From mboxrd@z Thu Jan 1 00:00:00 1970 From: Amol Grover Subject: [PATCH 2/3] cred: Do not use RCU primitives to access cred pointer Date: Fri, 7 Feb 2020 23:35:04 +0530 Message-ID: <20200207180504.4200-2-frextrite@gmail.com> References: <20200207180504.4200-1-frextrite@gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20200207180504.4200-1-frextrite@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , James Morris , Thomas Gleixner Peter Zijlstra , Jann Horn , David Howells , Shakeel Butt , "Eric W . Biederman" , Andrew Morton , Paul Moore , Eric Paris Cc: linux-kernel-mentees@lists.linuxfoundation.org, linux-kernel@vger.kernel.org, linux-audit@redhat.com, Joel Fernandes , Madhuparna Bhowmik , "Paul E . McKenney" , Amol Grover List-Id: linux-audit@redhat.com Since task_struct::cred can only be used task-synchronously, and is not visible to other threads under RCU context, we do not require RCU primitives to read/write to it and incur heavy barriers. Suggested-by: Jann Horn Co-developed-by: Joel Fernandes (Google) Signed-off-by: Joel Fernandes (Google) Signed-off-by: Amol Grover --- include/linux/cred.h | 5 ++--- kernel/cred.c | 6 +++--- 2 files changed, 5 insertions(+), 6 deletions(-) diff --git a/include/linux/cred.h b/include/linux/cred.h index 18639c069263..5973791e5fe4 100644 --- a/include/linux/cred.h +++ b/include/linux/cred.h @@ -291,11 +291,10 @@ static inline void put_cred(const struct cred *_cred) /** * current_cred - Access the current task's subjective credentials * - * Access the subjective credentials of the current task. RCU-safe, - * since nobody else can modify it. + * Access the subjective credentials of the current task. */ #define current_cred() \ - rcu_dereference_protected(current->cred, 1) + (current->cred) /** * current_real_cred - Access the current task's objective credentials diff --git a/kernel/cred.c b/kernel/cred.c index 809a985b1793..3956c31d068d 100644 --- a/kernel/cred.c +++ b/kernel/cred.c @@ -485,7 +485,7 @@ int commit_creds(struct cred *new) if (new->user != old->user) atomic_inc(&new->user->processes); rcu_assign_pointer(task->real_cred, new); - rcu_assign_pointer(task->cred, new); + task->cred = new; if (new->user != old->user) atomic_dec(&old->user->processes); alter_cred_subscribers(old, -2); @@ -562,7 +562,7 @@ const struct cred *override_creds(const struct cred *new) */ get_new_cred((struct cred *)new); alter_cred_subscribers(new, 1); - rcu_assign_pointer(current->cred, new); + current->cred = new; alter_cred_subscribers(old, -1); kdebug("override_creds() = %p{%d,%d}", old, @@ -590,7 +590,7 @@ void revert_creds(const struct cred *old) validate_creds(old); validate_creds(override); alter_cred_subscribers(old, 1); - rcu_assign_pointer(current->cred, old); + current->cred = old; alter_cred_subscribers(override, -1); put_cred(override); } -- 2.24.1