Re: [PATCH -next] PM: hibernate: Get block device exclusively when do swsusp_check

[yebin <yebin10@huawei.com>]

On 2021/10/21 21:27, Rafael J. Wysocki wrote:
> On Thu, Oct 21, 2021 at 1:38 PM yebin <yebin10@huawei.com> wrote:
>>
>>
>> On 2021/10/21 19:00, Rafael J. Wysocki wrote:
>>> On Wed, Oct 13, 2021 at 2:06 PM Ye Bin <yebin10@huawei.com> wrote:
>>>> We got follow issue:
>>>> [   89.266592] ------------[ cut here ]------------
>>>> [   89.267427] kernel BUG at fs/buffer.c:3020!
>>>> [   89.268264] invalid opcode: 0000 [#1] SMP KASAN PTI
>>>> [   89.269116] CPU: 7 PID: 1750 Comm: kmmpd-loop0 Not tainted 5.10.0-862.14.0.6.x86_64-08610-gc932cda3cef4-dirty #20
>>>> [   89.273169] RIP: 0010:submit_bh_wbc.isra.0+0x538/0x6d0
>>>> [   89.277157] RSP: 0018:ffff888105ddfd08 EFLAGS: 00010246
>>>> [   89.278093] RAX: 0000000000000005 RBX: ffff888124231498 RCX: ffffffffb2772612
>>>> [   89.279332] RDX: 1ffff11024846293 RSI: 0000000000000008 RDI: ffff888124231498
>>>> [   89.280591] RBP: ffff8881248cc000 R08: 0000000000000001 R09: ffffed1024846294
>>>> [   89.281851] R10: ffff88812423149f R11: ffffed1024846293 R12: 0000000000003800
>>>> [   89.283095] R13: 0000000000000001 R14: 0000000000000000 R15: ffff8881161f7000
>>>> [   89.284342] FS:  0000000000000000(0000) GS:ffff88839b5c0000(0000) knlGS:0000000000000000
>>>> [   89.285711] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> [   89.286701] CR2: 00007f166ebc01a0 CR3: 0000000435c0e000 CR4: 00000000000006e0
>>>> [   89.287919] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>> [   89.289138] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>>> [   89.290368] Call Trace:
>>>> [   89.290842]  write_mmp_block+0x2ca/0x510
>>>> [   89.292218]  kmmpd+0x433/0x9a0
>>>> [   89.294902]  kthread+0x2dd/0x3e0
>>>> [   89.296268]  ret_from_fork+0x22/0x30
>>>> [   89.296906] Modules linked in:
>>>>
>>>> We can reproduce this issue as follow:
>>>> 1. mkfs.ext4 -O mmp  /dev/sda -b 1024
>>>> 2. mount /dev/sda /home/test
>>>> 3. echo "/dev/sda" > /sys/power/resume
>>>> 4. wait a moment we will get exception
>>>>
>>>> The sequence of issue is as follows:
>>>>          Thread1                       Thread2
>>>> mount /dev/sda /home/test
>>>> get s_mmp_bh  --> has mapped flag
>>>> start kmmpd thread
>>>>                                   echo "/dev/sda" > /sys/power/resume
>>>>                                     resume_store
>>>>                                       software_resume
>>>>                                         swsusp_check
>>>>                                           set_blocksize
>>>>                                             truncate_inode_pages_range
>>>>                                               truncate_cleanup_page
>>>>                                                 block_invalidatepage
>>>>                                                   discard_buffer --> clean mapped flag
>>>> write_mmp_block
>>>>     submit_bh
>>>>       submit_bh_wbc
>>>>         BUG_ON(!buffer_mapped(bh)) --> trigger bug_on
>>>>
>>>> To solve this issue, get block device exclusively when do swsusp_check.
>>> And why exactly is this going to help?
>> If a  block device is already  mounted, then do  resume, it will discard
>> buffer
>> which file system being used.  That can cause the file system to crash and
>> may even cause the system to reset abnormally.
> I see.
>
> Is there a way to indicate in swsusp_check() that the access will be
> read-only and so it doesn't care whether or not the block device is in
> use by someone else?
The root reason is that call  'set_blocksize' in 'swsusp_check' which 
maybe invalidate
block device's page.
Moreover, the file system and swap partition share storage space, which 
will lead to
data confusion.
>> If the "/sys/power/resume" sysfs interface is unrestricted, it will provide
>> criminals with a way to attack the system.
>>
>>>> Signed-off-by: Ye Bin <yebin10@huawei.com>
>>>> ---
>>>>    kernel/power/swap.c | 5 +++--
>>>>    1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
>>>> index 9ec418955556..26c0bd2a50da 100644
>>>> --- a/kernel/power/swap.c
>>>> +++ b/kernel/power/swap.c
>>>> @@ -1521,9 +1521,10 @@ int swsusp_read(unsigned int *flags_p)
>>>>    int swsusp_check(void)
>>>>    {
>>>>           int error;
>>>> +       void *holder;
>>>>
>>>>           hib_resume_bdev = blkdev_get_by_dev(swsusp_resume_device,
>>>> -                                           FMODE_READ, NULL);
>>>> +                                           FMODE_READ | FMODE_EXCL, &holder);
>>> So you need to explain to me how this works.
>> As we call 'blkdev_get_by_path' in 'mount_bdev'  pass mode includes
>> FMODE_EXCL.
>> So if 'swsusp_check' try to get block device with mode includes
>> FMODE_EXCL will failed.
>>
>> I think if a block device is used as a swap partition, it cannot be
>> mounted at the
>> same time. Conversely, if a block device is already mounted, it cannot
>> be used as
>> a swap partition.
> Well, what if a hibernation image is located in a swap file?  This is
> one of the cases that need to be supported.
I don't know much about this, but I think the process can call 
swsusp_check, the
hibernation image must be loaded into the block device.

I refer to the process of swapon. If the swap partition is a block 
device, it is also
opened exclusively.
swapon
     claim_swapfile
static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
{
         int error;

         if (S_ISBLK(inode->i_mode)) {    -->If a block device is 
specified, it is also opened exclusively here.
                 p->bdev = blkdev_get_by_dev(inode->i_rdev,
                                    FMODE_READ | FMODE_WRITE | 
FMODE_EXCL, p);
                 if (IS_ERR(p->bdev)) {
                         error = PTR_ERR(p->bdev);
                         p->bdev = NULL;
                         return error;
                 }
                 p->old_block_size = block_size(p->bdev);
                 error = set_blocksize(p->bdev, PAGE_SIZE);
                 if (error < 0)
                         return error;
                 /*
                  * Zoned block devices contain zones that have a sequential
                  * write only restriction.  Hence zoned block devices 
are not
                  * suitable for swapping.  Disallow them here.
                  */
                 if (blk_queue_is_zoned(p->bdev->bd_disk->queue))
                         return -EINVAL;
                 p->flags |= SWP_BLKDEV;
         } else if (S_ISREG(inode->i_mode)) {
                 p->bdev = inode->i_sb->s_bdev;
         }

         return 0;
}
>>>>           if (!IS_ERR(hib_resume_bdev)) {
>>>>                   set_blocksize(hib_resume_bdev, PAGE_SIZE);
>>>>                   clear_page(swsusp_header);
>>>> @@ -1545,7 +1546,7 @@ int swsusp_check(void)
>>>>
>>>>    put:
>>>>                   if (error)
>>>> -                       blkdev_put(hib_resume_bdev, FMODE_READ);
>>>> +                       blkdev_put(hib_resume_bdev, FMODE_READ | FMODE_EXCL);
>>>>                   else
>>>>                           pr_debug("Image signature found, resuming\n");
>>>>           } else {
>>>> --
>>> .
>>>
> .
>