[AppArmor 31/47] 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 <[email protected]>
Signed-off-by: John Johansen <[email protected]>

---
 fs/dcache.c            |    4 ++--
 fs/namespace.c         |   26 ++++++++++++++++++++++++++
 include/linux/dcache.h |    1 +
 include/linux/mount.h  |    3 +++
 4 files changed, 32 insertions(+), 2 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1763,8 +1763,8 @@ shouldnt_be_hashed:
  *
  * Returns the buffer or an error code.
  */
-static char *__d_path(struct path *path, struct path *root,
-                     char *buffer, int buflen, int fail_deleted)
+char *__d_path(struct path *path, struct path *root, char *buffer, int buflen,
+	       int fail_deleted)
 {
     int namelen, is_slash, vfsmount_locked = 0;
 	struct dentry *dentry = path->dentry;
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -26,6 +26,7 @@
 #include <linux/security.h>
 #include <linux/mount.h>
 #include <linux/ramfs.h>
+#include <linux/path.h>
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
 #include "pnode.h"
@@ -2167,3 +2168,28 @@ void __put_mnt_ns(struct mnt_namespace *
 	release_mounts(&umount_list);
 	kfree(ns);
 }
+
+char *d_namespace_path(struct path *path, char *buf, int buflen)
+{
+	struct path root = { NULL, NULL };
+	struct vfsmount *rootmnt;
+	char *res;
+
+	read_lock(&current->fs->lock);
+	rootmnt = mntget(current->fs->root.mnt);
+	read_unlock(&current->fs->lock);
+	spin_lock(&vfsmount_lock);
+	if (rootmnt->mnt_ns)
+		root.mnt = mntget(rootmnt->mnt_ns->root);
+	spin_unlock(&vfsmount_lock);
+	mntput(rootmnt);
+	if (root.mnt)
+		root.dentry = dget(root.mnt->mnt_root);
+	res = __d_path(path, &root, buf, buflen, 1);
+	path_put(&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
@@ -302,6 +302,7 @@ extern int d_validate(struct dentry *, s
 extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
 
 extern char *d_path(struct path *, char *, int);
+extern char *__d_path(struct path *, struct path *, char *, int, int);
 
 /* Allocation counts.. */
 
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -16,6 +16,7 @@
 #include <linux/list.h>
 #include <linux/nodemask.h>
 #include <linux/spinlock.h>
+#include <linux/path.h>
 #include <asm/atomic.h>
 
 struct super_block;
@@ -114,5 +115,7 @@ extern void shrink_submounts(struct vfsm
 extern spinlock_t vfsmount_lock;
 extern dev_t name_to_dev_t(char *name);
 
+extern char *d_namespace_path(struct path *, char *, int);
+
 #endif
 #endif /* _LINUX_MOUNT_H */

-- 

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---

• References:
  • [AppArmor 00/47] AppArmor security module overview
    • From: [email protected], [email protected]

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