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    SubjectRe: [PATCH] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs
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    On Thu, Jan 12, 2012 at 10:02 PM, Andy Lutomirski <luto@amacapital.net> wrote:
    > On Thu, Jan 12, 2012 at 9:58 PM, Kees Cook <keescook@chromium.org> wrote:
    >> On Thu, Jan 12, 2012 at 6:12 PM, Andy Lutomirski <luto@amacapital.net> wrote:
    >>> With this set, a lot of dangerous operations (chroot, unshare, etc)
    >>> become a lot less dangerous because there is no possibility of
    >>> subverting privileged binaries.
    >>>
    >>> This patch completely breaks apparmor.  Someone who understands (and
    >>> uses) apparmor should fix it or at least give me a hint.
    >>>
    >>> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
    >>> [....]
    >>> diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
    >>> index c1e18ba..7f480b7 100644
    >>> --- a/security/apparmor/domain.c
    >>> +++ b/security/apparmor/domain.c
    >>> @@ -360,6 +360,9 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
    >>>        if (bprm->cred_prepared)
    >>>                return 0;
    >>>
    >>> +       /* XXX: someone who understands apparmor needs to fix this. */
    >>> +       BUG_ON(bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS);
    >>> +
    >>>        cxt = bprm->cred->security;
    >>>        BUG_ON(!cxt);
    >>>
    >>
    >> Since apparmor_bprm_set_creds() calls cap_bprm_set_creds() already[1],
    >> I think AppArmor needs no changes at all, but John will know better.
    >> :)
    >
    > I think that AppArmor determines what a program is allowed to do by
    > looking at the path of the executable.  We don't want newly-executed
    > programs to gain permissions because they're a different executable
    > when we're in no_new_privs mode, so (if I'm right) something different
    > needs to happen.

    I'll have to go look more closely. I thought cap_bprm_set_creds() was
    already evaluating the new privs and blocking any gained privs with
    the changes you were making.

    -Kees

    --
    Kees Cook
    ChromeOS Security
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