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Message-ID: <de0621ea-a7f4-bbb2-1560-7cf4f65d651c@gmail.com>
Date: Thu, 16 Sep 2021 13:56:11 +0300
From: Pavel Skripkin <paskripkin@...il.com>
To: Joel Stanley <joel@....id.au>, Sasha Levin <sashal@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Hillf Danton <hdanton@...a.com>,
syzbot <syzbot+9937dc42271cd87d4b98@...kaller.appspotmail.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
syzkaller-bugs@...glegroups.com, Eric Sandeen <sandeen@...hat.com>,
Al Viro <viro@...iv.linux.org.uk>,
Luis Chamberlain <mcgrof@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [syzbot] WARNING in internal_create_group
On 9/16/21 09:55, Joel Stanley wrote:
> On Wed, 11 Aug 2021 at 21:39, Pavel Skripkin <paskripkin@...il.com> wrote:
>>
>> On 7/21/21 7:30 AM, Christoph Hellwig wrote:
>> > On Wed, Jul 21, 2021 at 11:37:03AM +0800, Hillf Danton wrote:
>> >> On Tue, 20 Jul 2021 11:53:27 -0700
>> >> >syzbot has found a reproducer for the following issue on:
>> >> >
>> >> >HEAD commit: 8cae8cd89f05 seq_file: disallow extremely large seq buffer..
>> >> >git tree: upstream
>> >> >console output: https://syzkaller.appspot.com/x/log.txt?x=116f92ec300000
>> >> >kernel config: https://syzkaller.appspot.com/x/.config?x=7273c75708b55890
>> >> >dashboard link: https://syzkaller.appspot.com/bug?extid=9937dc42271cd87d4b98
>> >> >syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15fc287c300000
>> >> >C reproducer: https://syzkaller.appspot.com/x/repro.c?x=178cbf6a300000
>> >
>> > <snip>
>> >
>> >> >WARNING: CPU: 0 PID: 8435 at fs/sysfs/group.c:116 internal_create_group+0x911/0xb20 fs/sysfs/group.c:116
>> >
>> > <snip>
>> >
>> >> The device_add(ddev) in register_disk() may fail but it proceeds to register
>> >> block queue even at the failure ... this falls in the class of known issue
>> >> given the comment line.
>> >>
>> >> * FIXME: error handling
>> >> */
>> >> static void __device_add_disk(struct device *parent, struct gendisk *disk,
>> >
>> > Yes, Luis is working on actually fixing this - but it requires changes
>> > to every single block driver. How does a cap on the seq_buf size
>> > propagate here, though?
>> >
>>
>> Hi!
>>
>> I've looked into this, and, I think, we can add sanity check for
>> first_minor. If user will pass too big index (syzbot's repro passes
>> 1048576) this value will be shifted to part_shift and then truncated to
>> byte in __device_add_disk() and assigned to dev->devt. User may be
>> confused about why he passed 1048576, but sysfs warns about duplicate
>> creation of /dev/block/43:0
>>
>> So, these type of errors can be handled before passing wrong values to
>> sysfs API like this:
>>
>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>> index c38317979f74..600e9bab5d43 100644
>> --- a/drivers/block/nbd.c
>> +++ b/drivers/block/nbd.c
>> @@ -1725,7 +1725,17 @@ static int nbd_dev_add(int index)
>> refcount_set(&nbd->refs, 1);
>> INIT_LIST_HEAD(&nbd->list);
>> disk->major = NBD_MAJOR;
>> +
>> + /* Too big first_minor can cause duplicate creation of
>> + * sysfs files/links, since first_minor will be truncated to
>> + * byte in __device_add_disk().
>> + */
>> disk->first_minor = index << part_shift;
>> + if (disk->first_minor > 0xff) {
>> + err = -EINVAL;
>> + goto out_free_idr;
>> + }
>> +
>> disk->minors = 1 << part_shift;
>> disk->fops = &nbd_fops;
>> disk->private_data = nbd;
>>
>
> This one got backported to v5.10.65, and causes a warning on boot:
>
> [ 7.114976] ------------[ cut here ]------------
> [ 7.116811] WARNING: CPU: 0 PID: 1 at block/blk-mq.c:3045
> blk_mq_release+0x84/0x114
> [ 7.117510] Modules linked in:
> [ 7.118593] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.10.65 #196
> [ 7.118691] Hardware name: Generic DT based system
> [ 7.119088] Backtrace:
> [ 7.119675] [<8093aff0>] (dump_backtrace) from [<8093b294>]
> (show_stack+0x20/0x24)
> [ 7.120052] r7:00000009 r6:60000153 r5:00000000 r4:80e75938
> [ 7.120223] [<8093b274>] (show_stack) from [<80940938>]
> (dump_stack+0xc8/0xe4)
> [ 7.120298] [<80940870>] (dump_stack) from [<80123174>] (__warn+0xe8/0x154)
> [ 7.120355] r7:00000009 r6:00000be5 r5:804bc594 r4:80b53c80
> [ 7.120415] [<8012308c>] (__warn) from [<8093b9b4>]
> (warn_slowpath_fmt+0x6c/0xe4)
> [ 7.120465] r7:00000009 r6:00000be5 r5:80b53c80 r4:00000000
> [ 7.120537] [<8093b94c>] (warn_slowpath_fmt) from [<804bc594>]
> (blk_mq_release+0x84/0x114)
> [ 7.120594] r8:80b53c80 r7:857b7390 r6:00000001 r5:80ea6efd r4:00000000
> [ 7.120656] [<804bc510>] (blk_mq_release) from [<804ad65c>]
> (blk_release_queue+0xb8/0x128)
> [ 7.120756] r9:00000001 r8:80eee400 r7:00000000 r6:857b7390
> r5:00000001 r4:857b73d8
> [ 7.120836] [<804ad5a4>] (blk_release_queue) from [<8052f87c>]
> (kobject_put+0xc8/0x210)
> [ 7.120891] r7:00000000 r6:00000000 r5:80e751bc r4:857b73d8
> [ 7.120948] [<8052f7b4>] (kobject_put) from [<804a9b00>]
> (blk_put_queue+0x1c/0x20)
> [ 7.120998] r7:00000000 r6:857b3800 r5:00000000 r4:857b3860
> [ 7.121055] [<804a9ae4>] (blk_put_queue) from [<804c2784>]
> (disk_release+0xb0/0x118)
> [ 7.121118] [<804c26d4>] (disk_release) from [<805f717c>]
> (device_release+0x40/0xb4)
> [ 7.121168] r7:00000000 r6:00000000 r5:00000000 r4:857b3860
> [ 7.121224] [<805f713c>] (device_release) from [<8052f87c>]
> (kobject_put+0xc8/0x210)
> [ 7.121265] r5:80e81154 r4:857b3860
> [ 7.121318] [<8052f7b4>] (kobject_put) from [<804c1c74>] (put_disk+0x24/0x28)
> [ 7.121368] r7:ffffffea r6:00000008 r5:857b3800 r4:857bca00
> [ 7.121440] [<804c1c50>] (put_disk) from [<806286f4>]
> (nbd_dev_add+0x214/0x27c)
> [ 7.121670] [<806284e0>] (nbd_dev_add) from [<80d22f80>]
> (nbd_init+0xec/0x120)
> [ 7.121740] r10:80ec7000 r9:80c06b34 r8:80d39834 r7:00000000
> r6:80e82aa8 r5:00000009
> [ 7.121777] r4:00000000
> [ 7.121842] [<80d22e94>] (nbd_init) from [<80102364>]
> (do_one_initcall+0x50/0x274)
> [ 7.121893] r7:00000000 r6:00000007 r5:8116d180 r4:80d22e94
> [ 7.121956] [<80102314>] (do_one_initcall) from [<80d012e8>]
> (kernel_init_freeable+0x1b8/0x240)
> [ 7.122005] r7:80d39854 r6:00000007 r5:8116d180 r4:80d5e788
> [ 7.122067] [<80d01130>] (kernel_init_freeable) from [<80947bac>]
> (kernel_init+0x18/0x130)
> [ 7.122126] r10:00000000 r9:00000000 r8:00000000 r7:00000000
> r6:00000000 r5:80947b94
> [ 7.122161] r4:00000000
> [ 7.122218] [<80947b94>] (kernel_init) from [<80100168>]
> (ret_from_fork+0x14/0x2c)
> [ 7.122413] Exception stack(0x810b7fb0 to 0x810b7ff8)
> [ 7.122936] 7fa0: 00000000
> 00000000 00000000 00000000
> [ 7.123287] 7fc0: 00000000 00000000 00000000 00000000 00000000
> 00000000 00000000 00000000
> [ 7.123545] 7fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> [ 7.123728] r5:80947b94 r4:00000000
> [ 7.124011] ---[ end trace d69e5842dc8c9352 ]---
>
> There's been a bit going on in this driver since v5.10, so I assume
> it's missing some dependent changes.
>
Hi, Joel,
Thank you for report!
Did reverting my commit remove this warning? I don't get how sanity
check could cause this warning, but I might be missing something.
With regards,
Pavel Skripkin
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