[PATCH -next v6 5/5] md: protect md_thread with rcu

From: Yu Kuai
Date: Thu Apr 13 2023 - 07:33:46 EST

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) {
pr_err("md-cluster: cannot allocate memory for recv_thread!\n");
goto err;
diff --git a/drivers/md/md-multipath.c b/drivers/md/md-multipath.c
index 66edf5e72bd6..92c45be203d7 100644
--- a/drivers/md/md-multipath.c
+++ b/drivers/md/md-multipath.c
@@ -400,8 +400,8 @@ static int multipath_run (struct mddev *mddev)
if (ret)
goto out_free_conf;

- mddev->thread = md_register_thread(multipathd, mddev,
- "multipath");
+ rcu_assign_pointer(mddev->thread,
+ md_register_thread(multipathd, mddev, "multipath"));
if (!mddev->thread)
goto out_free_conf;

diff --git a/drivers/md/md.c b/drivers/md/md.c
index e3c30500bd15..f680eccf4197 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -70,11 +70,7 @@
#include "md-bitmap.h"
#include "md-cluster.h"

-/* pers_list is a list of registered personalities protected
- * by pers_lock.
- * pers_lock does extra service to protect accesses to
- * mddev->thread when the mutex cannot be held.
- */
+/* pers_list is a list of registered personalities protected by pers_lock. */
static LIST_HEAD(pers_list);
static DEFINE_SPINLOCK(pers_lock);

@@ -92,7 +88,7 @@ static struct workqueue_struct *md_rdev_misc_wq;
static int remove_and_add_spares(struct mddev *mddev,
struct md_rdev *this);
static void mddev_detach(struct mddev *mddev);
-static void md_wakeup_thread_directly(struct md_thread *thread);
+static void md_wakeup_thread_directly(struct md_thread __rcu *thread);

enum md_ro_state {
MD_RDWR,
@@ -458,8 +454,10 @@ static void md_submit_bio(struct bio *bio)
*/
void mddev_suspend(struct mddev *mddev)
{
- WARN_ON_ONCE(mddev->thread && current == mddev->thread->tsk);
- lockdep_assert_held(&mddev->reconfig_mutex);
+ struct md_thread *thread = rcu_dereference_protected(mddev->thread,
+ lockdep_is_held(&mddev->reconfig_mutex));
+
+ WARN_ON_ONCE(thread && current == thread->tsk);
if (mddev->suspended++)
return;
wake_up(&mddev->sb_wait);
@@ -801,13 +799,8 @@ void mddev_unlock(struct mddev *mddev)
} else
mutex_unlock(&mddev->reconfig_mutex);

- /* As we've dropped the mutex we need a spinlock to
- * make sure the thread doesn't disappear
- */
- spin_lock(&pers_lock);
md_wakeup_thread(mddev->thread);
wake_up(&mddev->sb_wait);
- spin_unlock(&pers_lock);
}
EXPORT_SYMBOL_GPL(mddev_unlock);

@@ -7891,19 +7884,29 @@ static int md_thread(void *arg)
return 0;
}

-static void md_wakeup_thread_directly(struct md_thread *thread)
+static void md_wakeup_thread_directly(struct md_thread __rcu *thread)
{
- if (thread)
- wake_up_process(thread->tsk);
+ struct md_thread *t;
+
+ rcu_read_lock();
+ t = rcu_dereference(thread);
+ if (t)
+ wake_up_process(t->tsk);
+ rcu_read_unlock();
}

-void md_wakeup_thread(struct md_thread *thread)
+void md_wakeup_thread(struct md_thread __rcu *thread)
{
- if (thread) {
- pr_debug("md: waking up MD thread %s.\n", thread->tsk->comm);
- set_bit(THREAD_WAKEUP, &thread->flags);
- wake_up(&thread->wqueue);
+ struct md_thread *t;
+
+ rcu_read_lock();
+ t = rcu_dereference(thread);
+ if (t) {
+ pr_debug("md: waking up MD thread %s.\n", t->tsk->comm);
+ set_bit(THREAD_WAKEUP, &t->flags);
+ wake_up(&t->wqueue);
}
+ rcu_read_unlock();
}
EXPORT_SYMBOL(md_wakeup_thread);

@@ -7933,22 +7936,15 @@ struct md_thread *md_register_thread(void (*run) (struct md_thread *),
}
EXPORT_SYMBOL(md_register_thread);

-void md_unregister_thread(struct md_thread **threadp)
+void md_unregister_thread(struct md_thread __rcu **threadp)
{
- struct md_thread *thread;
+ struct md_thread *thread = rcu_dereference_protected(*threadp, true);

- /*
- * Locking ensures that mddev_unlock does not wake_up a
- * non-existent thread
- */
- spin_lock(&pers_lock);
- thread = *threadp;
- if (!thread) {
- spin_unlock(&pers_lock);
+ if (!thread)
return;
- }
- *threadp = NULL;
- spin_unlock(&pers_lock);
+
+ rcu_assign_pointer(*threadp, NULL);
+ synchronize_rcu();

pr_debug("interrupting MD-thread pid %d\n", task_pid_nr(thread->tsk));
kthread_stop(thread->tsk);
@@ -9210,9 +9206,8 @@ static void md_start_sync(struct work_struct *ws)
{
struct mddev *mddev = container_of(ws, struct mddev, del_work);

- mddev->sync_thread = md_register_thread(md_do_sync,
- mddev,
- "resync");
+ rcu_assign_pointer(mddev->sync_thread,
+ md_register_thread(md_do_sync, mddev, "resync"));
if (!mddev->sync_thread) {
pr_warn("%s: could not start resync thread...\n",
mdname(mddev));
diff --git a/drivers/md/md.h b/drivers/md/md.h
index e148e3c83b0d..324558c3fa06 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -367,8 +367,8 @@ struct mddev {
int new_chunk_sectors;
int reshape_backwards;

- struct md_thread *thread; /* management thread */
- struct md_thread *sync_thread; /* doing resync or reconstruct */
+ struct md_thread __rcu *thread; /* management thread */
+ struct md_thread __rcu *sync_thread; /* doing resync or reconstruct */

/* 'last_sync_action' is initialized to "none". It is set when a
* sync operation (i.e "data-check", "requested-resync", "resync",
@@ -734,8 +734,8 @@ extern struct md_thread *md_register_thread(
void (*run)(struct md_thread *thread),
struct mddev *mddev,
const char *name);
-extern void md_unregister_thread(struct md_thread **threadp);
-extern void md_wakeup_thread(struct md_thread *thread);
+extern void md_unregister_thread(struct md_thread __rcu **threadp);
+extern void md_wakeup_thread(struct md_thread __rcu *thread);
extern void md_check_recovery(struct mddev *mddev);
extern void md_reap_sync_thread(struct mddev *mddev);
extern int mddev_init_writes_pending(struct mddev *mddev);
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 68a9e2d9985b..2f1011ffdf09 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -3084,7 +3084,8 @@ static struct r1conf *setup_conf(struct mddev *mddev)
}

err = -ENOMEM;
- conf->thread = md_register_thread(raid1d, mddev, "raid1");
+ rcu_assign_pointer(conf->thread,
+ md_register_thread(raid1d, mddev, "raid1"));
if (!conf->thread)
goto abort;

@@ -3177,8 +3178,8 @@ static int raid1_run(struct mddev *mddev)
/*
* Ok, everything is just fine now
*/
- mddev->thread = conf->thread;
- conf->thread = NULL;
+ rcu_assign_pointer(mddev->thread, conf->thread);
+ rcu_assign_pointer(conf->thread, NULL);
mddev->private = conf;
set_bit(MD_FAILFAST_SUPPORTED, &mddev->flags);

diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index ebb6788820e7..468f189da7a0 100644
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -130,7 +130,7 @@ struct r1conf {
/* When taking over an array from a different personality, we store
* the new thread here until we fully activate the array.
*/
- struct md_thread *thread;
+ struct md_thread __rcu *thread;

/* Keep track of cluster resync window to send to other
* nodes.
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 6c66357f92f5..6590aa49598c 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -980,6 +980,7 @@ static void lower_barrier(struct r10conf *conf)
static bool stop_waiting_barrier(struct r10conf *conf)
{
struct bio_list *bio_list = current->bio_list;
+ struct md_thread *thread;

/* barrier is dropped */
if (!conf->barrier)
@@ -995,8 +996,11 @@ static bool stop_waiting_barrier(struct r10conf *conf)
(!bio_list_empty(&bio_list[0]) || !bio_list_empty(&bio_list[1])))
return true;

+ /* daemon thread must exist while handling io */
+ thread = rcu_dereference_protected(conf->mddev->thread, true);
+
/* move on if recovery thread is blocked by us */
- if (conf->mddev->thread->tsk == current &&
+ if (thread->tsk == current &&
test_bit(MD_RECOVERY_RUNNING, &conf->mddev->recovery) &&
conf->nr_queued > 0)
return true;
@@ -4078,7 +4082,8 @@ static struct r10conf *setup_conf(struct mddev *mddev)
atomic_set(&conf->nr_pending, 0);

err = -ENOMEM;
- conf->thread = md_register_thread(raid10d, mddev, "raid10");
+ rcu_assign_pointer(conf->thread,
+ md_register_thread(raid10d, mddev, "raid10"));
if (!conf->thread)
goto out;

@@ -4141,8 +4146,8 @@ static int raid10_run(struct mddev *mddev)
}
}

- mddev->thread = conf->thread;
- conf->thread = NULL;
+ rcu_assign_pointer(mddev->thread, conf->thread);
+ rcu_assign_pointer(conf->thread, NULL);

if (mddev->queue) {
blk_queue_max_write_zeroes_sectors(mddev->queue, 0);
@@ -4273,8 +4278,8 @@ static int raid10_run(struct mddev *mddev)
clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
- mddev->sync_thread = md_register_thread(md_do_sync, mddev,
- "reshape");
+ rcu_assign_pointer(mddev->sync_thread,
+ md_register_thread(md_do_sync, mddev, "reshape"));
if (!mddev->sync_thread)
goto out_free_conf;
}
@@ -4686,8 +4691,8 @@ static int raid10_start_reshape(struct mddev *mddev)
set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);

- mddev->sync_thread = md_register_thread(md_do_sync, mddev,
- "reshape");
+ rcu_assign_pointer(mddev->sync_thread,
+ md_register_thread(md_do_sync, mddev, "reshape"));
if (!mddev->sync_thread) {
ret = -EAGAIN;
goto abort;
diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h
index 8c072ce0bc54..63e48b11b552 100644
--- a/drivers/md/raid10.h
+++ b/drivers/md/raid10.h
@@ -100,7 +100,7 @@ struct r10conf {
/* When taking over an array from a different personality, we store
* the new thread here until we fully activate the array.
*/
- struct md_thread *thread;
+ struct md_thread __rcu *thread;

/*
* Keep track of cluster resync window to send to other nodes.
diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 46182b955aef..040f5d6e1298 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -120,7 +120,7 @@ struct r5l_log {
struct bio_set bs;
mempool_t meta_pool;

- struct md_thread *reclaim_thread;
+ struct md_thread __rcu *reclaim_thread;
unsigned long reclaim_target; /* number of space that need to be
* reclaimed. if it's 0, reclaim spaces
* used by io_units which are in
@@ -1576,17 +1576,18 @@ void r5l_wake_reclaim(struct r5l_log *log, sector_t space)

void r5l_quiesce(struct r5l_log *log, int quiesce)
{
- struct mddev *mddev;
+ struct mddev *mddev = log->rdev->mddev;
+ struct md_thread *thread = rcu_dereference_protected(
+ log->reclaim_thread, lockdep_is_held(&mddev->reconfig_mutex));

if (quiesce) {
/* make sure r5l_write_super_and_discard_space exits */
- mddev = log->rdev->mddev;
wake_up(&mddev->sb_wait);
- kthread_park(log->reclaim_thread->tsk);
+ kthread_park(thread->tsk);
r5l_wake_reclaim(log, MaxSector);
r5l_do_reclaim(log);
} else
- kthread_unpark(log->reclaim_thread->tsk);
+ kthread_unpark(thread->tsk);
}

bool r5l_log_disk_error(struct r5conf *conf)
@@ -3063,6 +3064,7 @@ void r5c_update_on_rdev_error(struct mddev *mddev, struct md_rdev *rdev)
int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
{
struct r5l_log *log;
+ struct md_thread *thread;
int ret;

pr_debug("md/raid:%s: using device %pg as journal\n",
@@ -3121,11 +3123,13 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
spin_lock_init(&log->tree_lock);
INIT_RADIX_TREE(&log->big_stripe_tree, GFP_NOWAIT | __GFP_NOWARN);

- log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
- log->rdev->mddev, "reclaim");
- if (!log->reclaim_thread)
+ thread = md_register_thread(r5l_reclaim_thread, log->rdev->mddev,
+ "reclaim");
+ if (!thread)
goto reclaim_thread;
- log->reclaim_thread->timeout = R5C_RECLAIM_WAKEUP_INTERVAL;
+
+ thread->timeout = R5C_RECLAIM_WAKEUP_INTERVAL;
+ rcu_assign_pointer(log->reclaim_thread, thread);

init_waitqueue_head(&log->iounit_wait);

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 7b820b81d8c2..1f68bba9d0b9 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7665,7 +7665,8 @@ static struct r5conf *setup_conf(struct mddev *mddev)
}

sprintf(pers_name, "raid%d", mddev->new_level);
- conf->thread = md_register_thread(raid5d, mddev, pers_name);
+ rcu_assign_pointer(conf->thread,
+ md_register_thread(raid5d, mddev, pers_name));
if (!conf->thread) {
pr_warn("md/raid:%s: couldn't allocate thread.\n",
mdname(mddev));
@@ -7889,8 +7890,8 @@ static int raid5_run(struct mddev *mddev)
}

conf->min_offset_diff = min_offset_diff;
- mddev->thread = conf->thread;
- conf->thread = NULL;
+ rcu_assign_pointer(mddev->thread, conf->thread);
+ rcu_assign_pointer(conf->thread, NULL);
mddev->private = conf;

for (i = 0; i < conf->raid_disks && conf->previous_raid_disks;
@@ -7989,8 +7990,8 @@ static int raid5_run(struct mddev *mddev)
clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
- mddev->sync_thread = md_register_thread(md_do_sync, mddev,
- "reshape");
+ rcu_assign_pointer(mddev->sync_thread,
+ md_register_thread(md_do_sync, mddev, "reshape"));
if (!mddev->sync_thread)
goto abort;
}
@@ -8567,8 +8568,8 @@ static int raid5_start_reshape(struct mddev *mddev)
clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
- mddev->sync_thread = md_register_thread(md_do_sync, mddev,
- "reshape");
+ rcu_assign_pointer(mddev->sync_thread,
+ md_register_thread(md_do_sync, mddev, "reshape"));
if (!mddev->sync_thread) {
mddev->recovery = 0;
spin_lock_irq(&conf->device_lock);
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index e873938a6125..f19707189a7b 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -679,7 +679,7 @@ struct r5conf {
/* When taking over an array from a different personality, we store
* the new thread here until we fully activate the array.
*/
- struct md_thread *thread;
+ struct md_thread __rcu *thread;
struct list_head temp_inactive_list[NR_STRIPE_HASH_LOCKS];
struct r5worker_group *worker_groups;
int group_cnt;
--
2.39.2