From: Andreas Gruenbacher <agruen@suse.de>
Subject: Add d_namespace_path() to compute namespace relative pathnames

In AppArmor, we are interested in pathnames relative to the namespace root.
This is the same as d_path() except for the root where the search ends. Add
a function for computing the namespace-relative path.

Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Signed-off-by: John Johansen <jjohansen@suse.de>

---
 fs/dcache.c            |    6 +++---
 fs/namespace.c         |   27 +++++++++++++++++++++++++++
 include/linux/dcache.h |    3 ++-
 include/linux/mount.h  |    2 ++
 4 files changed, 34 insertions(+), 4 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1766,9 +1766,9 @@ shouldnt_be_hashed:
  *
  * Returns the buffer or an error code.
  */
-static char *__d_path(struct dentry *dentry, struct vfsmount *vfsmnt,
-		       struct path *root, char *buffer, int buflen,
-		       int fail_deleted)
+char *__d_path(struct dentry *dentry, struct vfsmount *vfsmnt,
+	       struct path *root, char *buffer, int buflen,
+	       int fail_deleted)
 {
 	int namelen, is_slash, vfsmount_locked = 0;
 
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1852,3 +1852,30 @@ void __put_mnt_ns(struct mnt_namespace *
 	release_mounts(&umount_list);
 	kfree(ns);
 }
+
+char *d_namespace_path(struct dentry *dentry, struct vfsmount *vfsmnt,
+		       char *buf, int buflen)
+{
+	struct path root, ns_root = { };
+	char *res;
+
+	read_lock(&current->fs->lock);
+	root = current->fs->root;
+	path_get(&current->fs->root);
+	read_unlock(&current->fs->lock);
+	spin_lock(&vfsmount_lock);
+	if (root.mnt)
+		ns_root.mnt = mntget(root.mnt->mnt_ns->root);
+	if (ns_root.mnt)
+		ns_root.dentry = dget(ns_root.mnt->mnt_root);
+	spin_unlock(&vfsmount_lock);
+	res = __d_path(dentry, vfsmnt, &ns_root, buf, buflen, 1);
+	path_put(&root);
+	path_put(&ns_root);
+
+	/* Prevent empty path for lazily unmounted filesystems. */
+	if (!IS_ERR(res) && *res == '\0')
+		*--res = '.';
+	return res;
+}
+EXPORT_SYMBOL(d_namespace_path);
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -300,7 +300,8 @@ extern int d_validate(struct dentry *, s
  * helper function for dentry_operations.d_dname() members
  */
 extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
-
+extern char *__d_path(struct dentry *, struct vfsmount *, struct path *,
+		      char *, int, int);
 extern char *d_path(struct path *, char *, int);
 
 /* Allocation counts.. */
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -103,5 +103,7 @@ extern void mark_mounts_for_expiry(struc
 extern spinlock_t vfsmount_lock;
 extern dev_t name_to_dev_t(char *name);
 
+extern char *d_namespace_path(struct dentry *, struct vfsmount *, char *, int);
+
 #endif
 #endif /* _LINUX_MOUNT_H */