ksmbd: fix NULL pointer dereference in smb2_get_info_filesystem()

If share is , share->path is NULL and it cause NULL pointer
dereference issue.

Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-20479
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/smb2pdu.c

@@ -4885,6 +4885,9 @@ static int smb2_get_info_filesystem(struct ksmbd_work *work,
 	int rc = 0, len;
 	int fs_infoclass_size = 0;
 
+	if (!share->path)
+		return -EIO;
+
 	rc = kern_path(share->path, LOOKUP_NO_SYMLINKS, &path);
 	if (rc) {
 		pr_err("cannot create vfs path\n");