There is a potential race between ioc_clear_fn() and
exit_io_context() as shown below, due to which below
crash is observed. It can also result into use-after-free
issue.
context#1: context#2:
ioc_release_fn() do_exit();
->spin_lock(&ioc->lock); ->exit_io_context();
->ioc_destroy_icq(icq); ->ioc_exit_icqs();
->list_del_init(&icq->q_node); ->spin_lock_irq(&ioc->lock);
->call_rcu(&icq->__rcu_head,
icq_free_icq_rcu);
->spin_unlock(&ioc->lock);
->ioc_exit_icq(); gets the same icq
->bfq_exit_icq();
This results into below crash as bic
is NULL as it is derived from icq.
There is a chance that icq could be
free'd as well.
[33.245722][ T8666] Unable to handle kernel NULL pointer dereference
at virtual address 0000000000000018.
...
Call trace:
[33.325782][ T8666] bfq_exit_icq+0x28/0xa8
[33.325785][ T8666] exit_io_context+0xcc/0x100
[33.325786][ T8666] do_exit+0x764/0xa58
[33.325791][ T8666] do_group_exit+0x0/0xa0
[33.325793][ T8666] invoke_syscall+0x48/0x114
[33.325802][ T8666] el0_svc_common+0xcc/0x118
[33.325805][ T8666] do_el0_svc+0x34/0xd0
[33.325807][ T8666] el0_svc+0x38/0xd0
[33.325812][ T8666] el0t_64_sync_handler+0x8c/0xfc
[33.325813][ T8666] el0t_64_sync+0x1a0/0x1a4
Fix this by checking with ICQ_DESTROYED flags in ioc_exit_icqs().
Also, ensure ioc_exit_icq() is accessing icq within rcu_read_lock/unlock
so that icq doesn't get free'd up while it is still using it.
Signed-off-by: Pradeep P V K <quic_pragalla@xxxxxxxxxxx>
---
block/blk-ioc.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 63fc02042408..1aa34fd46ac8 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -60,10 +60,14 @@ static void ioc_exit_icqs(struct io_context *ioc)
{
struct io_cq *icq;
+ rcu_read_lock();
spin_lock_irq(&ioc->lock);
- hlist_for_each_entry(icq, &ioc->icq_list, ioc_node)
- ioc_exit_icq(icq);
+ hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {
+ if (!(icq->flags & ICQ_DESTROYED))
+ ioc_exit_icq(icq);
+ }
spin_unlock_irq(&ioc->lock);
+ rcu_read_unlock();
}
/*
--
2.17.1
