From patchwork Sun Mar 8 17:04:10 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 11425777 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id EE9C3138D for ; Sun, 8 Mar 2020 17:04:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CEE24208C3 for ; Sun, 8 Mar 2020 17:04:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hxM9Rbgp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726453AbgCHREg (ORCPT ); Sun, 8 Mar 2020 13:04:36 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:56373 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726414AbgCHREe (ORCPT ); Sun, 8 Mar 2020 13:04:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1583687073; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:in-reply-to:in-reply-to:references:references; bh=/kCt/AmtzbGfbmI9H2k3aFKT17BIacOKpSUSO5iFTyU=; b=hxM9RbgpPBZFRJGjqW1RswjJ8DH8FNoIegj5knWGuF4CSnSzNZ7k6U1DG37gvS8upGCJHP AqshmHD2uWlPk4GtgR83V+ptKCP+GVjes4F5ytkGv1M2Jzp/STRQB/umhKmEZcjxRtxmqS 1cpYLCv3c5PVaCRdBFPq53jMpO4sjbs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-460-mU65sZXEOp2RH0nVCNxe6Q-1; Sun, 08 Mar 2020 13:04:31 -0400 X-MC-Unique: mU65sZXEOp2RH0nVCNxe6Q-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9D17B800D50; Sun, 8 Mar 2020 17:04:29 +0000 (UTC) Received: from llong.com (ovpn-120-251.rdu2.redhat.com [10.10.120.251]) by smtp.corp.redhat.com (Postfix) with ESMTP id E94F85D9C5; Sun, 8 Mar 2020 17:04:27 +0000 (UTC) From: Waiman Long To: David Howells , Jarkko Sakkinen , James Morris , "Serge E. Hallyn" , Mimi Zohar Cc: keyrings@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-integrity@vger.kernel.org, Sumit Garg , Jerry Snitselaar , Roberto Sassu , Eric Biggers , Chris von Recklinghausen , Waiman Long Subject: [PATCH v2 2/2] KEYS: Avoid false positive ENOMEM error on key read Date: Sun, 8 Mar 2020 13:04:10 -0400 Message-Id: <20200308170410.14166-3-longman@redhat.com> In-Reply-To: <20200308170410.14166-1-longman@redhat.com> References: <20200308170410.14166-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: keyrings-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: keyrings@vger.kernel.org By allocating a kernel buffer with an user-supplied buffer length, it is possible that a false positive ENOMEM error may be returned because the user-supplied length is just too large even if the system do have enough memory to hold the actual key data. To reduce this possibility, we set a threshold (1024) over which we do check the actual key length first before allocating a buffer of the right size to hold it. Signed-off-by: Waiman Long --- security/keys/keyctl.c | 46 ++++++++++++++++++++++++++++++++---------- 1 file changed, 35 insertions(+), 11 deletions(-) diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c index 89a14e71eb0a..662a638a680d 100644 --- a/security/keys/keyctl.c +++ b/security/keys/keyctl.c @@ -855,28 +855,52 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen) * deadlock involving page fault and mmap_sem. */ char *tmpbuf = NULL; + size_t tbuflen = buflen; - if (buffer && buflen) { - tmpbuf = kmalloc(buflen, GFP_KERNEL); + /* + * We don't want an erronous -ENOMEM error due to an + * arbitrary large user-supplied buflen. So if buflen + * exceeds a threshold (1024 bytes in this case), we call + * the read method twice. The first time to get the buffer + * length and the second time to read out the key data. + * + * N.B. All the read methods will return the required + * buffer length with a NULL input buffer or when + * the input buffer length isn't large enough. + */ + if (buflen && buffer && (buflen <= 0x400)) { +allocbuf: + tmpbuf = kmalloc(tbuflen, GFP_KERNEL); if (!tmpbuf) { ret = -ENOMEM; goto error2; } } + down_read(&key->sem); ret = key_validate(key); if (ret == 0) - ret = key->type->read(key, tmpbuf, buflen); + ret = key->type->read(key, tmpbuf, tbuflen); up_read(&key->sem); - /* - * Read methods will just return the required length - * without any copying if the provided length isn't big - * enough. - */ - if ((ret > 0) && (ret <= buflen) && buffer && - copy_to_user(buffer, tmpbuf, ret)) - ret = -EFAULT; + if ((ret > 0) && (ret <= buflen) && buffer) { + /* + * It is possible, though unlikely, that the key + * changes in between the up_read->down_read period. + * If the key becomes longer, we will have to + * allocate a larger buffer and redo the key read + * again. + */ + if (!tmpbuf || unlikely(ret > tbuflen)) { + tbuflen = ret; + if (unlikely(tmpbuf)) + kzfree(tmpbuf); + goto allocbuf; + } + + if (copy_to_user(buffer, tmpbuf, ret)) + ret = -EFAULT; + } if (tmpbuf) kzfree(tmpbuf);