry/fs/tmpfs/tmpfs.go
index c00cef0a5..3c2b583ae 100644
--- a/pkg/sentry/fs/tmpfs/tmpfs.go
+++ b/pkg/sentry/fs/tmpfs/tmpfs.go
@@ -159,8 +159,13 @@ func (d *Dir) SetXattr(ctx context.Context, i *fs.Inode, name, value string, fla
 }
 
 // ListXattr implements fs.InodeOperations.ListXattr.
-func (d *Dir) ListXattr(ctx context.Context, i *fs.Inode) (map[string]struct{}, error) {
-	return d.ramfsDir.ListXattr(ctx, i)
+func (d *Dir) ListXattr(ctx context.Context, i *fs.Inode, size uint64) (map[string]struct{}, error) {
+	return d.ramfsDir.ListXattr(ctx, i, size)
+}
+
+// RemoveXattr implements fs.InodeOperations.RemoveXattr.
+func (d *Dir) RemoveXattr(ctx context.Context, i *fs.Inode, name string) error {
+	return d.ramfsDir.RemoveXattr(ctx, i, name)
 }
 
 // Lookup implements fs.InodeOperations.Lookup.