Re: sys_setpriority error

From: Chris Wright (chrisat_private)
Date: Thu May 31 2001 - 00:17:18 PDT

  • Next message: George Ross: "Re: 2001-05-27 patch against 2.4.5"

    * David Wagner (dawat_private) wrote:
    > Chris Wright  wrote:
    > >The current implementation allows the module to override other factors in
    > >giving you permission.  It does _not_ allow the module to override other
    > >factors in denying permission.
    > That's backwards from what we need for security!
    > The kernel is permissive enough already.  What we most desperately
    > need is to make it more strict.
    > This seems really fundamental.  Am I missing something?
    To be clear, I am speaking of a very specific line of code in the
    sys_setpriority function.  This code said:
    if (p->uid != current->euid &&
        p->uid != current->uid && !capable(CAP_SYS_NICE)) {
    Now it looks like:
    no_nice = security_ops->task_ops->setnice(p, niceval);
    if (p->uid != current->euid &&
        p->uid != current->uid && no_nice) {
    I am not saying that in general lsm hooks are intended to only to grant
    permission and never authoritatively deny permission.
    Many lsm hooks have authoritative control.  The problem areas are the
    replacements to capable() calls in ugly compound conditionals.
    > P.S. I'm surprised that you call the current approach conservative.
    > It seems the most conservative approach is to say "A LSM is only
    > allowed to further restrict what an application can do"; this is
    > conservative because it means that if an attack is allowed with the
    > LSM, then it would have been allowed without the LSM, too.  In other
    > words, my suggested approach is fail-safe, whereas the current approach
    > is fail-open.
    Sorry to mislead.  What I meant by conservative is not change any core logic
    in the kernel.  The standard (non-lsm) kernel uses capabilities to override
    allow as defined by posix, so this behavior persists in the lsm kernel to
    preserve capabilities.
    linux-security-module mailing list

    This archive was generated by hypermail 2b30 : Thu May 31 2001 - 00:20:34 PDT