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block, bfq: fix use after free in bfq_bfqq_expire

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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 9dee8b3b05 ("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 9dee8b3b05
("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: 9dee8b3b05 ("block, bfq: fix queue removal from weights tree")
Reported-by: Dmitrii Tcvetkov <demfloro@demfloro.ru>
Reported-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Dmitrii Tcvetkov <demfloro@demfloro.ru>
Tested-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Paolo Valente 2019-04-10 10:38:33 +02:00 committed by Jens Axboe
parent 3ec482d15c
commit eed47d19d9
3 changed files with 23 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
block/bfq-iosched.c
View File

@ -2822,7 +2822,7 @@ 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
@ -2855,9 +2855,11 @@ 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);
}
/**
@ -3262,7 +3264,6 @@ 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).
@ -3347,10 +3348,8 @@ 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;

2
block/bfq-iosched.h
View File

@ -995,7 +995,7 @@ 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);

17
block/bfq-wf2q.c
View File

@ -1605,7 +1605,8 @@ 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;
@ -1629,8 +1630,20 @@ 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,