ACK[U/F]/cmnt: [SRU][UNSTABLE][PATCH] UBUNTU: SAUCE: shiftfs: record correct creator credentials

[Christian Brauner]

On Thu, Apr 23, 2020 at 03:12:01PM +0200, Kleber Souza wrote:
> On 10.04.20 16:55, Christian Brauner wrote:
> > From: Christian Brauner <christian.brauner at ubuntu.com>
> > 
> > BugLink: https://bugs.launchpad.net/bugs/1872094
> > 
> > When shiftfs is nested we failed to be able to create any files or
> > access directories because we recorded the wrong creator credentials. We
> > need to record the credentials of the creator of the lowers mark mount
> > of shiftfs. Otherwise we aren't privileged wrt to the shiftfs layer in
> > the nesting case. This is similar to how we always record the user
> > namespace of the base filesystem.
> > 
> > Suggested-by: Seth Forshee <seth.forshee at canonical.com>
> > Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
> 
> For Focal as well:
> 
> Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
> 
> 
> Should this be applied to Eoan? Eoan has shiftfs but it's not an LTS.

Yes, sorry. This should basically go to any versions that we still
support with shiftfs.

Thank!
Christian

> 
> Thanks,
> Kleber
> 
> > ---
> >  fs/shiftfs.c | 17 +++++++++--------
> >  1 file changed, 9 insertions(+), 8 deletions(-)
> > 
> > diff --git a/fs/shiftfs.c b/fs/shiftfs.c
> > index 3623d02b061e..5c39529d0a17 100644
> > --- a/fs/shiftfs.c
> > +++ b/fs/shiftfs.c
> > @@ -2020,6 +2020,7 @@ static int shiftfs_fill_super(struct super_block *sb, void *raw_data,
> >  			 * parent mark mountpoint.
> >  			 */
> >  			sbinfo->passthrough_mark = sbinfo_mp->passthrough_mark;
> > +			sbinfo->creator_cred = get_cred(sbinfo_mp->creator_cred);
> >  		} else {
> >  			sbinfo->mnt = mntget(path.mnt);
> >  			dentry = dget(path.dentry);
> > @@ -2028,16 +2029,16 @@ static int shiftfs_fill_super(struct super_block *sb, void *raw_data,
> >  			 * are identical.
> >  			 */
> >  			sbinfo->passthrough_mark = sbinfo->passthrough;
> > -		}
> >  
> > -		cred_tmp = prepare_creds();
> > -		if (!cred_tmp) {
> > -			err = -ENOMEM;
> > -			goto out_put_path;
> > +			cred_tmp = prepare_creds();
> > +			if (!cred_tmp) {
> > +				err = -ENOMEM;
> > +				goto out_put_path;
> > +			}
> > +			/* Don't override disk quota limits or use reserved space. */
> > +			cap_lower(cred_tmp->cap_effective, CAP_SYS_RESOURCE);
> > +			sbinfo->creator_cred = cred_tmp;
> >  		}
> > -		/* Don't override disk quota limits or use reserved space. */
> > -		cap_lower(cred_tmp->cap_effective, CAP_SYS_RESOURCE);
> > -		sbinfo->creator_cred = cred_tmp;
> >  	} else {
> >  		/*
> >  		 * This leg executes if we're admin capable in the namespace,
> > 
> > base-commit: eb813ecd261d2c4c592bd4116aaa93f33c9ec4bd
> > 
>