Re: [syzbot] WARNING in internal_create_group
From: Pavel Skripkin
Date: Thu Sep 16 2021 - 06:56:21 EST
On 9/16/21 09:55, Joel Stanley wrote:
On Wed, 11 Aug 2021 at 21:39, Pavel Skripkin <paskripkin@xxxxxxxxx> 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