linux-kernel - Re: [PATCH] fix namespaced fscaps when !CONFIG

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Message-ID: <alpine.LRH.2.21.2012011358200.28022@namei.org>
Date:   Tue, 1 Dec 2020 13:58:25 +1100 (AEDT)
From:   James Morris <jmorris@...ei.org>
To:     "Serge E. Hallyn" <serge@...lyn.com>
cc:     "Andrew G. Morgan" <morgan@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Hervé Guillemet <herve@...llemet.org>,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] fix namespaced fscaps when !CONFIG_SECURITY

On Sun, 29 Nov 2020, Serge E. Hallyn wrote:

> Hi James,
> 
> would you mind adding this to the security tree?  (You can cherrypick
> from https://git.kernel.org/pub/scm/linux/kernel/git/sergeh/linux.git/commit/?h=2020-11-29/fix-nscaps )

Sure.

> 
> thanks,
> -serge
> 
> On Tue, Nov 17, 2020 at 08:09:59AM -0800, Andrew G. Morgan wrote:
> > Signed-off-by: Andrew G. Morgan <morgan@...nel.org>
> > 
> > 
> > On Tue, Nov 17, 2020 at 7:09 AM Serge E. Hallyn <serge@...lyn.com> wrote:
> > 
> > > Namespaced file capabilities were introduced in 8db6c34f1dbc .
> > > When userspace reads an xattr for a namespaced capability, a
> > > virtualized representation of it is returned if the caller is
> > > in a user namespace owned by the capability's owning rootid.
> > > The function which performs this virtualization was not hooked
> > > up if CONFIG_SECURITY=n.  Therefore in that case the original
> > > xattr was shown instead of the virtualized one.
> > >
> > > To test this using libcap-bin (*1),
> > >
> > > $ v=$(mktemp)
> > > $ unshare -Ur setcap cap_sys_admin-eip $v
> > > $ unshare -Ur setcap -v cap_sys_admin-eip $v
> > > /tmp/tmp.lSiIFRvt8Y: OK
> > >
> > > "setcap -v" verifies the values instead of setting them, and
> > > will check whether the rootid value is set.  Therefore, with
> > > this bug un-fixed, and with CONFIG_SECURITY=n, setcap -v will
> > > fail:
> > >
> > > $ v=$(mktemp)
> > > $ unshare -Ur setcap cap_sys_admin=eip $v
> > > $ unshare -Ur setcap -v cap_sys_admin=eip $v
> > > nsowner[got=1000, want=0],/tmp/tmp.HHDiOOl9fY differs in []
> > >
> > > Fix this bug by calling cap_inode_getsecurity() in
> > > security_inode_getsecurity() instead of returning
> > > -EOPNOTSUPP, when CONFIG_SECURITY=n.
> > >
> > > *1 - note, if libcap is too old for getcap to have the '-n'
> > > option, then use verify-caps instead.
> > >
> > > Signed-off-by: Serge Hallyn <serge@...lyn.com>
> > > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1593431
> > > Cc: Hervé Guillemet <herve@...llemet.org>
> > > Cc: Andrew G. Morgan <morgan@...nel.org>
> > > Cc: Casey Schaufler <casey@...aufler-ca.com>
> > > ---
> > >  include/linux/security.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/security.h b/include/linux/security.h
> > > index bc2725491560..39642626a707 100644
> > > --- a/include/linux/security.h
> > > +++ b/include/linux/security.h
> > > @@ -869,7 +869,7 @@ static inline int security_inode_killpriv(struct
> > > dentry *dentry)
> > >
> > >  static inline int security_inode_getsecurity(struct inode *inode, const
> > > char *name, void **buffer, bool alloc)
> > >  {
> > > -       return -EOPNOTSUPP;
> > > +       return cap_inode_getsecurity(inode, name, buffer, alloc);
> > >  }
> > >
> > >  static inline int security_inode_setsecurity(struct inode *inode, const
> > > char *name, const void *value, size_t size, int flags)
> > > --
> > > 2.25.1
> > >
> > >
> 

-- 
James Morris
<jmorris@...ei.org>