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

[Rafael J. Wysocki]

On Thu, Oct 21, 2021 at 1:38 PM yebin <yebin10@xxxxxxxxxx> wrote:
>
>
>
> On 2021/10/21 19:00, Rafael J. Wysocki wrote:
> > On Wed, Oct 13, 2021 at 2:06 PM Ye Bin <yebin10@xxxxxxxxxx> 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?

> 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@xxxxxxxxxx>
> >> ---
> >>   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.

> >
> >>          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 {
> >> --
> > .
> >
>