From 733d013f979a2107fd866ff3c05249c3e8ba5102 Mon Sep 17 00:00:00 2001
From: Boyuan He <heboyuan@google.com>
Date: Tue, 18 Aug 2020 23:50:22 +0000
Subject: Implement FUSE_READLINK

Fixes #3316
---
 pkg/sentry/fsimpl/fuse/fusefs.go | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

(limited to 'pkg/sentry/fsimpl/fuse')

diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index 0021e2933..8db337a2e 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -225,6 +225,9 @@ type inode struct {
 
 	// version of the inode.
 	version uint64
+
+	// link is result of following a symbolic link.
+	link string
 }
 
 func (fs *filesystem) newRootInode(creds *auth.Credentials, mode linux.FileMode) *kernfs.Dentry {
@@ -406,6 +409,33 @@ func (i *inode) newEntry(ctx context.Context, name string, fileType linux.FileMo
 	return child.VFSDentry(), nil
 }
 
+// Readlink implements kernfs.Inode.Readlink.
+func (i *inode) Readlink(ctx context.Context, mnt *vfs.Mount) (string, error) {
+	if i.Mode().FileType()&linux.S_IFLNK == 0 {
+		return "", syserror.EINVAL
+	}
+	if i.link == "" {
+		kernelTask := kernel.TaskFromContext(ctx)
+		if kernelTask == nil {
+			log.Warningf("fusefs.Inode.Readlink: couldn't get kernel task from context")
+			return "", syserror.EINVAL
+		}
+		req, err := i.fs.conn.NewRequest(auth.CredentialsFromContext(ctx), uint32(kernelTask.ThreadID()), i.NodeID, linux.FUSE_READLINK, &linux.FUSEEmptyIn{})
+		if err != nil {
+			return "", err
+		}
+		res, err := i.fs.conn.Call(kernelTask, req)
+		if err != nil {
+			return "", err
+		}
+		i.link = string(res.data[res.hdr.SizeBytes():])
+		if !mnt.Options().ReadOnly {
+			i.attributeTime = 0
+		}
+	}
+	return i.link, nil
+}
+
 // statFromFUSEAttr makes attributes from linux.FUSEAttr to linux.Statx. The
 // opts.Sync attribute is ignored since the synchronization is handled by the
 // FUSE server.
-- 
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