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SubjectRe: Use after free bug in null_blk driver
From
2015-07-19 2:19 GMT+09:00 Mike Krinkin <krinkin.m.u@gmail.com>:
> On Sun, Jul 19, 2015 at 01:18:44AM +0900, Akinobu Mita wrote:
>> 2015-07-18 23:51 GMT+09:00 Mike Krinkin <krinkin.m.u@gmail.com>:
>> > Hi,
>> >
>> > i noticed that loading null_blk with queue_mode=1 and irqmode=2 parameters
>> > and slab poisoning enabled causes general protection fault:
>> >
>> > [ 20.671974] general protection fault: 0000 [#1] SMP
>> > [ 20.678050] Modules linked in: null_blk(+) usbhid hid psmouse floppy
>> > [ 20.688351] CPU: 0 PID: 147 Comm: modprobe Not tainted 4.2.0-rc2+ #76
>> > [ 20.695961] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> > [ 20.705143] task: ffff88007f2ed100 ti: ffff88007f0a4000 task.ti: ffff88007f0a4000
>> > [ 20.715511] RIP: 0010:[<ffffffffa0028152>] [<ffffffffa0028152>] null_cmd_timer_expired+0x62/0xc0 [null_blk]
>> > [ 20.730541] RSP: 0018:ffff88007d203e78 EFLAGS: 00010082
>> > [ 20.737301] RAX: ffff88007ec16b80 RBX: 6b6b6b6b6b6b6b6b RCX: 0000000000000000
>> > [ 20.747034] RDX: ffff88007f260888 RSI: 0000000000000000 RDI: ffff88007f260850
>> > [ 20.762601] RBP: ffff88007d203e98 R08: 0000000000000001 R09: 0000000000000000
>> > [ 20.771472] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
>> > [ 20.782522] R13: ffff88007d218780 R14: 0000000000000000 R15: ffff88007d20fba8
>> > [ 20.792347] FS: 00007f02e1500740(0000) GS:ffff88007d200000(0000) knlGS:0000000000000000
>> > [ 20.805319] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> > [ 20.813120] CR2: 00007ffd52478dd8 CR3: 000000007f3dd000 CR4: 00000000000007f0
>> > [ 20.825357] Stack:
>> > [ 20.827764] ffff88007d218788 ffff88007d20fa00 ffff88007d20fac0 ffffffffa00280f0
>> > [ 20.838269] ffff88007d203f08 ffffffff810f822b 000000045dd35ed6 ffff88007d20fa18
>> > [ 20.853377] 00000001810f89e7 ffff88007d20fa00 ffff88007d20fb28 000000045dd35ed6
>> > [ 20.863415] Call Trace:
>> > [ 20.866398] <IRQ>
>> > [ 20.869088] [<ffffffffa00280f0>] ? null_softirq_done_fn+0x30/0x30 [null_blk]
>> > [ 20.880219] [<ffffffff810f822b>] __hrtimer_run_queues+0x11b/0x6e0
>> > [ 20.891048] [<ffffffff810f8a0b>] hrtimer_interrupt+0xab/0x1b0
>> > [ 20.899542] [<ffffffff810511ec>] local_apic_timer_interrupt+0x3c/0x70
>> > [ 20.911730] [<ffffffff817c8d21>] smp_apic_timer_interrupt+0x41/0x60
>> > [ 20.921854] [<ffffffff817c6e50>] apic_timer_interrupt+0x70/0x80
>> > [ 20.931084] <EOI>
>> > [ 20.933406] [<ffffffff817c55ab>] ? _raw_spin_unlock_irqrestore+0x3b/0x60
>> > [ 20.945250] [<ffffffff810f7a47>] hrtimer_start_range_ns+0x1a7/0x540
>> > [ 20.955952] [<ffffffff810d2d41>] ? trace_hardirqs_on_caller+0x151/0x1e0
>> > [ 20.963974] [<ffffffffa0028643>] null_request_fn+0xd3/0x100 [null_blk]
>> > [ 20.977159] [<ffffffff81391947>] __blk_run_queue+0x37/0x50
>> > [ 20.983782] [<ffffffff8139042d>] __elv_add_request+0x15d/0x440
>> > [ 20.991540] [<ffffffff81398e65>] blk_queue_bio+0x415/0x520
>> > [ 20.998876] [<ffffffff8139633c>] generic_make_request+0xcc/0x110
>> > [ 21.007095] [<ffffffff813963e7>] submit_bio+0x67/0x150
>> > [ 21.013603] [<ffffffff8125510c>] submit_bh_wbc+0x14c/0x180
>> > [ 21.019730] [<ffffffff81255560>] block_read_full_page+0x2b0/0x3a0
>> > [ 21.028023] [<ffffffff81257a90>] ? I_BDEV+0x20/0x20
>> > [ 21.034575] [<ffffffff81258420>] ? blkdev_readpages+0x20/0x20
>> > [ 21.040947] [<ffffffff81258438>] blkdev_readpage+0x18/0x20
>> > [ 21.048237] [<ffffffff8119875d>] do_read_cache_page+0x7d/0x1a0
>> > [ 21.056016] [<ffffffff8119889c>] read_cache_page+0x1c/0x20
>> > [ 21.063300] [<ffffffff813aaf50>] read_dev_sector+0x30/0x90
>> > [ 21.069804] [<ffffffff813acd40>] ? check_partition+0x1f0/0x1f0
>> > [ 21.076932] [<ffffffff813acd82>] adfspart_check_ICS+0x42/0x250
>> > [ 21.084317] [<ffffffff813d3804>] ? snprintf+0x34/0x40
>> > [ 21.090670] [<ffffffff813acd40>] ? check_partition+0x1f0/0x1f0
>> > [ 21.097864] [<ffffffff813acc50>] check_partition+0x100/0x1f0
>> > [ 21.104535] [<ffffffff813abba8>] rescan_partitions+0xa8/0x2b0
>> > [ 21.112087] [<ffffffff81259643>] __blkdev_get+0x313/0x460
>> > [ 21.120037] [<ffffffff812597d1>] blkdev_get+0x41/0x3a0
>> > [ 21.126266] [<ffffffff8123429d>] ? unlock_new_inode+0x5d/0x90
>> > [ 21.134043] [<ffffffff812582e0>] ? bdget+0x130/0x150
>> > [ 21.140369] [<ffffffff813a83dd>] ? disk_get_part+0xd/0x1d0
>> > [ 21.147357] [<ffffffff813a9526>] add_disk+0x436/0x4d0
>> > [ 21.153846] [<ffffffff813d38b0>] ? sprintf+0x40/0x50
>> > [ 21.159867] [<ffffffffa004e38e>] null_init+0x38e/0x1000 [null_blk]
>> > [ 21.167691] [<ffffffffa004e000>] ? 0xffffffffa004e000
>> > [ 21.174266] [<ffffffff81002123>] do_one_initcall+0xb3/0x1e0
>> > [ 21.182276] [<ffffffff811f2fcf>] ? kmem_cache_alloc_trace+0x36f/0x3b0
>> > [ 21.190291] [<ffffffff817ba7fb>] do_init_module+0x61/0x1ec
>> > [ 21.197112] [<ffffffff81115a8e>] load_module+0x24fe/0x2810
>> > [ 21.204237] [<ffffffff81110fc0>] ? m_show+0x1a0/0x1a0
>> > [ 21.213498] [<ffffffff81115fa0>] SyS_finit_module+0x80/0xb0
>> > [ 21.221360] [<ffffffff817c5f32>] entry_SYSCALL_64_fastpath+0x16/0x7a
>> > [ 21.230181] Code: e8 24 40 3b e1 48 89 c3 eb 08 4d 85 e4 4c 89 e3 74 e2 48 8d 7b f0 4c 8b 23 e8 db fe ff ff 48 8b 43 28 48 85 c0 74 e3 48 8b 58 30 <48> 83 bb 38 01 00 00 00 75 d5 48 8b 83 98 08 00 00 a8 04 74 ca
>> > [ 21.281572] RIP [<ffffffffa0028152>] null_cmd_timer_expired+0x62/0xc0 [null_blk]
>> > [ 21.289770] RSP <ffff88007d203e78>
>> > [ 21.294601] ---[ end trace cd40ca6c9001dd7e ]---
>> > [ 21.299719] Kernel panic - not syncing: Fatal exception in interrupt
>> > [ 21.309176] Kernel Offset: disabled
>> > [ 21.312773] ---[ end Kernel panic - not syncing: Fatal exception in interrupt
>> >
>> > I suppose, it was introduced in commit 8b70f45e2eb2 ("null_blk: restart request
>> > processing on completion handler") by Akinobu Mita <akinobu.mita@gmail.com>. The
>>
>> Right. That commit introduced use-after-free bug.
>>
>> > following fix solves problem for me:
>> >
>> > diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
>> > index 69de41a..910f354 100644
>> > --- a/drivers/block/null_blk.c
>> > +++ b/drivers/block/null_blk.c
>> > @@ -242,7 +242,6 @@ static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer)
>> > do {
>> > cmd = container_of(entry, struct nullb_cmd, ll_list);
>> > entry = entry->next;
>> > - end_cmd(cmd);
>> >
>> > if (cmd->rq) {
>> > struct request_queue *q = cmd->rq->q;
>> > @@ -254,6 +253,7 @@ static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer)
>> > spin_unlock(q->queue_lock);
>> > }
>> > }
>> > + end_cmd(cmd);
>> > } while (entry);
>> > }
>>
>> But this change re-introduces the problem which I was trying to fix
>> in the commit 8b70f45e2eb2. We need to call end_cmd() before
>> blk_start_queue(). So the corrct fix should save cmd->rq->q to
>> local variable before end_cmd() and call blk_start_queue() with
>> the saved value.
>
> Yes, you are right, correct fix looks something like this:
>
> diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
> index 69de41a..3177b24 100644
> --- a/drivers/block/null_blk.c
> +++ b/drivers/block/null_blk.c
> @@ -240,19 +240,19 @@ static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer)
> while ((entry = llist_del_all(&cq->list)) != NULL) {
> entry = llist_reverse_order(entry);
> do {
> + struct request_queue *q = NULL;
> +
> cmd = container_of(entry, struct nullb_cmd, ll_list);
> entry = entry->next;
> + if (cmd->rq)
> + q = cmd->rq->q;
> end_cmd(cmd);
>
> - if (cmd->rq) {
> - struct request_queue *q = cmd->rq->q;
> -
> - if (!q->mq_ops && blk_queue_stopped(q)) {
> - spin_lock(q->queue_lock);
> - if (blk_queue_stopped(q))
> - blk_start_queue(q);
> - spin_unlock(q->queue_lock);
> - }
> + if (q && !q->mq_ops && blk_queue_stopped(q)) {
> + spin_lock(q->queue_lock);
> + if (blk_queue_stopped(q))
> + blk_start_queue(q);
> + spin_unlock(q->queue_lock);
> }
> } while (entry);
> }
>

Looks good to me.

> But anyway, will you send a patch or should i submit a patch with this fix?

I think you should.

I have tested this patch and it works fine. So please add the following tag
when you submit this patch.

Tested-by: Akinobu Mita <akinobu.mita@gmail.com>


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