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Subject[PATCH] block: Fix use-after-free issue accessing struct io_cq
Date
There is a potential race between ioc_release_fn() and
ioc_clear_queue() as shown below, due to which below kernel
crash is observed. It also can result into use-after-free
issue.

context#1: context#2:
ioc_release_fn() __ioc_clear_queue() gets the same icq
->spin_lock(&ioc->lock); ->spin_lock(&ioc->lock);
->ioc_destroy_icq(icq);
->list_del_init(&icq->q_node);
->call_rcu(&icq->__rcu_head,
icq_free_icq_rcu);
->spin_unlock(&ioc->lock);
->ioc_destroy_icq(icq);
->hlist_del_init(&icq->ioc_node);
This results into below crash as this memory
is now used by icq->__rcu_head in context#1.
There is a chance that icq could be free'd
as well.

22150.386550: <6> Unable to handle kernel write to read-only memory
at virtual address ffffffaa8d31ca50
...
Call trace:
22150.607350: <2> ioc_destroy_icq+0x44/0x110
22150.611202: <2> ioc_clear_queue+0xac/0x148
22150.615056: <2> blk_cleanup_queue+0x11c/0x1a0
22150.619174: <2> __scsi_remove_device+0xdc/0x128
22150.623465: <2> scsi_forget_host+0x2c/0x78
22150.627315: <2> scsi_remove_host+0x7c/0x2a0
22150.631257: <2> usb_stor_disconnect+0x74/0xc8
22150.635371: <2> usb_unbind_interface+0xc8/0x278
22150.639665: <2> device_release_driver_internal+0x198/0x250
22150.644897: <2> device_release_driver+0x24/0x30
22150.649176: <2> bus_remove_device+0xec/0x140
22150.653204: <2> device_del+0x270/0x460
22150.656712: <2> usb_disable_device+0x120/0x390
22150.660918: <2> usb_disconnect+0xf4/0x2e0
22150.664684: <2> hub_event+0xd70/0x17e8
22150.668197: <2> process_one_work+0x210/0x480
22150.672222: <2> worker_thread+0x32c/0x4c8

Fix this by adding a new ICQ_DESTROYED flag in ioc_destroy_icq() to
indicate this icq is once marked as destroyed. Also, ensure
__ioc_clear_queue() 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: Sahitya Tummala <stummala@codeaurora.org>
Co-developed-by: Pradeep P V K <ppvk@codeaurora.org>
Signed-off-by: Pradeep P V K <ppvk@codeaurora.org>
---
block/blk-ioc.c | 7 +++++++
include/linux/iocontext.h | 1 +
2 files changed, 8 insertions(+)

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 5ed59ac..9df50fb 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -84,6 +84,7 @@ static void ioc_destroy_icq(struct io_cq *icq)
* making it impossible to determine icq_cache. Record it in @icq.
*/
icq->__rcu_icq_cache = et->icq_cache;
+ icq->flags |= ICQ_DESTROYED;
call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
}

@@ -212,15 +213,21 @@ static void __ioc_clear_queue(struct list_head *icq_list)
{
unsigned long flags;

+ rcu_read_lock();
while (!list_empty(icq_list)) {
struct io_cq *icq = list_entry(icq_list->next,
struct io_cq, q_node);
struct io_context *ioc = icq->ioc;

spin_lock_irqsave(&ioc->lock, flags);
+ if (icq->flags & ICQ_DESTROYED) {
+ spin_unlock_irqrestore(&ioc->lock, flags);
+ continue;
+ }
ioc_destroy_icq(icq);
spin_unlock_irqrestore(&ioc->lock, flags);
}
+ rcu_read_unlock();
}

/**
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index dba15ca..1dcd919 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -8,6 +8,7 @@

enum {
ICQ_EXITED = 1 << 2,
+ ICQ_DESTROYED = 1 << 3,
};

/*
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
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