lkml.org 
[lkml]   [2019]   [Feb]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [RFC v1 0/3] Address potential user-after-free on module unload
    On Wed, Feb 6, 2019 at 12:30 PM Dmitry Torokhov
    <dmitry.torokhov@gmail.com> wrote:
    >
    > Yeah. But devm irq gave most trouble because we did not have enough
    > devm APIs so we often ended up with mixed devm/non-devm usage and that
    > is what was causing most of the issues. If we can switch everything to
    > devm then devm irq is not that troublesome.
    >

    It sounds to me like _incomplete_ devm_ is worse than no devm at all.

    Imagine a devm_ resource depends on a non-devm one:

    int acme_probe(struct device *dev)
    {
    ...
    r = create_something();
    d = devm_create_thing(dev, r);
    }

    Then remove could get us into some serious trouble:

    void acme_remove(struct device *dev)
    {
    /* r _must_ be released here, we have no other place to do it */
    destroy_something(r);
    /* here, d is still alive because it's devm
    * which is cleaned up _after_ remove().
    * Now we have a live resource using a released resource.
    * use-after-free anyone?
    */
    }

    This is a more generalized version of the issue I originally
    observed, where r => struct work_struct.

    I'm sure there must be plenty of these around the codebase.

    I wish we had a Coccinelle script to catch these, because it's
    one thing to fix them today. More will be added tomorrow.
    devm_ is so elegant that people frequently use it without
    thinking it through.

    I certainly would have, before yesterday :)

    \
     
     \ /
      Last update: 2019-02-06 18:51    [W:2.547 / U:0.028 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site