linux-kernel - Re: [PATCH 1/2] ecryptfs: fix uid translation for setxattr on security.capability

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Date:   Mon, 25 Jan 2021 14:46:01 +0100
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     Tyler Hicks <code@...icks.com>
Cc:     "Eric W . Biederman" <ebiederm@...ssion.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-security-module@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>,
        "Serge E . Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH 1/2] ecryptfs: fix uid translation for setxattr on security.capability

On Mon, Jan 25, 2021 at 2:25 PM Miklos Szeredi <mszeredi@...hat.com> wrote:
>
> On Fri, Jan 22, 2021 at 7:31 PM Tyler Hicks <code@...icks.com> wrote:
> >
> > On 2021-01-19 17:22:03, Miklos Szeredi wrote:
> > > Prior to commit 7c03e2cda4a5 ("vfs: move cap_convert_nscap() call into
> > > vfs_setxattr()") the translation of nscap->rootid did not take stacked
> > > filesystems (overlayfs and ecryptfs) into account.
> > >
> > > That patch fixed the overlay case, but made the ecryptfs case worse.
> >
> > Thanks for sending a fix!
> >
> > I know that you don't have an eCryptfs setup to test with but I'm at a
> > loss about how to test this from the userns/fscaps side of things. Do
> > you have a sequence of unshare/setcap/getcap commands that I can run on
> > a file inside of an eCryptfs mount to verify that the bug exists after
> > 7c03e2cda4a5 and then again to verify that this patch fixes the bug?
>
> You need two terminals:
> $ = <USER>
> # = root
>
> $ unshare -Um
> $ echo $$
> <PID>
> # echo "0 1000 1" > uid_map

NOTE:  <USER> is assumed to have uid=1000, so this and following
"1000" values need to be fixed up if it's not the case.

Thanks,
Miklos