smb/server: add ksmbd_vfs_kern_path()

The function ksmbd_vfs_kern_path_locked() seems to serve two functions
and as a result has an odd interface.

On success it returns with the parent directory locked and with write
access on that filesystem requested, but it may have crossed over a
mount point to return the path, which makes the lock and the write
access irrelevant.

This patches separates the functionality into two functions:
- ksmbd_vfs_kern_path() does not lock the parent, does not request
  write access, but does cross mount points
- ksmbd_vfs_kern_path_locked() does not cross mount points but
  does lock the parent and request write access.

The parent_path parameter is no longer needed.  For the _locked case
the final path is sufficient to drop write access and to unlock the
parent (using path->dentry->d_parent which is safe while the lock is
held).

There were 3 caller of ksmbd_vfs_kern_path_locked().

- smb2_create_link() needs to remove the target if it existed and
  needs the lock and the write-access, so it continues to use
  ksmbd_vfs_kern_path_locked().  It would not make sense to
  cross mount points in this case.
- smb2_open() is the only user that needs to cross mount points
  and it has no need for the lock or write access, so it now uses
  ksmbd_vfs_kern_path()
- smb2_creat() does not need to cross mountpoints as it is accessing
  a file that it has just created on *this* filesystem.  But also it
  does not need the lock or write access because by the time
  ksmbd_vfs_kern_path_locked() was called it has already created the
  file.  So it could use either interface.  It is simplest to use
  ksmbd_vfs_kern_path().

ksmbd_vfs_kern_path_unlock() is still needed after
ksmbd_vfs_kern_path_locked() but it doesn't require the parent_path any
more.  After a successful call to ksmbd_vfs_kern_path(), only path_put()
is needed to release the path.

Signed-off-by: NeilBrown <neil@brown.name>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/server/smb2pdu.c

@@ -2581,7 +2581,7 @@ static void smb2_update_xattrs(struct ksmbd_tree_connect *tcon,
 	}
 }
 
-static int smb2_creat(struct ksmbd_work *work, struct path *parent_path,
+static int smb2_creat(struct ksmbd_work *work,
 		      struct path *path, char *name, int open_flags,
 		      umode_t posix_mode, bool is_dir)
 {
@@ -2610,7 +2610,7 @@ static int smb2_creat(struct ksmbd_work *work, struct path *parent_path,
 			return rc;
 	}
 
-	rc = ksmbd_vfs_kern_path_locked(work, name, 0, parent_path, path, 0);
+	rc = ksmbd_vfs_kern_path(work, name, 0, path, 0);
 	if (rc) {
 		pr_err("cannot get linux path (%s), err = %d\n",
 		       name, rc);
@@ -2860,7 +2860,7 @@ int smb2_open(struct ksmbd_work *work)
 	struct ksmbd_tree_connect *tcon = work->tcon;
 	struct smb2_create_req *req;
 	struct smb2_create_rsp *rsp;
-	struct path path, parent_path;
+	struct path path;
 	struct ksmbd_share_config *share = tcon->share_conf;
 	struct ksmbd_file *fp = NULL;
 	struct file *filp = NULL;
@@ -3116,8 +3116,8 @@ int smb2_open(struct ksmbd_work *work)
 		goto err_out2;
 	}
 
-	rc = ksmbd_vfs_kern_path_locked(work, name, LOOKUP_NO_SYMLINKS,
-					&parent_path, &path, 1);
+	rc = ksmbd_vfs_kern_path(work, name, LOOKUP_NO_SYMLINKS,
+				 &path, 1);
 	if (!rc) {
 		file_present = true;
 
@@ -3238,7 +3238,7 @@ int smb2_open(struct ksmbd_work *work)
 
 	/*create file if not present */
 	if (!file_present) {
-		rc = smb2_creat(work, &parent_path, &path, name, open_flags,
+		rc = smb2_creat(work, &path, name, open_flags,
 				posix_mode,
 				req->CreateOptions & FILE_DIRECTORY_FILE_LE);
 		if (rc) {
@@ -3443,7 +3443,7 @@ int smb2_open(struct ksmbd_work *work)
 	}
 
 	if (file_present || created)
-		ksmbd_vfs_kern_path_unlock(&parent_path, &path);
+		path_put(&path);
 
 	if (!S_ISDIR(file_inode(filp)->i_mode) && open_flags & O_TRUNC &&
 	    !fp->attrib_only && !stream_name) {
@@ -3724,7 +3724,7 @@ int smb2_open(struct ksmbd_work *work)
 
 err_out:
 	if (rc && (file_present || created))
-		ksmbd_vfs_kern_path_unlock(&parent_path, &path);
+		path_put(&path);
 
 err_out1:
 	ksmbd_revert_fsids(work);
@@ -6036,7 +6036,7 @@ static int smb2_create_link(struct ksmbd_work *work,
 			    struct nls_table *local_nls)
 {
 	char *link_name = NULL, *target_name = NULL, *pathname = NULL;
-	struct path path, parent_path;
+	struct path path;
 	int rc;
 
 	if (buf_len < (u64)sizeof(struct smb2_file_link_info) +
@@ -6065,7 +6065,7 @@ static int smb2_create_link(struct ksmbd_work *work,
 
 	ksmbd_debug(SMB, "target name is %s\n", target_name);
 	rc = ksmbd_vfs_kern_path_locked(work, link_name, LOOKUP_NO_SYMLINKS,
-					&parent_path, &path, 0);
+					&path, 0);
 	if (rc) {
 		if (rc != -ENOENT)
 			goto out;
@@ -6083,7 +6083,7 @@ static int smb2_create_link(struct ksmbd_work *work,
 			ksmbd_debug(SMB, "link already exists\n");
 			goto out;
 		}
-		ksmbd_vfs_kern_path_unlock(&parent_path, &path);
+		ksmbd_vfs_kern_path_unlock(&path);
 	}
 	rc = ksmbd_vfs_link(work, target_name, link_name);
 	if (rc)

fs/smb/server/vfs.c

@@ -66,13 +66,12 @@ int ksmbd_vfs_lock_parent(struct dentry *parent, struct dentry *child)
 	return 0;
 }
 
-static int ksmbd_vfs_path_lookup_locked(struct ksmbd_share_config *share_conf,
-					char *pathname, unsigned int flags,
-					struct path *parent_path,
-					struct path *path)
+static int ksmbd_vfs_path_lookup(struct ksmbd_share_config *share_conf,
+				 char *pathname, unsigned int flags,
+				 struct path *path, bool do_lock)
 {
 	struct qstr last;
-	struct filename *filename;
+	struct filename *filename __free(putname) = NULL;
 	struct path *root_share_path = &share_conf->vfs_path;
 	int err, type;
 	struct dentry *d;
@@ -89,51 +88,57 @@ static int ksmbd_vfs_path_lookup_locked(struct ksmbd_share_config *share_conf,
 		return PTR_ERR(filename);
 
 	err = vfs_path_parent_lookup(filename, flags,
-				     parent_path, &last, &type,
+				     path, &last, &type,
 				     root_share_path);
-	if (err) {
-		putname(filename);
+	if (err)
 		return err;
-	}
 
 	if (unlikely(type != LAST_NORM)) {
-		path_put(parent_path);
-		putname(filename);
+		path_put(path);
 		return -ENOENT;
 	}
 
-	err = mnt_want_write(parent_path->mnt);
-	if (err) {
-		path_put(parent_path);
-		putname(filename);
+	if (do_lock) {
+		err = mnt_want_write(path->mnt);
+		if (err) {
+			path_put(path);
+			return -ENOENT;
+		}
+
+		inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
+		d = lookup_one_qstr_excl(&last, path->dentry, 0);
+
+		if (!IS_ERR(d)) {
+			dput(path->dentry);
+			path->dentry = d;
+			return 0;
+		}
+		inode_unlock(path->dentry->d_inode);
+		mnt_drop_write(path->mnt);
+		path_put(path);
 		return -ENOENT;
 	}
 
-	inode_lock_nested(parent_path->dentry->d_inode, I_MUTEX_PARENT);
-	d = lookup_one_qstr_excl(&last, parent_path->dentry, 0);
-	if (IS_ERR(d))
-		goto err_out;
-
+	d = lookup_noperm_unlocked(&last, path->dentry);
+	if (!IS_ERR(d) && d_is_negative(d)) {
+		dput(d);
+		d = ERR_PTR(-ENOENT);
+	}
+	if (IS_ERR(d)) {
+		path_put(path);
+		return -ENOENT;
+	}
+	dput(path->dentry);
 	path->dentry = d;
-	path->mnt = mntget(parent_path->mnt);
 
 	if (test_share_config_flag(share_conf, KSMBD_SHARE_FLAG_CROSSMNT)) {
 		err = follow_down(path, 0);
 		if (err < 0) {
 			path_put(path);
-			goto err_out;
+			return -ENOENT;
 		}
 	}
-
-	putname(filename);
 	return 0;
-
-err_out:
-	inode_unlock(d_inode(parent_path->dentry));
-	mnt_drop_write(parent_path->mnt);
-	path_put(parent_path);
-	putname(filename);
-	return -ENOENT;
 }
 
 void ksmbd_vfs_query_maximal_access(struct mnt_idmap *idmap,
@@ -1198,38 +1203,28 @@ static int ksmbd_vfs_lookup_in_dir(const struct path *dir, char *name,
 	return ret;
 }
 
-/**
- * ksmbd_vfs_kern_path_locked() - lookup a file and get path info
- * @work:		work
- * @filepath:		file path that is relative to share
- * @flags:		lookup flags
- * @parent_path:	if lookup succeed, return parent_path info
- * @path:		if lookup succeed, return path info
- * @caseless:	caseless filename lookup
- *
- * Return:	0 on success, otherwise error
- */
-int ksmbd_vfs_kern_path_locked(struct ksmbd_work *work, char *filepath,
-			       unsigned int flags, struct path *parent_path,
-			       struct path *path, bool caseless)
+static
+int __ksmbd_vfs_kern_path(struct ksmbd_work *work, char *filepath,
+			  unsigned int flags,
+			  struct path *path, bool caseless, bool do_lock)
 {
 	struct ksmbd_share_config *share_conf = work->tcon->share_conf;
+	struct path parent_path;
 	size_t path_len, remain_len;
 	int err;
 
 retry:
-	err = ksmbd_vfs_path_lookup_locked(share_conf, filepath, flags, parent_path,
-					   path);
+	err = ksmbd_vfs_path_lookup(share_conf, filepath, flags, path, do_lock);
 	if (!err || !caseless)
 		return err;
 
 	path_len = strlen(filepath);
 	remain_len = path_len;
 
-	*parent_path = share_conf->vfs_path;
-	path_get(parent_path);
+	parent_path = share_conf->vfs_path;
+	path_get(&parent_path);
 
-	while (d_can_lookup(parent_path->dentry)) {
+	while (d_can_lookup(parent_path.dentry)) {
 		char *filename = filepath + path_len - remain_len;
 		char *next = strchrnul(filename, '/');
 		size_t filename_len = next - filename;
@@ -1238,10 +1233,10 @@ int ksmbd_vfs_kern_path_locked(struct ksmbd_work *work, char *filepath,
 		if (filename_len == 0)
 			break;
 
-		err = ksmbd_vfs_lookup_in_dir(parent_path, filename,
+		err = ksmbd_vfs_lookup_in_dir(&parent_path, filename,
 					      filename_len,
 					      work->conn->um);
-		path_put(parent_path);
+		path_put(&parent_path);
 		if (err)
 			goto out;
 		if (is_last) {
@@ -1254,7 +1249,7 @@ int ksmbd_vfs_kern_path_locked(struct ksmbd_work *work, char *filepath,
 				      share_conf->vfs_path.mnt,
 				      filepath,
 				      flags,
-				      parent_path);
+				      &parent_path);
 		next[0] = '/';
 		if (err)
 			goto out;
@@ -1263,17 +1258,59 @@ int ksmbd_vfs_kern_path_locked(struct ksmbd_work *work, char *filepath,
 	}
 
 	err = -EINVAL;
-	path_put(parent_path);
+	path_put(&parent_path);
 out:
 	return err;
 }
 
-void ksmbd_vfs_kern_path_unlock(struct path *parent_path, struct path *path)
+/**
+ * ksmbd_vfs_kern_path() - lookup a file and get path info
+ * @work:		work
+ * @filepath:		file path that is relative to share
+ * @flags:		lookup flags
+ * @path:		if lookup succeed, return path info
+ * @caseless:	caseless filename lookup
+ *
+ * Perform the lookup, possibly crossing over any mount point.
+ * On return no locks will be held and write-access to filesystem
+ * won't have been checked.
+ * Return:	0 if file was found, otherwise error
+ */
+int ksmbd_vfs_kern_path(struct ksmbd_work *work, char *filepath,
+			unsigned int flags,
+			struct path *path, bool caseless)
 {
-	inode_unlock(d_inode(parent_path->dentry));
-	mnt_drop_write(parent_path->mnt);
+	return __ksmbd_vfs_kern_path(work, filepath, flags, path,
+				     caseless, false);
+}
+
+/**
+ * ksmbd_vfs_kern_path_locked() - lookup a file and get path info
+ * @work:		work
+ * @filepath:		file path that is relative to share
+ * @flags:		lookup flags
+ * @path:		if lookup succeed, return path info
+ * @caseless:	caseless filename lookup
+ *
+ * Perform the lookup, but don't cross over any mount point.
+ * On return the parent of path->dentry will be locked and write-access to
+ * filesystem will have been gained.
+ * Return:	0 on if file was found, otherwise error
+ */
+int ksmbd_vfs_kern_path_locked(struct ksmbd_work *work, char *filepath,
+			       unsigned int flags,
+			       struct path *path, bool caseless)
+{
+	return __ksmbd_vfs_kern_path(work, filepath, flags, path,
+				     caseless, true);
+}
+
+void ksmbd_vfs_kern_path_unlock(struct path *path)
+{
+	/* While lock is still held, ->d_parent is safe */
+	inode_unlock(d_inode(path->dentry->d_parent));
+	mnt_drop_write(path->mnt);
 	path_put(path);
-	path_put(parent_path);
 }
 
 struct dentry *ksmbd_vfs_kern_path_create(struct ksmbd_work *work,

fs/smb/server/vfs.h

@@ -117,10 +117,13 @@ int ksmbd_vfs_xattr_stream_name(char *stream_name, char **xattr_stream_name,
 int ksmbd_vfs_remove_xattr(struct mnt_idmap *idmap,
 			   const struct path *path, char *attr_name,
 			   bool get_write);
+int ksmbd_vfs_kern_path(struct ksmbd_work *work, char *name,
+			unsigned int flags,
+			struct path *path, bool caseless);
 int ksmbd_vfs_kern_path_locked(struct ksmbd_work *work, char *name,
-			       unsigned int flags, struct path *parent_path,
+			       unsigned int flags,
 			       struct path *path, bool caseless);
-void ksmbd_vfs_kern_path_unlock(struct path *parent_path, struct path *path);
+void ksmbd_vfs_kern_path_unlock(struct path *path);
 struct dentry *ksmbd_vfs_kern_path_create(struct ksmbd_work *work,
 					  const char *name,
 					  unsigned int flags,