Re: [PATCH] fix namespaced fscaps when !CONFIG_SECURITY

Serge E. Hallyn
2020-11-29T21:16:31Z

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 )

thanks,
-serge

On Tue, Nov 17, 2020 at 08:09:59AM -0800, Andrew G. Morgan wrote:
> Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
>
>
> On Tue, Nov 17, 2020 at 7:09 AM Serge E. Hallyn <serge@hallyn.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@hallyn.com>
> > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1593431
> > Cc: Hervé Guillemet <herve@guillemet.org>
> > Cc: Andrew G. Morgan <morgan@kernel.org>
> > Cc: Casey Schaufler <casey@schaufler-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
> >
> >