| 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
| ||
|
Message-ID: <4d331659-badd-749d-fba1-271543631a8a@huawei.com>
Date: Tue, 9 Apr 2024 22:15:39 +0800
From: Li Lingfeng <lilingfeng3@...wei.com>
To: Mikulas Patocka <mpatocka@...hat.com>, Linus Torvalds
<torvalds@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>
CC: <linux-kernel@...r.kernel.org>, <dm-devel@...ts.linux.dev>, Mike Snitzer
<msnitzer@...hat.com>, Ignat Korchagin <ignat@...udflare.com>, Damien Le Moal
<damien.lemoal@....com>, Bob Liu <bob.liu@...cle.com>, Hou Tao
<houtao1@...wei.com>, Nathan Huckleberry <nhuck@...gle.com>, Peter Zijlstra
<peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>, "yukuai (C)"
<yukuai3@...wei.com>, yangerkun <yangerkun@...wei.com>, "zhangyi (F)"
<yi.zhang@...wei.com>, <lilingfeng3@...wei.com>, Li Lingfeng
<lilingfeng@...weicloud.com>
Subject: Re: [PATCH] softirq: fix memory corruption when freeing
tasklet_struct
Hi
I tried to reproduce the problem by adding mdelay() in
tasklet_action_common() after t->func() but failed.
Since cc->io_queue is created without WQ_UNBOUND, the work queued to it
will be executed by the CPU which queued the work, which means
bio_endio() will not be called until tasklet_action_common has finished.
Could you please clarify how to reproduce the problem mentioned here?
Thanks
在 2024/1/26 2:29, Mikulas Patocka 写道:
> Hi
>
> There's a problem with the tasklet API - there is no reliable way how to
> free a structure that contains tasklet_struct. The problem is that the
> function tasklet_action_common calls task_unlock(t) after it called the
> callback. If the callback does something that frees tasklet_struct,
> task_unlock(t) would write into free memory.
>
> dm-crypt does this - it schedules a tasklet with tasklet_schedule, it does
> encryption inside the tasklet handler (because it performs better than
> doing the encryption in a workqueue), then it submits a workqueue entry
> and calls bio_endio from the workqueue entry.
>
> However, if the workqueue preempts ksoftirqd, this race condition happens:
>
> ksoftirqd:
> * tasklet_action_common
> * t->func(t->data) (that points to kcryptd_crypt_tasklet)
> * kcryptd_crypt_tasklet
> * kcryptd_crypt
> * kcryptd_crypt_read_convert
> * crypt_dec_pending
> * queue_work(cc->io_queue, &io->work);
> now we switch to the workqueue process:
> * kcryptd_io_bio_endio
> * bio_endio(io->base_bio) (this calls clone_endio)
> * clone_endio
> * free_tio
> * bio_put(clone) - the bio is freed
> now we switch back to ksoftirqd:
> * tasklet_action_common calls task_unlock(t)
> * task_unlock(t) touches memory that was already freed when the bio was freed
>
> dm-verity has a similar problem.
>
> In order to fix this bug, I am proposing to add a new flag
> TASKLET_STATE_ONESHOT. The flag indicates that the tasklet will be
> submitted only once and it prevents tasklet_action_common from touching
> the tasklet after the callback completed.
>
> If you have another idea how to solve this bug, let me know.
>
> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
> Fixes: 39d42fa96ba1 ("dm crypt: add flags to optionally bypass kcryptd workqueues")
> Fixes: 5721d4e5a9cd ("dm verity: Add optional "try_verify_in_tasklet" feature")
> Cc: stable@...r.kernel.org # v5.9+
>
> ---
> drivers/md/dm-crypt.c | 1 +
> drivers/md/dm-verity-target.c | 1 +
> include/linux/interrupt.h | 9 ++++++++-
> kernel/softirq.c | 22 +++++++++++++++-------
> 4 files changed, 25 insertions(+), 8 deletions(-)
>
> Index: linux-2.6/drivers/md/dm-crypt.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-crypt.c 2024-01-18 19:18:30.000000000 +0100
> +++ linux-2.6/drivers/md/dm-crypt.c 2024-01-25 16:42:17.000000000 +0100
> @@ -2265,6 +2265,7 @@ static void kcryptd_queue_crypt(struct d
> if (in_hardirq() || irqs_disabled()) {
> io->in_tasklet = true;
> tasklet_init(&io->tasklet, kcryptd_crypt_tasklet, (unsigned long)&io->work);
> + tasklet_set_oneshot(&io->tasklet);
> tasklet_schedule(&io->tasklet);
> return;
> }
> Index: linux-2.6/include/linux/interrupt.h
> ===================================================================
> --- linux-2.6.orig/include/linux/interrupt.h 2023-11-13 17:39:50.000000000 +0100
> +++ linux-2.6/include/linux/interrupt.h 2024-01-25 16:41:52.000000000 +0100
> @@ -684,7 +684,9 @@ struct tasklet_struct name = { \
> enum
> {
> TASKLET_STATE_SCHED, /* Tasklet is scheduled for execution */
> - TASKLET_STATE_RUN /* Tasklet is running (SMP only) */
> + TASKLET_STATE_RUN, /* Tasklet is running (SMP only) */
> + TASKLET_STATE_ONESHOT /* Don't unlock the tasklet after the callback
> + to avoid writing to free memory */
> };
>
> #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
> @@ -756,6 +758,11 @@ extern void tasklet_init(struct tasklet_
> extern void tasklet_setup(struct tasklet_struct *t,
> void (*callback)(struct tasklet_struct *));
>
> +static inline void tasklet_set_oneshot(struct tasklet_struct *t)
> +{
> + __set_bit(TASKLET_STATE_ONESHOT, &t->state);
> +}
> +
> /*
> * Autoprobing for irqs:
> *
> Index: linux-2.6/kernel/softirq.c
> ===================================================================
> --- linux-2.6.orig/kernel/softirq.c 2023-10-31 15:31:42.000000000 +0100
> +++ linux-2.6/kernel/softirq.c 2024-01-25 17:10:03.000000000 +0100
> @@ -774,18 +774,26 @@ static void tasklet_action_common(struct
>
> if (tasklet_trylock(t)) {
> if (!atomic_read(&t->count)) {
> + /*
> + * If oneshot is set, we must not touch the
> + * tasklet after the callback.
> + */
> + bool oneshot = test_bit(TASKLET_STATE_ONESHOT, &t->state);
> if (tasklet_clear_sched(t)) {
> if (t->use_callback) {
> - trace_tasklet_entry(t, t->callback);
> - t->callback(t);
> - trace_tasklet_exit(t, t->callback);
> + void (*callback)(struct tasklet_struct *) = t->callback;
> + trace_tasklet_entry(t, callback);
> + callback(t);
> + trace_tasklet_exit(t, callback);
> } else {
> - trace_tasklet_entry(t, t->func);
> - t->func(t->data);
> - trace_tasklet_exit(t, t->func);
> + void (*func)(unsigned long) = t->func;
> + trace_tasklet_entry(t, func);
> + func(t->data);
> + trace_tasklet_exit(t, func);
> }
> }
> - tasklet_unlock(t);
> + if (!oneshot)
> + tasklet_unlock(t);
> continue;
> }
> tasklet_unlock(t);
> Index: linux-2.6/drivers/md/dm-verity-target.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-verity-target.c 2024-01-18 19:18:30.000000000 +0100
> +++ linux-2.6/drivers/md/dm-verity-target.c 2024-01-25 18:12:09.000000000 +0100
> @@ -676,6 +676,7 @@ static void verity_end_io(struct bio *bi
>
> if (static_branch_unlikely(&use_tasklet_enabled) && io->v->use_tasklet) {
> tasklet_init(&io->tasklet, verity_tasklet, (unsigned long)io);
> + tasklet_set_oneshot(&io->tasklet);
> tasklet_schedule(&io->tasklet);
> } else {
> INIT_WORK(&io->work, verity_work);
>
Powered by blists - more mailing lists