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Message-ID: <CALmYWFu_JFyuwYhDtEDWxEob8JHFSoyx_SCcsRVKqSYyyw30Rg@mail.gmail.com>
Date: Mon, 8 Jul 2024 09:08:29 -0700
From: Jeff Xu <jeffxu@...gle.com>
To: Florian Weimer <fweimer@...hat.com>
Cc: Mickaël Salaün <mic@...ikod.net>,
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Subject: Re: [RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2)
Hi
On Fri, Jul 5, 2024 at 11:03 AM Florian Weimer <fweimer@...hat.com> wrote:
>
> * Mickaël Salaün:
>
> > Add a new AT_CHECK flag to execveat(2) to check if a file would be
> > allowed for execution. The main use case is for script interpreters and
> > dynamic linkers to check execution permission according to the kernel's
> > security policy. Another use case is to add context to access logs e.g.,
> > which script (instead of interpreter) accessed a file. As any
> > executable code, scripts could also use this check [1].
>
> Some distributions no longer set executable bits on most shared objects,
> which I assume would interfere with AT_CHECK probing for shared objects.
> Removing the executable bit is attractive because of a combination of
> two bugs: a binutils wart which until recently always set the entry
> point address in the ELF header to zero, and the kernel not checking for
> a zero entry point (maybe in combination with an absent program
> interpreter) and failing the execve with ELIBEXEC, instead of doing the
> execve and then faulting at virtual address zero. Removing the
> executable bit is currently the only way to avoid these confusing
> crashes, so I understand the temptation.
>
Will dynamic linkers use the execveat(AT_CHECK) to check shared
libraries too ? or just the main executable itself.
Thanks.
-Jeff
> Thanks,
> Florian
>
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