From patchwork Mon Apr 6 18:58:27 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 11476345 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 91F6D92C for ; Mon, 6 Apr 2020 18:58:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5E8B7206B8 for ; Mon, 6 Apr 2020 18:58:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RFeSGK4T" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725933AbgDFS6s (ORCPT ); Mon, 6 Apr 2020 14:58:48 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:27225 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725895AbgDFS6r (ORCPT ); Mon, 6 Apr 2020 14:58:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586199525; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=QLx4/sdG9v1nmxm7Nxx7v62MFnknzk0r6dRJ8swzlNk=; b=RFeSGK4TfryShPgDBp05K974pmmp+h3O701SH5FOb2W3K/VGCL+x4hBWCINf+4AnF3/40J WQ+G9FPS6FgWo6WI3MisW2HxAGZAcmFVjmyKPlkDaCy4Qu50jRS0a+Xpo+Rcu7geJbchgC y6qSLqq3xOZ7l+wrxs6JP9bZ/fJ8nHA= 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-442-T2oxZoLWMue6HCaiqW986Q-1; Mon, 06 Apr 2020 14:58:42 -0400 X-MC-Unique: T2oxZoLWMue6HCaiqW986Q-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 095A4DBA5; Mon, 6 Apr 2020 18:58:41 +0000 (UTC) Received: from llong.com (ovpn-115-20.rdu2.redhat.com [10.10.115.20]) by smtp.corp.redhat.com (Postfix) with ESMTP id 58A9F19C4F; Mon, 6 Apr 2020 18:58:36 +0000 (UTC) From: Waiman Long To: Andrew Morton , David Howells , Jarkko Sakkinen , James Morris , "Serge E. Hallyn" Cc: linux-mm@kvack.org, keyrings@vger.kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Joe Perches , Matthew Wilcox , David Rientjes , Waiman Long Subject: [PATCH v2] mm: Add kvfree_sensitive() for freeing sensitive data objects Date: Mon, 6 Apr 2020 14:58:27 -0400 Message-Id: <20200406185827.22249-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: keyrings-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: keyrings@vger.kernel.org For kvmalloc'ed data object that contains sensitive information like cryptographic key, we need to make sure that the buffer is always cleared before freeing it. Using memset() alone for buffer clearing may not provide certainty as the compiler may compile it away. To be sure, the special memzero_explicit() has to be used. This patch introduces a new kvfree_sensitive() for freeing those sensitive data objects allocated by kvmalloc(). The relevnat places where kvfree_sensitive() can be used are modified to use it. Fixes: 4f0882491a14 ("KEYS: Avoid false positive ENOMEM error on key read") Suggested-by: Linus Torvalds Signed-off-by: Waiman Long --- include/linux/mm.h | 1 + mm/util.c | 18 ++++++++++++++++++ security/keys/internal.h | 11 ----------- security/keys/keyctl.c | 16 +++++----------- 4 files changed, 24 insertions(+), 22 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 7dd5c4ccbf85..9b3130b20f42 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -757,6 +757,7 @@ static inline void *kvcalloc(size_t n, size_t size, gfp_t flags) } extern void kvfree(const void *addr); +extern void kvfree_sensitive(const void *addr, size_t len); static inline int compound_mapcount(struct page *page) { diff --git a/mm/util.c b/mm/util.c index 988d11e6c17c..01e210766f3d 100644 --- a/mm/util.c +++ b/mm/util.c @@ -604,6 +604,24 @@ void kvfree(const void *addr) } EXPORT_SYMBOL(kvfree); +/** + * kvfree_sensitive - free a data object containing sensitive information + * @addr - address of the data object to be freed + * @len - length of the data object + * + * Use the special memzero_explicit() function to clear the content of a + * kvmalloc'ed object containing sensitive data to make sure that the + * compiler won't optimize out the data clearing. + */ +void kvfree_sensitive(const void *addr, size_t len) +{ + if (likely(!ZERO_OR_NULL_PTR(addr))) { + memzero_explicit((void *)addr, len); + kvfree(addr); + } +} +EXPORT_SYMBOL(kvfree_sensitive); + static inline void *__page_rmapping(struct page *page) { unsigned long mapping; diff --git a/security/keys/internal.h b/security/keys/internal.h index 6d0ca48ae9a5..153d35c20d3d 100644 --- a/security/keys/internal.h +++ b/security/keys/internal.h @@ -350,15 +350,4 @@ static inline void key_check(const struct key *key) #define key_check(key) do {} while(0) #endif - -/* - * Helper function to clear and free a kvmalloc'ed memory object. - */ -static inline void __kvzfree(const void *addr, size_t len) -{ - if (addr) { - memset((void *)addr, 0, len); - kvfree(addr); - } -} #endif /* _INTERNAL_H */ diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c index 5e01192e222a..edde63a63007 100644 --- a/security/keys/keyctl.c +++ b/security/keys/keyctl.c @@ -142,10 +142,7 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type, key_ref_put(keyring_ref); error3: - if (payload) { - memzero_explicit(payload, plen); - kvfree(payload); - } + kvfree_sensitive(payload, plen); error2: kfree(description); error: @@ -360,7 +357,7 @@ long keyctl_update_key(key_serial_t id, key_ref_put(key_ref); error2: - __kvzfree(payload, plen); + kvfree_sensitive(payload, plen); error: return ret; } @@ -914,7 +911,7 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen) */ if (ret > key_data_len) { if (unlikely(key_data)) - __kvzfree(key_data, key_data_len); + kvfree_sensitive(key_data, key_data_len); key_data_len = ret; continue; /* Allocate buffer */ } @@ -923,7 +920,7 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen) ret = -EFAULT; break; } - __kvzfree(key_data, key_data_len); + kvfree_sensitive(key_data, key_data_len); key_put_out: key_put(key); @@ -1225,10 +1222,7 @@ long keyctl_instantiate_key_common(key_serial_t id, keyctl_change_reqkey_auth(NULL); error2: - if (payload) { - memzero_explicit(payload, plen); - kvfree(payload); - } + kvfree_sensitive(payload, plen); error: return ret; }