[CRIU] [SRU][F][G][H][PATCH v2] UBUNTU: SAUCE: overlayfs: fix incorrect mnt_id of files opened from map_files

[Krzysztof Kozlowski]

On 27/04/2021 11:46, Christian Brauner wrote:
> On Mon, Apr 26, 2021 at 11:11:21AM +0300, alexander at mihalicyn.com wrote:
>> From: Alexander Mikhalitsyn <alexander at mihalicyn.com>
>>
>> BugLink: https://bugs.launchpad.net/bugs/1857257
>>
>> The hack was introduced in ("UBUNTU: SAUCE: overlayfs: allow with
>> shiftfs as underlay") and it broke checkpoint/restore of docker
>> contains:
>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1857257
>>
>> The following script can be used to trigger the issue:
>>   #!/bin/bash
>>
>>   cat > test.py << EOF
>>   import sys
>>
>>   f = open("/proc/self/maps")
>>
>>   for l in f.readlines():
>>     if "python" not in l:
>>       continue
>>     print(l)
>>     s = l.split()
>>     start, end = s[0].split("-")
>>     fname = s[-1]
>>     print(start, end, fname)
>>     break
>>   else:
>>     sys.exit(1)
>>
>>   test_file1 = open(fname)
>>   test_file2 = open("/proc/self/map_files/%s-%s" % (start, end))
>>
>>   fdinfo1 = open("/proc/self/fdinfo/%d" % test_file1.fileno()).read()
>>   fdinfo2 = open("/proc/self/fdinfo/%d" % test_file2.fileno()).read()
>>
>>   if fdinfo1 != fdinfo2:
>>     print("FAIL")
>>     print(test_file1)
>>     print(fdinfo1)
>>     print(test_file2)
>>     print(fdinfo2)
>>     sys.exit(1)
>>   print("PASS")
>>   EOF
>>   sudo docker run -it --privileged --rm -v `pwd`:/mnt python python /mnt/test.py
>>
>> Thanks to Andrei Vagin for the reproducer and investigation of this problem.
>>
>> Cc: Andrei Vagin <avagin at gmail.com>
>> Cc: Adrian Reber <areber at redhat.com>
>> Cc: Christian Brauner <christian.brauner at ubuntu.com>
>> Cc: Stefan Bader <stefan.bader at canonical.com>
>> Cc: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
>> Cc: Krzysztof Kozlowski <krzysztof.kozlowski at canonical.com>
>>
>> Fixes: d24b8a5 ("UBUNTU: SAUCE: overlayfs: allow with shiftfs as underlay")
>> Signed-off-by: Alexander Mikhalitsyn <alexander at mihalicyn.com>
>> ---
> 
> Hey,
> 
> Thanks for the patch!
> Fwiw, Andrei already tried to fix this a while ago but it caused another
> regression which forced us to revert the fix for this issue.

Did you mean you tried this patch and it caused regressions?

> 
>>  fs/overlayfs/file.c | 29 +++++++++++++++++++++++++++++
>>  1 file changed, 29 insertions(+)
>>
>> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
>> index 0d3ea0cf3e98..5fa520d0798e 100644
>> --- a/fs/overlayfs/file.c
>> +++ b/fs/overlayfs/file.c
>> @@ -325,6 +325,18 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
>>  	return ret;
>>  }
>>  
>> +/* handle vma->vm_prfile */
>> +static void ovl_vm_prfile_set(struct vm_area_struct *vma,
>> +			      struct file *file)
>> +{
>> +	get_file(file);
>> +	vma->vm_prfile = file;
>> +#ifndef CONFIG_MMU
>> +	get_file(file);
>> +	vma->vm_region->vm_prfile = file;
>> +#endif
>> +}
> 
> I'm confused struct vm_area_struct doesn't have a vm_prfile entry. Can
> you explain, please?

It has. The aufs patchset brought it and basically this patch depends on
aufs.

Best regards,
Krzysztof