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    Subject[PATCH 3.17 49/73] userns: Dont allow unprivileged creation of gid mappings
    Date
    3.17-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: "Eric W. Biederman" <ebiederm@xmission.com>

    commit be7c6dba2332cef0677fbabb606e279ae76652c3 upstream.

    As any gid mapping will allow and must allow for backwards
    compatibility dropping groups don't allow any gid mappings to be
    established without CAP_SETGID in the parent user namespace.

    For a small class of applications this change breaks userspace
    and removes useful functionality. This small class of applications
    includes tools/testing/selftests/mount/unprivilged-remount-test.c

    Most of the removed functionality will be added back with the addition
    of a one way knob to disable setgroups. Once setgroups is disabled
    setting the gid_map becomes as safe as setting the uid_map.

    For more common applications that set the uid_map and the gid_map
    with privilege this change will have no affect.

    This is part of a fix for CVE-2014-8989.

    Reviewed-by: Andy Lutomirski <luto@amacapital.net>
    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/user_namespace.c | 4 ----
    1 file changed, 4 deletions(-)

    --- a/kernel/user_namespace.c
    +++ b/kernel/user_namespace.c
    @@ -821,10 +821,6 @@ static bool new_idmap_permitted(const st
    kuid_t uid = make_kuid(ns->parent, id);
    if (uid_eq(uid, file->f_cred->fsuid))
    return true;
    - } else if (cap_setid == CAP_SETGID) {
    - kgid_t gid = make_kgid(ns->parent, id);
    - if (gid_eq(gid, file->f_cred->fsgid))
    - return true;
    }
    }




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