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

On 2021/10/21 19:00, Rafael J. Wysocki wrote:

On Wed, Oct 13, 2021 at 2:06 PM Ye Bin [off-list ref] wrote:

quoted

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.
If the "/sys/power/resume" sysfs interface is unrestricted, it will provide
criminals with a way to attack the system.

quoted

Signed-off-by: Ye Bin <redacted>
---
  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.

quoted

         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 {
--

.