VFS: rename lookup_one_len family to lookup_noperm and remove permission check

The lookup_one_len family of functions is (now) only used internally by
a filesystem on itself either
- in a context where permission checking is irrelevant such as by a
  virtual filesystem populating itself, or xfs accessing its ORPHANAGE
  or dquota accessing the quota file; or
- in a context where a permission check (MAY_EXEC on the parent) has just
  been performed such as a network filesystem finding in "silly-rename"
  file in the same directory.  This is also the context after the
  _parentat() functions where currently lookup_one_qstr_excl() is used.

So the permission check is pointless.

The name "one_len" is unhelpful in understanding the purpose of these
functions and should be changed.  Most of the callers pass the len as
"strlen()" so using a qstr and QSTR() can simplify the code.

This patch renames these functions (include lookup_positive_unlocked()
which is part of the family despite the name) to have a name based on
"lookup_noperm".  They are changed to receive a 'struct qstr' instead
of separate name and len.  In a few cases the use of QSTR() results in a
new call to strlen().

try_lookup_noperm() takes a pointer to a qstr instead of the whole
qstr.  This is consistent with d_hash_and_lookup() (which is nearly
identical) and useful for lookup_noperm_unlocked().

The new lookup_noperm_common() doesn't take a qstr yet.  That will be
tidied up in a subsequent patch.

Signed-off-by: NeilBrown <neil@brown.name>
Link: https://lore.kernel.org/r/20250319031545.2999807-5-neil@brown.name
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: neilbrown

Documentation/filesystems/porting.rst

@@ -1212,3 +1212,23 @@ lookup_one(), lookup_one_unlocked(), lookup_one_positive_unlocked() now
 take a qstr instead of a name and len.  These, not the "one_len"
 versions, should be used whenever accessing a filesystem from outside
 that filesysmtem, through a mount point - which will have a mnt_idmap.
+
+---
+
+** mandatory**
+
+Functions try_lookup_one_len(), lookup_one_len(),
+lookup_one_len_unlocked() and lookup_positive_unlocked() have been
+renamed to try_lookup_noperm(), lookup_noperm(),
+lookup_noperm_unlocked(), lookup_noperm_positive_unlocked().  They now
+take a qstr instead of separate name and length.  QSTR() can be used
+when strlen() is needed for the length.
+
+For try_lookup_noperm() a reference to the qstr is passed in case the
+hash might subsequently be needed.
+
+These function no longer do any permission checking - they previously
+checked that the caller has 'X' permission on the parent.  They must
+ONLY be used internally by a filesystem on itself when it knows that
+permissions are irrelevant or in a context where permission checks have
+already been performed such as after vfs_path_parent_lookup()

arch/s390/hypfs/inode.c

@@ -342,7 +342,7 @@ static struct dentry *hypfs_create_file(struct dentry *parent, const char *name,
 	struct inode *inode;
 
 	inode_lock(d_inode(parent));
-	dentry = lookup_one_len(name, parent, strlen(name));
+	dentry = lookup_noperm(&QSTR(name), parent);
 	if (IS_ERR(dentry)) {
 		dentry = ERR_PTR(-ENOMEM);
 		goto fail;

drivers/android/binderfs.c

@@ -187,7 +187,7 @@ static int binderfs_binder_device_create(struct inode *ref_inode,
 	inode_lock(d_inode(root));
 
 	/* look it up */
-	dentry = lookup_one_len(name, root, name_len);
+	dentry = lookup_noperm(&QSTR(name), root);
 	if (IS_ERR(dentry)) {
 		inode_unlock(d_inode(root));
 		ret = PTR_ERR(dentry);
@@ -487,7 +487,7 @@ static struct dentry *binderfs_create_dentry(struct dentry *parent,
 {
 	struct dentry *dentry;
 
-	dentry = lookup_one_len(name, parent, strlen(name));
+	dentry = lookup_noperm(&QSTR(name), parent);
 	if (IS_ERR(dentry))
 		return dentry;
 

drivers/infiniband/hw/qib/qib_fs.c

@@ -90,7 +90,7 @@ static int create_file(const char *name, umode_t mode,
 	int error;
 
 	inode_lock(d_inode(parent));
-	*dentry = lookup_one_len(name, parent, strlen(name));
+	*dentry = lookup_noperm(&QSTR(name), parent);
 	if (!IS_ERR(*dentry))
 		error = qibfs_mknod(d_inode(parent), *dentry,
 				    mode, fops, data);
@@ -433,7 +433,7 @@ static int remove_device_files(struct super_block *sb,
 	char unit[10];
 
 	snprintf(unit, sizeof(unit), "%u", dd->unit);
-	dir = lookup_one_len_unlocked(unit, sb->s_root, strlen(unit));
+	dir = lookup_noperm_unlocked(&QSTR(unit), sb->s_root);
 
 	if (IS_ERR(dir)) {
 		pr_err("Lookup of %s failed\n", unit);

fs/afs/dir.c

@@ -943,7 +943,7 @@ static struct dentry *afs_lookup_atsys(struct inode *dir, struct dentry *dentry)
 		}
 
 		strcpy(p, name);
-		ret = lookup_one_len(buf, dentry->d_parent, len);
+		ret = lookup_noperm(&QSTR(buf), dentry->d_parent);
 		if (IS_ERR(ret) || d_is_positive(ret))
 			goto out_s;
 		dput(ret);

fs/afs/dir_silly.c

@@ -113,16 +113,14 @@ int afs_sillyrename(struct afs_vnode *dvnode, struct afs_vnode *vnode,
 
 	sdentry = NULL;
 	do {
-		int slen;
-
 		dput(sdentry);
 		sillycounter++;
 
 		/* Create a silly name.  Note that the ".__afs" prefix is
 		 * understood by the salvager and must not be changed.
 		 */
-		slen = scnprintf(silly, sizeof(silly), ".__afs%04X", sillycounter);
-		sdentry = lookup_one_len(silly, dentry->d_parent, slen);
+		scnprintf(silly, sizeof(silly), ".__afs%04X", sillycounter);
+		sdentry = lookup_noperm(&QSTR(silly), dentry->d_parent);
 
 		/* N.B. Better to return EBUSY here ... it could be dangerous
 		 * to delete the file while it's in use.

fs/autofs/dev-ioctl.c

@@ -459,7 +459,8 @@ static int autofs_dev_ioctl_timeout(struct file *fp,
 				"the parent autofs mount timeout which could "
 				"prevent shutdown\n");
 
-		dentry = try_lookup_one_len(param->path, base, path_len);
+		dentry = try_lookup_noperm(&QSTR_LEN(param->path, path_len),
+					   base);
 		if (IS_ERR_OR_NULL(dentry))
 			return dentry ? PTR_ERR(dentry) : -ENOENT;
 		ino = autofs_dentry_ino(dentry);

fs/binfmt_misc.c

@@ -842,7 +842,7 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 	}
 
 	inode_lock(d_inode(root));
-	dentry = lookup_one_len(e->name, root, strlen(e->name));
+	dentry = lookup_noperm(&QSTR(e->name), root);
 	err = PTR_ERR(dentry);
 	if (IS_ERR(dentry))
 		goto out;

fs/debugfs/inode.c

@@ -346,7 +346,7 @@ struct dentry *debugfs_lookup(const char *name, struct dentry *parent)
 	if (!parent)
 		parent = debugfs_mount->mnt_root;
 
-	dentry = lookup_positive_unlocked(name, parent, strlen(name));
+	dentry = lookup_noperm_positive_unlocked(&QSTR(name), parent);
 	if (IS_ERR(dentry))
 		return NULL;
 	return dentry;
@@ -388,7 +388,7 @@ static struct dentry *start_creating(const char *name, struct dentry *parent)
 	if (unlikely(IS_DEADDIR(d_inode(parent))))
 		dentry = ERR_PTR(-ENOENT);
 	else
-		dentry = lookup_one_len(name, parent, strlen(name));
+		dentry = lookup_noperm(&QSTR(name), parent);
 	if (!IS_ERR(dentry) && d_really_is_positive(dentry)) {
 		if (d_is_dir(dentry))
 			pr_err("Directory '%s' with parent '%s' already present!\n",
@@ -872,7 +872,7 @@ int __printf(2, 3) debugfs_change_name(struct dentry *dentry, const char *fmt, .
 	}
 	if (strcmp(old_name.name.name, new_name) == 0)
 		goto out;
-	target = lookup_one_len(new_name, parent, strlen(new_name));
+	target = lookup_noperm(&QSTR(new_name), parent);
 	if (IS_ERR(target)) {
 		error = PTR_ERR(target);
 		goto out;

fs/ecryptfs/inode.c

@@ -394,8 +394,8 @@ static struct dentry *ecryptfs_lookup(struct inode *ecryptfs_dir_inode,
 	char *encrypted_and_encoded_name = NULL;
 	struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
 	struct dentry *lower_dir_dentry, *lower_dentry;
-	const char *name = ecryptfs_dentry->d_name.name;
-	size_t len = ecryptfs_dentry->d_name.len;
+	struct qstr qname = QSTR_INIT(ecryptfs_dentry->d_name.name,
+				      ecryptfs_dentry->d_name.len);
 	struct dentry *res;
 	int rc = 0;
 
@@ -404,23 +404,25 @@ static struct dentry *ecryptfs_lookup(struct inode *ecryptfs_dir_inode,
 	mount_crypt_stat = &ecryptfs_superblock_to_private(
 				ecryptfs_dentry->d_sb)->mount_crypt_stat;
 	if (mount_crypt_stat->flags & ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES) {
+		size_t len = qname.len;
 		rc = ecryptfs_encrypt_and_encode_filename(
 			&encrypted_and_encoded_name, &len,
-			mount_crypt_stat, name, len);
+			mount_crypt_stat, qname.name, len);
 		if (rc) {
 			printk(KERN_ERR "%s: Error attempting to encrypt and encode "
 			       "filename; rc = [%d]\n", __func__, rc);
 			return ERR_PTR(rc);
 		}
-		name = encrypted_and_encoded_name;
+		qname.name = encrypted_and_encoded_name;
+		qname.len = len;
 	}
 
-	lower_dentry = lookup_one_len_unlocked(name, lower_dir_dentry, len);
+	lower_dentry = lookup_noperm_unlocked(&qname, lower_dir_dentry);
 	if (IS_ERR(lower_dentry)) {
-		ecryptfs_printk(KERN_DEBUG, "%s: lookup_one_len() returned "
+		ecryptfs_printk(KERN_DEBUG, "%s: lookup_noperm() returned "
 				"[%ld] on lower_dentry = [%s]\n", __func__,
 				PTR_ERR(lower_dentry),
-				name);
+				qname.name);
 		res = ERR_CAST(lower_dentry);
 	} else {
 		res = ecryptfs_lookup_interpose(ecryptfs_dentry, lower_dentry);