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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>

Documentation/filesystems/porting.rst

···
 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

···
 	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

···
 	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);
···
 {
 	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

···
 	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);
···
 	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

···
 		}
 
 		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

···
 
 	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

···
 				"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

···
 	}
 
 	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

···
 	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;
···
 	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",
···
 	}
 	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

···
 	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;
 
···
 	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);

fs/kernfs/mount.c

···
 			dput(dentry);
 			return ERR_PTR(-ENOMEM);
 		}
-		dtmp = lookup_positive_unlocked(name, dentry, strlen(name));
+		dtmp = lookup_noperm_positive_unlocked(&QSTR(name), dentry);
 		dput(dentry);
 		kfree(name);
 		if (IS_ERR(dtmp))

fs/namei.c

···
 }
 EXPORT_SYMBOL(vfs_path_lookup);
 
-static int lookup_one_common(struct mnt_idmap *idmap,
-			     const char *name, struct dentry *base, int len,
-			     struct qstr *this)
+static int lookup_noperm_common(const char *name, struct dentry *base,
+				  int len,
+				  struct qstr *this)
 {
 	this->name = name;
 	this->len = len;
···
 		if (err < 0)
 			return err;
 	}
+	return 0;
+}
 
+static int lookup_one_common(struct mnt_idmap *idmap,
+			     const char *name, struct dentry *base, int len,
+			     struct qstr *this) {
+	int err;
+	err = lookup_noperm_common(name, base, len, this);
+	if (err < 0)
+		return err;
 	return inode_permission(idmap, base->d_inode, MAY_EXEC);
 }
 
 /**
- * try_lookup_one_len - filesystem helper to lookup single pathname component
- * @name:	pathname component to lookup
+ * try_lookup_noperm - filesystem helper to lookup single pathname component
+ * @name:	qstr storing pathname component to lookup
  * @base:	base directory to lookup from
- * @len:	maximum length @len should be interpreted to
  *
  * Look up a dentry by name in the dcache, returning NULL if it does not
  * currently exist.  The function does not try to create a dentry.
  *
  * Note that this routine is purely a helper for filesystem usage and should
- * not be called by generic code.
+ * not be called by generic code.  It does no permission checking.
  *
  * No locks need be held - only a counted reference to @base is needed.
  *
  */
-struct dentry *try_lookup_one_len(const char *name, struct dentry *base, int len)
+struct dentry *try_lookup_noperm(struct qstr *name, struct dentry *base)
 {
 	struct qstr this;
 	int err;
 
-	err = lookup_one_common(&nop_mnt_idmap, name, base, len, &this);
+	err = lookup_noperm_common(name->name, base, name->len, &this);
 	if (err)
 		return ERR_PTR(err);
 
-	return lookup_dcache(&this, base, 0);
+	name->hash = this.hash;
+	return lookup_dcache(name, base, 0);
 }
-EXPORT_SYMBOL(try_lookup_one_len);
+EXPORT_SYMBOL(try_lookup_noperm);
 
 /**
- * lookup_one_len - filesystem helper to lookup single pathname component
- * @name:	pathname component to lookup
+ * lookup_noperm - filesystem helper to lookup single pathname component
+ * @name:	qstr storing pathname component to lookup
  * @base:	base directory to lookup from
- * @len:	maximum length @len should be interpreted to
  *
  * Note that this routine is purely a helper for filesystem usage and should
- * not be called by generic code.
+ * not be called by generic code.  It does no permission checking.
  *
  * The caller must hold base->i_mutex.
  */
-struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
+struct dentry *lookup_noperm(struct qstr *name, struct dentry *base)
 {
 	struct dentry *dentry;
 	struct qstr this;
···
 
 	WARN_ON_ONCE(!inode_is_locked(base->d_inode));
 
-	err = lookup_one_common(&nop_mnt_idmap, name, base, len, &this);
+	err = lookup_noperm_common(name->name, base, name->len, &this);
 	if (err)
 		return ERR_PTR(err);
 
 	dentry = lookup_dcache(&this, base, 0);
 	return dentry ? dentry : __lookup_slow(&this, base, 0);
 }
-EXPORT_SYMBOL(lookup_one_len);
+EXPORT_SYMBOL(lookup_noperm);
 
 /**
  * lookup_one - lookup single pathname component
···
  *
  * This can be used for in-kernel filesystem clients such as file servers.
  *
- * Unlike lookup_one_len, it should be called without the parent
+ * Unlike lookup_one, it should be called without the parent
  * i_rwsem held, and will take the i_rwsem itself if necessary.
  */
 struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap,
···
 EXPORT_SYMBOL(lookup_one_positive_unlocked);
 
 /**
- * lookup_one_len_unlocked - filesystem helper to lookup single pathname component
+ * lookup_noperm_unlocked - filesystem helper to lookup single pathname component
  * @name:	pathname component to lookup
  * @base:	base directory to lookup from
- * @len:	maximum length @len should be interpreted to
  *
  * Note that this routine is purely a helper for filesystem usage and should
- * not be called by generic code.
+ * not be called by generic code. It does no permission checking.
  *
- * Unlike lookup_one_len, it should be called without the parent
- * i_mutex held, and will take the i_mutex itself if necessary.
+ * Unlike lookup_noperm, it should be called without the parent
+ * i_rwsem held, and will take the i_rwsem itself if necessary.
  */
-struct dentry *lookup_one_len_unlocked(const char *name,
-				       struct dentry *base, int len)
+struct dentry *lookup_noperm_unlocked(struct qstr *name, struct dentry *base)
 {
-	return lookup_one_unlocked(&nop_mnt_idmap, &QSTR_LEN(name, len), base);
+	struct dentry *ret;
+
+	ret = try_lookup_noperm(name, base);
+	if (!ret)
+		ret = lookup_slow(name, base, 0);
+	return ret;
 }
-EXPORT_SYMBOL(lookup_one_len_unlocked);
+EXPORT_SYMBOL(lookup_noperm_unlocked);
 
 /*
- * Like lookup_one_len_unlocked(), except that it yields ERR_PTR(-ENOENT)
+ * Like lookup_noperm_unlocked(), except that it yields ERR_PTR(-ENOENT)
  * on negatives.  Returns known positive or ERR_PTR(); that's what
  * most of the users want.  Note that pinned negative with unlocked parent
- * _can_ become positive at any time, so callers of lookup_one_len_unlocked()
+ * _can_ become positive at any time, so callers of lookup_noperm_unlocked()
  * need to be very careful; pinned positives have ->d_inode stable, so
  * this one avoids such problems.
  */
-struct dentry *lookup_positive_unlocked(const char *name,
-				       struct dentry *base, int len)
+struct dentry *lookup_noperm_positive_unlocked(struct qstr *name,
+					       struct dentry *base)
 {
-	return lookup_one_positive_unlocked(&nop_mnt_idmap,
-					    &QSTR_LEN(name, len), base);
+	struct dentry *ret;
+
+	ret = lookup_noperm_unlocked(name, base);
+	if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) {
+		dput(ret);
+		ret = ERR_PTR(-ENOENT);
+	}
+	return ret;
 }
-EXPORT_SYMBOL(lookup_positive_unlocked);
+EXPORT_SYMBOL(lookup_noperm_positive_unlocked);
 
 #ifdef CONFIG_UNIX98_PTYS
 int path_pts(struct path *path)

fs/nfs/unlink.c

···
 
 	sdentry = NULL;
 	do {
-		int slen;
 		dput(sdentry);
 		sillycounter++;
-		slen = scnprintf(silly, sizeof(silly),
-				SILLYNAME_PREFIX "%0*llx%0*x",
-				SILLYNAME_FILEID_LEN, fileid,
-				SILLYNAME_COUNTER_LEN, sillycounter);
+		scnprintf(silly, sizeof(silly),
+			  SILLYNAME_PREFIX "%0*llx%0*x",
+			  SILLYNAME_FILEID_LEN, fileid,
+			  SILLYNAME_COUNTER_LEN, sillycounter);
 
 		dfprintk(VFS, "NFS: trying to rename %pd to %s\n",
 				dentry, silly);
 
-		sdentry = lookup_one_len(silly, dentry->d_parent, slen);
+		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/overlayfs/export.c

···
 	 */
 	take_dentry_name_snapshot(&name, real);
 	/*
-	 * No idmap handling here: it's an internal lookup.  Could skip
-	 * permission checking altogether, but for now just use non-idmap
-	 * transformed ids.
+	 * No idmap handling here: it's an internal lookup.
 	 */
-	this = lookup_one_len(name.name.name, connected, name.name.len);
+	this = lookup_noperm(&name.name, connected);
 	release_dentry_name_snapshot(&name);
 	err = PTR_ERR(this);
 	if (IS_ERR(this)) {

fs/overlayfs/namei.c

···
 	if (err)
 		return ERR_PTR(err);
 
-	index = lookup_positive_unlocked(name.name, ofs->workdir, name.len);
+	index = lookup_noperm_positive_unlocked(&name, ofs->workdir);
 	kfree(name.name);
 	if (IS_ERR(index)) {
 		if (PTR_ERR(index) == -ENOENT)

fs/quota/dquot.c

···
 	struct dentry *dentry;
 	int error;
 
-	dentry = lookup_positive_unlocked(qf_name, sb->s_root, strlen(qf_name));
+	dentry = lookup_noperm_positive_unlocked(&QSTR(qf_name), sb->s_root);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
 

fs/smb/client/cached_dir.c

···
 		while (*s && *s != sep)
 			s++;
 
-		child = lookup_positive_unlocked(p, dentry, s - p);
+		child = lookup_noperm_positive_unlocked(&QSTR_LEN(p, s - p),
+							dentry);
 		dput(dentry);
 		dentry = child;
 	} while (!IS_ERR(dentry));
···
 	spin_unlock(&cfids->cfid_list_lock);
 
 	/*
-	 * Skip any prefix paths in @path as lookup_positive_unlocked() ends up
+	 * Skip any prefix paths in @path as lookup_noperm_positive_unlocked() ends up
 	 * calling ->lookup() which already adds those through
 	 * build_path_from_dentry().  Also, do it earlier as we might reconnect
 	 * below when trying to send compounded request and then potentially

fs/smb/client/cifsfs.c

···
 		while (*s && *s != sep)
 			s++;
 
-		child = lookup_positive_unlocked(p, dentry, s - p);
+		child = lookup_noperm_positive_unlocked(&QSTR_LEN(p, s - p),
+							dentry);
 		dput(dentry);
 		dentry = child;
 	} while (!IS_ERR(dentry));

fs/tracefs/inode.c

···
 	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_inode(dentry)) {
 		dput(dentry);
 		dentry = ERR_PTR(-EEXIST);

fs/xfs/scrub/orphanage.c

···
 
 	/* Try to find the orphanage directory. */
 	inode_lock_nested(root_inode, I_MUTEX_PARENT);
-	orphanage_dentry = lookup_one_len(ORPHANAGE, root_dentry,
-			strlen(ORPHANAGE));
+	orphanage_dentry = lookup_noperm(&QSTR(ORPHANAGE), root_dentry);
 	if (IS_ERR(orphanage_dentry)) {
 		error = PTR_ERR(orphanage_dentry);
 		goto out_unlock_root;

include/linux/namei.h

···
 int vfs_path_lookup(struct dentry *, struct vfsmount *, const char *,
 		    unsigned int, struct path *);
 
-extern struct dentry *try_lookup_one_len(const char *, struct dentry *, int);
-extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
-extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int);
-extern struct dentry *lookup_positive_unlocked(const char *, struct dentry *, int);
+extern struct dentry *try_lookup_noperm(struct qstr *, struct dentry *);
+extern struct dentry *lookup_noperm(struct qstr *, struct dentry *);
+extern struct dentry *lookup_noperm_unlocked(struct qstr *, struct dentry *);
+extern struct dentry *lookup_noperm_positive_unlocked(struct qstr *, struct dentry *);
 struct dentry *lookup_one(struct mnt_idmap *, struct qstr *, struct dentry *);
 struct dentry *lookup_one_unlocked(struct mnt_idmap *idmap,
 				   struct qstr *name, struct dentry *base);

ipc/mqueue.c

···
 
 	ro = mnt_want_write(mnt);	/* we'll drop it in any case */
 	inode_lock(d_inode(root));
-	path.dentry = lookup_one_len(name->name, root, strlen(name->name));
+	path.dentry = lookup_noperm(&QSTR(name->name), root);
 	if (IS_ERR(path.dentry)) {
 		error = PTR_ERR(path.dentry);
 		goto out_putfd;
···
 	if (err)
 		goto out_name;
 	inode_lock_nested(d_inode(mnt->mnt_root), I_MUTEX_PARENT);
-	dentry = lookup_one_len(name->name, mnt->mnt_root,
-				strlen(name->name));
+	dentry = lookup_noperm(&QSTR(name->name), mnt->mnt_root);
 	if (IS_ERR(dentry)) {
 		err = PTR_ERR(dentry);
 		goto out_unlock;

kernel/bpf/inode.c

···
 	int ret;
 
 	inode_lock(parent->d_inode);
-	dentry = lookup_one_len(name, parent, strlen(name));
+	dentry = lookup_noperm(&QSTR(name), parent);
 	if (IS_ERR(dentry)) {
 		inode_unlock(parent->d_inode);
 		return PTR_ERR(dentry);

security/apparmor/apparmorfs.c

···
 	dir = d_inode(parent);
 
 	inode_lock(dir);
-	dentry = lookup_one_len(name, parent, strlen(name));
+	dentry = lookup_noperm(&QSTR(name), parent);
 	if (IS_ERR(dentry)) {
 		error = PTR_ERR(dentry);
 		goto fail_lock;
···
 		return error;
 
 	inode_lock(d_inode(parent));
-	dentry = lookup_one_len(NULL_FILE_NAME, parent, strlen(NULL_FILE_NAME));
+	dentry = lookup_noperm(&QSTR(NULL_FILE_NAME), parent);
 	if (IS_ERR(dentry)) {
 		error = PTR_ERR(dentry);
 		goto out;

security/inode.c

···
 	dir = d_inode(parent);
 
 	inode_lock(dir);
-	dentry = lookup_one_len(name, parent, strlen(name));
+	dentry = lookup_noperm(&QSTR(name), parent);
 	if (IS_ERR(dentry))
 		goto out;