Messages in this thread | | | Date | Wed, 1 Feb 2012 11:02:23 -0800 | Subject | Re: [PATCH v3 3/4] Allow unprivileged CLONE_NEWUTS and CLONE_NEWIPC with no_new_privs | From | Kees Cook <> |
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On Mon, Jan 30, 2012 at 8:17 AM, Andy Lutomirski <luto@amacapital.net> wrote: > They are normally disallowed because they could be used to subvert > setuid programs. But if setuid is disabled, then they are safe. > > Signed-off-by: Andy Lutomirski <luto@amacapital.net> > --- > kernel/nsproxy.c | 8 +++++++- > 1 files changed, 7 insertions(+), 1 deletions(-) > > diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c > index b576f7f..47cf873 100644 > --- a/kernel/nsproxy.c > +++ b/kernel/nsproxy.c > @@ -191,7 +191,13 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags, > CLONE_NEWNET))) > return 0; > > - if (!capable(CAP_SYS_ADMIN)) > + /* We require either no_new_privs or CAP_SYS_ADMIN for all modes */ > + if (!current->no_new_privs && !capable(CAP_SYS_ADMIN)) > + return -EPERM; > + > + /* NEWNS and NEWNET always require CAP_SYS_ADMIN. */ > + if ((unshare_flags & (CLONE_NEWNS | CLONE_NEWNET)) && > + !capable(CAP_SYS_ADMIN)) > return -EPERM; > > *new_nsp = create_new_namespaces(unshare_flags, current,
While I think it's unlikely that the list handled by unshare_nsproxy_namespaces() is going to change, I'd still prefer that the logic of this test be reversed so that the nnp-allowed flags are listed instead of the CAP_SYS_ADMIN-required ones so that it will default to disallowing new flags. It's a little less readable, but maybe something like this (untested):
unsigned long handled_mask = (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWNET); unsigned long npp_mask = (CLONE_NEWUTS | CLONE_NEWIPC);
if (!(unshare_flags & handled_mask)) return 0;
if ( !(current->no_new_privs && !(unshare_flags & (handled_mask ^ npp_mask))) && !capable(CAP_SYS_ADMIN)) return -EPERM; ...
This also has the side-effect of removing the double-check of capable() in some cases.
-Kees
-- Kees Cook ChromeOS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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