NAK/Cmnt: [PATCH] UBUNTU: SAUCE: overlayfs: fix incorrect mnt_id of files opened from map_files

[Alexander Mihalicyn]

Hi,

thank you for your comments. I've resent the patch
https://lists.ubuntu.com/archives/kernel-team/2021-April/119546.html

>Why is this inline? I see it is being used only in one place, so it
Sure, I will fix that.

Regards,
Alex

On Mon, Apr 26, 2021 at 10:38 AM Krzysztof Kozlowski
<krzysztof.kozlowski at canonical.com> wrote:
>
> On 26/04/2021 09:01, alexander at mihalicyn.com wrote:
> > From: Alexander Mikhalitsyn <alexander at mihalicyn.com>
> >
> > 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
>
> Thanks for the patch.
>
> It seems you are posting it for Focal, so you need to follow the SRU
> process:
> https://wiki.ubuntu.com/Kernel/Dev/StablePatchFormat
>
> >
> > 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: Christian Brauner <christian.brauner at ubuntu.com>
> > Cc: Stefan Bader <stefan.bader at canonical.com>
> > Cc: Connor Kuehl <connor.kuehl at canonical.com>
> > Cc: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
> >
> > Fixes: 58009298c6bd ("UBUNTU: SAUCE: overlayfs: allow with shiftfs as underlay")
> > Signed-off-by: Alexander Mikhalitsyn <alexander at mihalicyn.com>
> > ---
> >  fs/overlayfs/file.c      | 17 +++++++++++++++++
> >  fs/overlayfs/overlayfs.h | 12 ++++++++++++
> >  2 files changed, 29 insertions(+)
> >
> > diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> > index 0d3ea0cf3e98..7e63eb52bb0d 100644
> > --- a/fs/overlayfs/file.c
> > +++ b/fs/overlayfs/file.c
> > @@ -351,6 +351,23 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
> >               vma->vm_file = file;
> >               fput(realfile);
> >       } else {
> > +             /*
> > +              * In map_files_get_link() (fs/proc/base.c)
> > +              * we need to determine correct path from overlayfs.
> > +              * But real_mount(realfile->f_path.mnt) may be not
> > +              * equal to real_mount(file->f_path.mnt). In such case
> > +              * fdinfo of the same file which was opened from
> > +              * /proc/<pid>/map_files/... and "usual" path
> > +              * will show different mnt_id.
> > +              *
> > +              * We solve issue like in aufs by using additional
> > +              * field on struct vm_area_struct called "vm_prfile"
> > +              * which is used only for fdinfo/"printing" needs.
> > +              *
> > +              * See also mm/prfile.c
> > +              */
> > +             ovl_vm_prfile_set(vma, file);
> > +
> >               /* Drop reference count from previous vm_file value */
> >               fput(file);
> >       }
> > diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> > index 5f0188807666..a4e6023b4fdb 100644
> > --- a/fs/overlayfs/overlayfs.h
> > +++ b/fs/overlayfs/overlayfs.h
> > @@ -442,3 +442,15 @@ int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
> >
> >  /* export.c */
> >  extern const struct export_operations ovl_export_operations;
> > +
> > +/* handle vma->vm_prfile */
> > +static inline void ovl_vm_prfile_set(struct vm_area_struct *vma,
> > +                                 struct file *file)
>
> Why is this inline? I see it is being used only in one place, so it
> should be regular static inside file.c. It seems you copied the pattern
> from aufs but I have doubts that it's better to keep it the same way.
>
> > +{
> > +     get_file(file);
> > +     vma->vm_prfile = file;
> > +#ifndef CONFIG_MMU
> > +     get_file(file);
> > +     vma->vm_region->vm_prfile = file;
> > +#endif
> > +}
> >
>
>
> Best regards,
> Krzysztof