ACK: [SRU][UNSTABLE/BIONIC/XENIAL][PATCH] UBUNTU: SAUCE: overlayfs: use shiftfs hacks only with shiftfs as underlay

[Kamal Mostafa]

Acked-by: Kamal Mostafa <kamal at canonical.com>

 -Kamal

On Thu, Apr 23, 2020 at 12:11:28PM +0200, Christian Brauner wrote:
> From: Andrei Vagin <avagin at gmail.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
> 
> 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")
> Acked-by: Christian Brauner <christian.brauner at ubuntu.com>
> Signed-off-by: Andrei Vagin <avagin at gmail.com>
> ---
>  fs/overlayfs/file.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 4f94ef663569..9d16fff5342a 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -42,9 +42,12 @@ static struct file *ovl_open_realfile(const struct file *file,
>  	int flags = file->f_flags | O_NOATIME | FMODE_NONOTIFY;
>  
>  	old_cred = ovl_override_creds(inode->i_sb);
> -	ovl_path_real(file->f_path.dentry, &realpath);
> -	realfile = open_with_fake_path(&realpath, flags, realinode,
> -				       current_cred());
> +	if (realpath.dentry->d_sb->s_magic == SHIFTFS_MAGIC)
> +		realfile = open_with_fake_path(&realpath, flags, realinode,
> +					       current_cred());
> +	else
> +		realfile = open_with_fake_path(&file->f_path, flags, realinode,
> +					       current_cred());
>  	revert_creds(old_cred);
>  
>  	pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
> 
> base-commit: 48f168950cd193d9beedc0afb0c79a254e32f637
> -- 
> 2.26.2
> 
> 
> -- 
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