[jira] [Commented] (MESOS-3335) FlagsBase copy-ctor leads to dangling pointer.

["Michael Park (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MESOS-3335?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15438155#comment-15438155 ] 

Michael Park commented on MESOS-3335:
-------------------------------------

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commit f3181999fd03c99078994855687749839eb5365f
Author: Benjamin Bannier <be...@mesosphere.io>
Date:   Thu Aug 25 13:53:15 2016 -0700

    Avoided slicing of flags from `subprocess` in mesos.

    While `FlagsBase` internally stores just maps of names and
    flags, the functions stored in a `Flag` rely on the original type of
    the `Flags` containing them (e.g., we perform dynamic casts to detect
    their types).

    Since `Option<T>` stores `T` as a value (i.e., it cannot contain
    reference types) any interface taking an `Option<T>` cannot rely on
    polymorphic behavior of `T`. To make use of polymorphism we should
    instead store e.g., a pointer type to avoid slicing.

    Here we change `Flags` arguments of `subprocess` to allow preserving
    the original type so `Flag` functions can work reliably; we do this by
    passing a non-owning pointer to a `Flags` so we do not restrict copying.

    Review: https://reviews.apache.org/r/46822/
{noformat}
{noformat}
commit d05625fd7dc8cdf8c0007f2d9ddd2d739cfd9f5d
Author: Benjamin Bannier <be...@mesosphere.io>
Date:   Thu Aug 25 13:53:10 2016 -0700

    Avoided slicing of flags from `subprocess` in libprocess.

    While `FlagsBase` internally stores just maps of names and
    flags, the functions stored in a `Flag` rely on the original type of
    the `Flags` containing them (e.g., we perform dynamic casts to detect
    their types).

    Since `Option<T>` stores `T` as a value (i.e., it cannot contain
    reference types) any interface taking an `Option<T>` cannot rely on
    polymorphic behavior of `T`. To make use of polymorphism we should
    instead store e.g., a pointer type to avoid slicing.

    Here we change `Flags` arguments of `subprocess` to allow preserving
    the original type so `Flag` functions can work reliably; we do this by
    passing a non-owning pointer to a `Flags` so we do not restrict copying.

    Review: https://reviews.apache.org/r/46821/
{noformat}

> FlagsBase copy-ctor leads to dangling pointer.
> ----------------------------------------------
>
>                 Key: MESOS-3335
>                 URL: https://issues.apache.org/jira/browse/MESOS-3335
>             Project: Mesos
>          Issue Type: Bug
>            Reporter: Neil Conway
>            Assignee: Benjamin Bannier
>              Labels: mesosphere
>         Attachments: lambda_capture_bug.cpp
>
>
> Per [#3328], ubsan detects the following problem:
> [ RUN ] FaultToleranceTest.ReregisterCompletedFrameworks
> /mesos/3rdparty/libprocess/3rdparty/stout/include/stout/flags/flags.hpp:303:25: runtime error: load of value 33, which is not a valid value for type 'bool'
> I believe what is going on here is the following:
> * The test calls StartMaster(), which does MesosTest::CreateMasterFlags()
> * MesosTest::CreateMasterFlags() allocates a new master::Flags on the stack, which is subsequently copy-constructed back to StartMaster()
> * The FlagsBase constructor is:
> bq. {{FlagsBase() { add(&help, "help", "...", false); }}}
> where "help" is a member variable -- i.e., it is allocated on the stack in this case.
> * {{FlagsBase()::add}} captures {{&help}}, e.g.:
> {noformat}
> flag.stringify = [t1](const FlagsBase&) -> Option<std::string> {
>     return stringify(*t1);
>   };}}
> {noformat}
> * The implicit copy constructor for FlagsBase is just going to copy the lambda above, i.e., the result of the copy constructor will have a lambda that points into MesosTest::CreateMasterFlags()'s stack frame, which is bad news.
> Not sure the right fix -- comments welcome. You could define a copy-ctor for FlagsBase that does something gross (basically remove the old help flag and define a new one that points into the target of the copy), but that seems, well, gross.
> Probably not a pressing-problem to fix -- AFAICS worst symptom is that we end up reading one byte from some random stack location when serving {{state.json}}, for example.



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