On 2023-04-13 05:32, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> Our test reports a uaf for 'mddev->sync_thread':
>
> T1 T2
> md_start_sync
> md_register_thread
> // mddev->sync_thread is set
> raid1d
> md_check_recovery
> md_reap_sync_thread
> md_unregister_thread
> kfree
>
> md_wakeup_thread
> wake_up
> ->sync_thread was freed
>
> Root cause is that there is a small windown between register thread and
> wake up thread, where the thread can be freed concurrently.
>
> Currently, a global spinlock 'pers_lock' is borrowed to protect
> 'mddev->thread', this problem can be fixed likewise, however, there are
> similar problems elsewhere, and use a global lock for all the cases is
> not good.
>
> This patch protect all md_thread with rcu.
>
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
> drivers/md/md-bitmap.c | 10 ++++--
> drivers/md/md-cluster.c | 7 ++--
> drivers/md/md-multipath.c | 4 +--
> drivers/md/md.c | 69 ++++++++++++++++++---------------------
> drivers/md/md.h | 8 ++---
> drivers/md/raid1.c | 7 ++--
> drivers/md/raid1.h | 2 +-
> drivers/md/raid10.c | 21 +++++++-----
> drivers/md/raid10.h | 2 +-
> drivers/md/raid5-cache.c | 22 ++++++++-----
> drivers/md/raid5.c | 15 +++++----
> drivers/md/raid5.h | 2 +-
> 12 files changed, 91 insertions(+), 78 deletions(-)
>
> diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
> index 29fd41ef55a6..ab27f66dbb1f 100644
> --- a/drivers/md/md-bitmap.c
> +++ b/drivers/md/md-bitmap.c
> @@ -1221,13 +1221,19 @@ static bitmap_counter_t *md_bitmap_get_counter(struct bitmap_counts *bitmap,
> static void mddev_set_timeout(struct mddev *mddev, unsigned long timeout,
> bool force)
> {
> - struct md_thread *thread = mddev->thread;
> + struct md_thread *thread;
> +
> + rcu_read_lock();
> + thread = rcu_dereference(mddev->thread);
>
> if (!thread)
> - return;
> + goto out;
>
> if (force || thread->timeout < MAX_SCHEDULE_TIMEOUT)
> thread->timeout = timeout;
> +
> +out:
> + rcu_read_unlock();
> }
>
> /*
> diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
> index 10e0c5381d01..672dfa6a40ec 100644
> --- a/drivers/md/md-cluster.c
> +++ b/drivers/md/md-cluster.c
> @@ -362,8 +362,8 @@ static void __recover_slot(struct mddev *mddev, int slot)
>
> set_bit(slot, &cinfo->recovery_map);
> if (!cinfo->recovery_thread) {
> - cinfo->recovery_thread = md_register_thread(recover_bitmaps,
> - mddev, "recover");
> + rcu_assign_pointer(cinfo->recovery_thread,
> + md_register_thread(recover_bitmaps, mddev, "recover"));
> if (!cinfo->recovery_thread) {
> pr_warn("md-cluster: Could not create recovery thread\n");
> return;
> @@ -889,7 +889,8 @@ static int join(struct mddev *mddev, int nodes)
> }
> /* Initiate the communication resources */
> ret = -ENOMEM;
> - cinfo->recv_thread = md_register_thread(recv_daemon, mddev, "cluster_recv");
> + rcu_assign_pointer(cinfo->recv_thread,
> + md_register_thread(recv_daemon, mddev, "cluster_recv"));
> if (!cinfo->recv_thread) {
This looks like it'll hit sparse warnings. without an
rcu_access_pointer(). Might be nicer to use a temporary variable, check
that it's not null, then call rcu_assign_pointer().
--
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