Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755809AbdHYJm5 (ORCPT ); Fri, 25 Aug 2017 05:42:57 -0400 Received: from mga07.intel.com ([134.134.136.100]:18356 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755510AbdHYJm4 (ORCPT ); Fri, 25 Aug 2017 05:42:56 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.41,424,1498546800"; d="scan'208";a="893999843" From: Elena Reshetova To: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, peterz@infradead.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk, tj@kernel.org, mingo@redhat.com, hannes@cmpxchg.org, lizefan@huawei.com, acme@kernel.org, alexander.shishkin@linux.intel.com, eparis@redhat.com, akpm@linux-foundation.org, arnd@arndb.de, luto@kernel.org, keescook@chromium.org, tglx@linutronix.de, dvhart@infradead.org, ebiederm@xmission.com, Elena Reshetova Subject: [PATCH 12/15] groups: convert group_info.usage to refcount_t Date: Fri, 25 Aug 2017 12:41:29 +0300 Message-Id: <1503654092-15471-13-git-send-email-elena.reshetova@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1503654092-15471-1-git-send-email-elena.reshetova@intel.com> References: <1503654092-15471-1-git-send-email-elena.reshetova@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2884 Lines: 94 atomic_t variables are currently used to implement reference counters with the following properties: - counter is initialized to 1 using atomic_set() - a resource is freed upon counter reaching zero - once counter reaches zero, its further increments aren't allowed - counter schema uses basic atomic operations (set, inc, inc_not_zero, dec_and_test, etc.) Such atomic variables should be converted to a newly provided refcount_t type and API that prevents accidental counter overflows and underflows. This is important since overflows and underflows can lead to use-after-free situation and be exploitable. The variable group_info.usage is used as pure reference counter. Convert it to refcount_t and fix up the operations. Suggested-by: Kees Cook Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Signed-off-by: Elena Reshetova --- include/linux/cred.h | 7 ++++--- kernel/cred.c | 2 +- kernel/groups.c | 2 +- 3 files changed, 6 insertions(+), 5 deletions(-) diff --git a/include/linux/cred.h b/include/linux/cred.h index 099058e..00948dd 100644 --- a/include/linux/cred.h +++ b/include/linux/cred.h @@ -17,6 +17,7 @@ #include #include #include +#include #include #include #include @@ -28,7 +29,7 @@ struct inode; * COW Supplementary groups list */ struct group_info { - atomic_t usage; + refcount_t usage; int ngroups; kgid_t gid[0]; } __randomize_layout; @@ -44,7 +45,7 @@ struct group_info { */ static inline struct group_info *get_group_info(struct group_info *gi) { - atomic_inc(&gi->usage); + refcount_inc(&gi->usage); return gi; } @@ -54,7 +55,7 @@ static inline struct group_info *get_group_info(struct group_info *gi) */ #define put_group_info(group_info) \ do { \ - if (atomic_dec_and_test(&(group_info)->usage)) \ + if (refcount_dec_and_test(&(group_info)->usage)) \ groups_free(group_info); \ } while (0) diff --git a/kernel/cred.c b/kernel/cred.c index ecf0365..8122d7c 100644 --- a/kernel/cred.c +++ b/kernel/cred.c @@ -36,7 +36,7 @@ do { \ static struct kmem_cache *cred_jar; /* init to 2 - one for init_task, one to ensure it is never freed */ -struct group_info init_groups = { .usage = ATOMIC_INIT(2) }; +struct group_info init_groups = { .usage = REFCOUNT_INIT(2) }; /* * The initial credentials for the initial task diff --git a/kernel/groups.c b/kernel/groups.c index 434f666..5fc6e21 100644 --- a/kernel/groups.c +++ b/kernel/groups.c @@ -23,7 +23,7 @@ struct group_info *groups_alloc(int gidsetsize) if (!gi) return NULL; - atomic_set(&gi->usage, 1); + refcount_set(&gi->usage, 1); gi->ngroups = gidsetsize; return gi; } -- 2.7.4