linux-kernel - Re: [PATCH 1/2] rcu: Do not release a wait-head from a GP kthread

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZekEiXZes38y_Rmq@localhost.localdomain>
Date: Thu, 7 Mar 2024 01:04:25 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: "Paul E . McKenney" <paulmck@...nel.org>, RCU <rcu@...r.kernel.org>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Boqun Feng <boqun.feng@...il.com>, Hillf Danton <hdanton@...a.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH 1/2] rcu: Do not release a wait-head from a GP kthread

Le Tue, Mar 05, 2024 at 08:57:19PM +0100, Uladzislau Rezki (Sony) a écrit :
> Fix a below race by not releasing a wait-head from the
> GP-kthread as it can lead for reusing it whereas a worker
> can still access it thus execute newly added callbacks too
> early.
> 
> CPU 0                              CPU 1
> -----                              -----
> 
> // wait_tail == HEAD1
> rcu_sr_normal_gp_cleanup() {
>     // has passed SR_MAX_USERS_WAKE_FROM_GP
>     wait_tail->next = next;
>     // done_tail = HEAD1
>     smp_store_release(&rcu_state.srs_done_tail, wait_tail);
>     queue_work() {
>         test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)
>         __queue_work()
>     }
> }
> 
>                                set_work_pool_and_clear_pending()
>                                rcu_sr_normal_gp_cleanup_work() {
> // new GP, wait_tail == HEAD2
> rcu_sr_normal_gp_cleanup() {
>     // executes all completion, but stop at HEAD1
>     wait_tail->next = HEAD1;
>     // done_tail = HEAD2
>     smp_store_release(&rcu_state.srs_done_tail, wait_tail);
>     queue_work() {
>         test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)
>         __queue_work()
>     }
> }
>                                  // done = HEAD2
>                                  done = smp_load_acquire(&rcu_state.srs_done_tail);
>                                  // head = HEAD1
>                                  head = done->next;
>                                  done->next = NULL;
>                                  llist_for_each_safe() {
>                                  // completes all callbacks, release HEAD1
>                                  }
>                                }
>                                // Process second queue
>                                set_work_pool_and_clear_pending()
>                                rcu_sr_normal_gp_cleanup_work() {
>                                // done = HEAD2
>                                done = smp_load_acquire(&rcu_state.srs_done_tail);
> 
> // new GP, wait_tail == HEAD3
> rcu_sr_normal_gp_cleanup() {
>     // Finds HEAD2 with ->next == NULL at the end
>     rcu_sr_put_wait_head(HEAD2)
>     ...
> 
> // A few more GPs later
> rcu_sr_normal_gp_init() {
>      HEAD2 = rcu_sr_get_wait_head();
>      llist_add(HEAD2, &rcu_state.srs_next);
>                                // head == rcu_state.srs_next
>                                head = done->next;
>                                done->next = NULL;
>                                llist_for_each_safe() {
>                                 // EXECUTE CALLBACKS TOO EARLY!!!
>                                 }
>                                }
> 
> Reported-by: Frederic Weisbecker <frederic@...nel.org>
> Fixes: 05a10b921000 ("rcu: Support direct wake-up of synchronize_rcu() users")
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>