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Date: Tue, 21 Dec 2021 19:38:49 +0800
From: Yu Kuai <yukuai3@...wei.com>
To: <jack@...e.cz>, <gregkh@...uxfoundation.org>,
<paolo.valente@...aro.org>, <axboe@...nel.dk>
CC: <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<yukuai3@...wei.com>, <yi.zhang@...wei.com>
Subject: [PATCH linux-4.19.y 5/5] block, bfq: fix use after free in bfq_bfqq_expire
From: Paolo Valente <paolo.valente@...aro.org>
commit eed47d19d9362bdd958e4ab56af480b9dbf6b2b6 upstream.
The function bfq_bfqq_expire() invokes the function
__bfq_bfqq_expire(), and the latter may free the in-service bfq-queue.
If this happens, then no other instruction of bfq_bfqq_expire() must
be executed, or a use-after-free will occur.
Basing on the assumption that __bfq_bfqq_expire() invokes
bfq_put_queue() on the in-service bfq-queue exactly once, the queue is
assumed to be freed if its refcounter is equal to one right before
invoking __bfq_bfqq_expire().
But, since commit 9dee8b3b057e ("block, bfq: fix queue removal from
weights tree") this assumption is false. __bfq_bfqq_expire() may also
invoke bfq_weights_tree_remove() and, since commit 9dee8b3b057e
("block, bfq: fix queue removal from weights tree"), also
the latter function may invoke bfq_put_queue(). So __bfq_bfqq_expire()
may invoke bfq_put_queue() twice, and this is the actual case where
the in-service queue may happen to be freed.
To address this issue, this commit moves the check on the refcounter
of the queue right around the last bfq_put_queue() that may be invoked
on the queue.
Fixes: 9dee8b3b057e ("block, bfq: fix queue removal from weights tree")
Reported-by: Dmitrii Tcvetkov <demfloro@...floro.ru>
Reported-by: Douglas Anderson <dianders@...omium.org>
Tested-by: Dmitrii Tcvetkov <demfloro@...floro.ru>
Tested-by: Douglas Anderson <dianders@...omium.org>
Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
block/bfq-iosched.c | 15 +++++++--------
block/bfq-iosched.h | 2 +-
block/bfq-wf2q.c | 17 +++++++++++++++--
3 files changed, 23 insertions(+), 11 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index d22452fa2d5a..c2529dfda3e5 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2816,7 +2816,7 @@ static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
bfq_remove_request(q, rq);
}
-static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq)
+static bool __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
/*
* If this bfqq is shared between multiple processes, check
@@ -2849,9 +2849,11 @@ static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq)
/*
* All in-service entities must have been properly deactivated
* or requeued before executing the next function, which
- * resets all in-service entites as no more in service.
+ * resets all in-service entities as no more in service. This
+ * may cause bfqq to be freed. If this happens, the next
+ * function returns true.
*/
- __bfq_bfqd_reset_in_service(bfqd);
+ return __bfq_bfqd_reset_in_service(bfqd);
}
/**
@@ -3256,7 +3258,6 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
bool slow;
unsigned long delta = 0;
struct bfq_entity *entity = &bfqq->entity;
- int ref;
/*
* Check whether the process is slow (see bfq_bfqq_is_slow).
@@ -3325,10 +3326,8 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
* reason.
*/
__bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
- ref = bfqq->ref;
- __bfq_bfqq_expire(bfqd, bfqq);
-
- if (ref == 1) /* bfqq is gone, no more actions on it */
+ if (__bfq_bfqq_expire(bfqd, bfqq))
+ /* bfqq is gone, no more actions on it */
return;
bfqq->injected_service = 0;
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 746bd570b85a..ca98c98a8179 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -993,7 +993,7 @@ bool __bfq_deactivate_entity(struct bfq_entity *entity,
bool ins_into_idle_tree);
bool next_queue_may_preempt(struct bfq_data *bfqd);
struct bfq_queue *bfq_get_next_queue(struct bfq_data *bfqd);
-void __bfq_bfqd_reset_in_service(struct bfq_data *bfqd);
+bool __bfq_bfqd_reset_in_service(struct bfq_data *bfqd);
void bfq_deactivate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bool ins_into_idle_tree, bool expiration);
void bfq_activate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq);
diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index 1301289b14aa..11ff5ceae02b 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -1600,7 +1600,8 @@ struct bfq_queue *bfq_get_next_queue(struct bfq_data *bfqd)
return bfqq;
}
-void __bfq_bfqd_reset_in_service(struct bfq_data *bfqd)
+/* returns true if the in-service queue gets freed */
+bool __bfq_bfqd_reset_in_service(struct bfq_data *bfqd)
{
struct bfq_queue *in_serv_bfqq = bfqd->in_service_queue;
struct bfq_entity *in_serv_entity = &in_serv_bfqq->entity;
@@ -1624,8 +1625,20 @@ void __bfq_bfqd_reset_in_service(struct bfq_data *bfqd)
* service tree either, then release the service reference to
* the queue it represents (taken with bfq_get_entity).
*/
- if (!in_serv_entity->on_st)
+ if (!in_serv_entity->on_st) {
+ /*
+ * If no process is referencing in_serv_bfqq any
+ * longer, then the service reference may be the only
+ * reference to the queue. If this is the case, then
+ * bfqq gets freed here.
+ */
+ int ref = in_serv_bfqq->ref;
bfq_put_queue(in_serv_bfqq);
+ if (ref == 1)
+ return true;
+ }
+
+ return false;
}
void bfq_deactivate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
--
2.31.1
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