[CRIU] [PATCH] UBUNTU: SAUCE: overlayfs: use shiftfs hacks only with shiftfs as underlay

[Adrian Reber]

Andrei, thanks for the fix. For CRIU this would be a really important
fix to have. Almost every week we have some CRIU user asking us why
checkpoint/restore no longer works in Travis with Docker and Ubuntu in
general and we always point our users to that bug and are telling users
to downgrade the kernel or switch to another graph driver for Docker.

If this fix would be applied that would help us really a lot.

		Adrian

On Sun, Apr 19, 2020 at 01:59:18AM -0700, Andrei Vagin wrote:
> 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: 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: Andrei Vagin <avagin at gmail.com>
> ---
>  fs/overlayfs/file.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 7b86d6080c22..c57cfe50f6cc 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -12,6 +12,7 @@
>  #include <linux/xattr.h>
>  #include <linux/uio.h>
>  #include <linux/uaccess.h>
> +#include <linux/magic.h>
>  #include "overlayfs.h"
>  
>  static char ovl_whatisit(struct inode *inode, struct inode *realinode)
> @@ -35,8 +36,12 @@ static struct file *ovl_open_realfile(const struct file *file,
>  
>  	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",
> -- 
> 2.17.1
> 
> _______________________________________________
> CRIU mailing list
> CRIU at openvz.org
> https://lists.openvz.org/mailman/listinfo/criu