答复: [PATCH -next v3] bfq: fix use-after-free in bfq_dispatch_request

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Hi paolo:
	Thanks for your question, it is my negligence.
	I have two ideas for repairing the problem:

1. use ref++ to avoid the in_serv_queue being released. Patch as follow:

block/bfq-iosched.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index fec18118dc30..70bd280170f9 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5066,6 +5066,7 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
        spin_lock_irq(&bfqd->lock);

        in_serv_queue = bfqd->in_service_queue;
+       in_serv_queue->ref++; /* aviod in_serv_queue release */
        waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue);

        rq = __bfq_dispatch_request(hctx);
@@ -5077,6 +5078,10 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)

        bfq_update_dispatch_stats(hctx->queue, rq, in_serv_queue,
                                  idle_timer_disabled);
+       /* resume in_serv_queue */
+       spin_lock_irq(&bfqd->lock);
+       bfq_put_queue(in_serv_queue);
+       spin_unlock_irq(&bfqd->lock);

        return rq;
 }

2. add new changes to previous, taking out bfqq_group(in_serv_queue) from bfq_update_dispatch_stats. Patch as follow:

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5007,7 +5007,7 @@ static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
 #ifdef CONFIG_BFQ_CGROUP_DEBUG
 static void bfq_update_dispatch_stats(struct request_queue *q,
                                      struct request *rq,
-                                     struct bfq_queue *in_serv_queue,
+                                     struct bfq_group *bfqg_in_serv,
                                      bool idle_timer_disabled)
 {
        struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL;
@@ -5039,7 +5039,7 @@ static void bfq_update_dispatch_stats(struct request_queue *q,
                 * therefore guaranteed to exist because of the above
                 * arguments.
                 */
-               bfqg_stats_update_idle_time(bfqq_group(in_serv_queue));
+               bfqg_stats_update_idle_time(bfqg_in_serv);
        if (bfqq) {
                struct bfq_group *bfqg = bfqq_group(bfqq);
 
@@ -5052,7 +5052,7 @@ static void bfq_update_dispatch_stats(struct request_queue *q,
 #else
 static inline void bfq_update_dispatch_stats(struct request_queue *q,
                                             struct request *rq,
-                                            struct bfq_queue *in_serv_queue,
+                                            struct bfq_group *bfqg_in_serv,
                                             bool idle_timer_disabled) {}
 #endif /* CONFIG_BFQ_CGROUP_DEBUG */
 
@@ -5062,20 +5062,23 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
        struct request *rq;
        struct bfq_queue *in_serv_queue;
        bool waiting_rq, idle_timer_disabled;
+       struct bfq_group *bfqg_in_serv;
 
        spin_lock_irq(&bfqd->lock);
 
        in_serv_queue = bfqd->in_service_queue;
        waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue);
+       bfqg_in_serv = bfqq_group(in_serv_queue);
 
        rq = __bfq_dispatch_request(hctx);
 
-       idle_timer_disabled =
-               waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
-
+       if (in_serv_queue == bfqd->in_service_queue) {
+               idle_timer_disabled =
+                       waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
+       }
        spin_unlock_irq(&bfqd->lock);
 
-       bfq_update_dispatch_stats(hctx->queue, rq, in_serv_queue,
+       bfq_update_dispatch_stats(hctx->queue, rq, bfqg_in_serv,
                                  idle_timer_disabled);
 
        return rq;

	what do you think?
	
	Thanks
	Zhang Wensheng
-----邮件原件-----
发件人: Paolo Valente [mailto:paolo.valente@xxxxxxxxxx] 
发送时间: 2021年12月17日 0:28
收件人: zhangwensheng (E) <zhangwensheng5@xxxxxxxxxx>
抄送: Jens Axboe <axboe@xxxxxxxxx>; linux-block@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
主题: Re: [PATCH -next v3] bfq: fix use-after-free in bfq_dispatch_request



> Il giorno 16 dic 2021, alle ore 13:21, Zhang Wensheng <zhangwensheng5@xxxxxxxxxx> ha scritto:
> 
> KASAN reports a use-after-free report when doing normal scsi-mq test
> 
> [69832.239032] 
> ==================================================================
> [69832.241810] BUG: KASAN: use-after-free in 
> bfq_dispatch_request+0x1045/0x44b0
> [69832.243267] Read of size 8 at addr ffff88802622ba88 by task 
> kworker/3:1H/155 [69832.244656] [69832.245007] CPU: 3 PID: 155 Comm: 
> kworker/3:1H Not tainted 5.10.0-10295-g576c6382529e #8 [69832.246626] 
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
> rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 [69832.249069] 
> Workqueue: kblockd blk_mq_run_work_fn [69832.250022] Call Trace:
> [69832.250541]  dump_stack+0x9b/0xce
> [69832.251232]  ? bfq_dispatch_request+0x1045/0x44b0
> [69832.252243]  print_address_description.constprop.6+0x3e/0x60
> [69832.253381]  ? __cpuidle_text_end+0x5/0x5 [69832.254211]  ? 
> vprintk_func+0x6b/0x120 [69832.254994]  ? 
> bfq_dispatch_request+0x1045/0x44b0
> [69832.255952]  ? bfq_dispatch_request+0x1045/0x44b0
> [69832.256914]  kasan_report.cold.9+0x22/0x3a [69832.257753]  ? 
> bfq_dispatch_request+0x1045/0x44b0
> [69832.258755]  check_memory_region+0x1c1/0x1e0 [69832.260248]  
> bfq_dispatch_request+0x1045/0x44b0
> [69832.261181]  ? bfq_bfqq_expire+0x2440/0x2440 [69832.262032]  ? 
> blk_mq_delay_run_hw_queues+0xf9/0x170
> [69832.263022]  __blk_mq_do_dispatch_sched+0x52f/0x830
> [69832.264011]  ? blk_mq_sched_request_inserted+0x100/0x100
> [69832.265101]  __blk_mq_sched_dispatch_requests+0x398/0x4f0
> [69832.266206]  ? blk_mq_do_dispatch_ctx+0x570/0x570
> [69832.267147]  ? __switch_to+0x5f4/0xee0 [69832.267898]  
> blk_mq_sched_dispatch_requests+0xdf/0x140
> [69832.268946]  __blk_mq_run_hw_queue+0xc0/0x270 [69832.269840]  
> blk_mq_run_work_fn+0x51/0x60 [69832.278170]  
> process_one_work+0x6d4/0xfe0 [69832.278984]  worker_thread+0x91/0xc80 
> [69832.279726]  ? __kthread_parkme+0xb0/0x110 [69832.280554]  ? 
> process_one_work+0xfe0/0xfe0 [69832.281414]  kthread+0x32d/0x3f0 
> [69832.282082]  ? kthread_park+0x170/0x170 [69832.282849]  
> ret_from_fork+0x1f/0x30 [69832.283573] [69832.283886] Allocated by 
> task 7725:
> [69832.284599]  kasan_save_stack+0x19/0x40 [69832.285385]  
> __kasan_kmalloc.constprop.2+0xc1/0xd0
> [69832.286350]  kmem_cache_alloc_node+0x13f/0x460 [69832.287237]  
> bfq_get_queue+0x3d4/0x1140 [69832.287993]  
> bfq_get_bfqq_handle_split+0x103/0x510
> [69832.289015]  bfq_init_rq+0x337/0x2d50 [69832.289749]  
> bfq_insert_requests+0x304/0x4e10 [69832.290634]  
> blk_mq_sched_insert_requests+0x13e/0x390
> [69832.291629]  blk_mq_flush_plug_list+0x4b4/0x760
> [69832.292538]  blk_flush_plug_list+0x2c5/0x480 [69832.293392]  
> io_schedule_prepare+0xb2/0xd0 [69832.294209]  
> io_schedule_timeout+0x13/0x80 [69832.295014]  
> wait_for_common_io.constprop.1+0x13c/0x270
> [69832.296137]  submit_bio_wait+0x103/0x1a0 [69832.296932]  
> blkdev_issue_discard+0xe6/0x160 [69832.297794]  
> blk_ioctl_discard+0x219/0x290 [69832.298614]  
> blkdev_common_ioctl+0x50a/0x1750 [69832.304715]  
> blkdev_ioctl+0x470/0x600 [69832.305474]  block_ioctl+0xde/0x120 
> [69832.306232]  vfs_ioctl+0x6c/0xc0 [69832.306877]  
> __se_sys_ioctl+0x90/0xa0 [69832.307629]  do_syscall_64+0x2d/0x40 
> [69832.308362]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [69832.309382]
> [69832.309701] Freed by task 155:
> [69832.310328]  kasan_save_stack+0x19/0x40 [69832.311121]  
> kasan_set_track+0x1c/0x30 [69832.311868]  
> kasan_set_free_info+0x1b/0x30 [69832.312699]  
> __kasan_slab_free+0x111/0x160 [69832.313524]  
> kmem_cache_free+0x94/0x460 [69832.314367]  bfq_put_queue+0x582/0x940 
> [69832.315112]  __bfq_bfqd_reset_in_service+0x166/0x1d0
> [69832.317275]  bfq_bfqq_expire+0xb27/0x2440 [69832.318084]  
> bfq_dispatch_request+0x697/0x44b0 [69832.318991]  
> __blk_mq_do_dispatch_sched+0x52f/0x830
> [69832.319984]  __blk_mq_sched_dispatch_requests+0x398/0x4f0
> [69832.321087]  blk_mq_sched_dispatch_requests+0xdf/0x140
> [69832.322225]  __blk_mq_run_hw_queue+0xc0/0x270 [69832.323114]  
> blk_mq_run_work_fn+0x51/0x60 [69832.323942]  
> process_one_work+0x6d4/0xfe0 [69832.324772]  worker_thread+0x91/0xc80 
> [69832.325518]  kthread+0x32d/0x3f0 [69832.326205]  
> ret_from_fork+0x1f/0x30 [69832.326932] [69832.338297] The buggy 
> address belongs to the object at ffff88802622b968 [69832.338297]  
> which belongs to the cache bfq_queue of size 512 [69832.340766] The 
> buggy address is located 288 bytes inside of [69832.340766]  512-byte 
> region [ffff88802622b968, ffff88802622bb68) [69832.343091] The buggy 
> address belongs to the page:
> [69832.344097] page:ffffea0000988a00 refcount:1 mapcount:0 
> mapping:0000000000000000 index:0xffff88802622a528 pfn:0x26228 
> [69832.346214] head:ffffea0000988a00 order:2 compound_mapcount:0 
> compound_pincount:0 [69832.347719] flags: 0x1fffff80010200(slab|head) 
> [69832.348625] raw: 001fffff80010200 ffffea0000dbac08 ffff888017a57650 
> ffff8880179fe840 [69832.354972] raw: ffff88802622a528 0000000000120008 
> 00000001ffffffff 0000000000000000 [69832.356547] page dumped because: 
> kasan: bad access detected [69832.357652] [69832.357970] Memory state around the buggy address:
> [69832.358926]  ffff88802622b980: fb fb fb fb fb fb fb fb fb fb fb fb 
> fb fb fb fb [69832.360358]  ffff88802622ba00: fb fb fb fb fb fb fb fb 
> fb fb fb fb fb fb fb fb [69832.361810] >ffff88802622ba80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [69832.363273]                       ^
> [69832.363975]  ffff88802622bb00: fb fb fb fb fb fb fb fb fb fb fb fb 
> fb fc fc fc [69832.375960]  ffff88802622bb80: fc fc fc fc fc fc fc fc 
> fc fc fc fc fc fc fc fc [69832.377405] 
> ==================================================================
> 
> In bfq_dispatch_requestfunction, it may have function call:
> 
> bfq_dispatch_request
> 	__bfq_dispatch_request
> 		bfq_select_queue
> 			bfq_bfqq_expire
> 				__bfq_bfqd_reset_in_service
> 					bfq_put_queue
> 						kmem_cache_free
> In this function call, in_serv_queue has beed expired and meet the 
> conditions to free. In the function bfq_dispatch_request, the address 
> of in_serv_queue pointing to has been released. For getting the value 
> of idle_timer_disabled, it will get flags value from the address which 
> in_serv_queue pointing to, then the problem of use-after-free happens;
> 
> Fix the problem by check in_serv_queue == bfqd->in_service_queue, to 
> get the value of idle_timer_disabled if in_serve_queue is equel to 
> bfqd->in_service_queue. If the space of in_serv_queue pointing has 
> been released, this judge will aviod use-after-free problem.
> And if in_serv_queue may be expired but it still exists, this judge 
> may have little effects on the function bfqg_stats_update_idle_time in 
> bfq_update_dispatch_stats.
> 
> Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> Signed-off-by: Zhang Wensheng <zhangwensheng5@xxxxxxxxxx>
> ---
> block/bfq-iosched.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 
> fec18118dc30..97533634b99e 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -5061,7 +5061,7 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
> 	struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
> 	struct request *rq;
> 	struct bfq_queue *in_serv_queue;
> -	bool waiting_rq, idle_timer_disabled;
> +	bool waiting_rq, idle_timer_disabled = false;
> 
> 	spin_lock_irq(&bfqd->lock);
> 
> @@ -5070,9 +5070,10 @@ static struct request 
> *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
> 
> 	rq = __bfq_dispatch_request(hctx);
> 
> -	idle_timer_disabled =
> -		waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
> -
> +	if (in_serv_queue == bfqd->in_service_queue) {
> +		idle_timer_disabled =
> +			waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
> +	}

Good catch!

> 	spin_unlock_irq(&bfqd->lock);
> 
> 	bfq_update_dispatch_stats(hctx->queue, rq, in_serv_queue,

Yet, what about the above use of in_serv_queue then?

Thanks,
Paolo

> --
> 2.31.1
> 





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