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[PATCH 0/4] make call_usermodehelper a bit more "safe"

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Hi all,

Here's a second cut at my attempt to make call_usermodehelper a bit more
"safe".  It includes some patches from my previous series, and one new
one.  In all, this is a much smaller patchset, with better functionality
in the end.

The issue is that if you end up getting write access to kernel memory,
if you change the string '/sbin/hotplug' to point to
'/home/hacked/my_binary', then the next uevent that the system makes
will call this binary instead of the "trusted" one.

This series addresses this issue by doing two different things.  The
first 2 patches move a lot of existing call_usermodehelper binaries to
read-only memory, preventing them from being able to be changed at all.

The last patch introduces a new configuration option,
STATIC_USERMODEHELPER.  This option routes all call_usermodehelper()
calls to a single userspace binary.  That binary can then
filter/mediate/blacklist/whitelist/whatever the "real" usermodehelper
binaries and call them as needed (it determines the real one by looking
at the first argument.)

The location of this new binary can be set with the
STATIC_USERMODEHELPER_PATH configuration option.

If the user wants call_usermodehelper() to be disabled entirely,
STATIC_USERMODEHELPER_PATH can be set to "", which will cause all
call_usermodehelper() calls to do nothing, but return successful.

Many thanks to the reviewers of the last patch series for their hints on
how to mark strings properly to live in read-only memory always, and to
Neil Brown for the idea of STATIC_USERMODEHELPER.

If there are no complaints about these patches, I'll take them through
my driver-core tree.

thanks,

greg k-h

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[PATCH 0/4] make call_usermodehelper a bit more "safe" Greg KH <gregkh@linuxfoundation.org> - 2017-01-16 17:50 +0100
  [PATCH 2/3] Make static usermode helper binaries constant Greg KH <gregkh@linuxfoundation.org> - 2017-01-16 18:00 +0100
    Re: [PATCH 2/3] Make static usermode helper binaries constant "J. Bruce Fields" <bfields@fieldses.org> - 2017-01-16 22:30 +0100
      Re: [PATCH 2/3] Make static usermode helper binaries constant Greg KH <gregkh@linuxfoundation.org> - 2017-01-17 08:20 +0100
        Re: [PATCH 2/3] Make static usermode helper binaries constant "J. Bruce Fields" <bfields@fieldses.org> - 2017-01-17 16:20 +0100
          Re: [PATCH 2/3] Make static usermode helper binaries constant Greg KH <gregkh@linuxfoundation.org> - 2017-01-17 16:30 +0100
            Re: [kernel-hardening] Re: [PATCH 2/3] Make static usermode helper  binaries constant Greg KH <gregkh@linuxfoundation.org> - 2017-01-19 13:10 +0100
              Re: [kernel-hardening] Re: [PATCH 2/3] Make static usermode helper  binaries constant "J. Bruce Fields" <bfields@fieldses.org> - 2017-01-19 17:30 +0100
    Re: [PATCH 2/3] Make static usermode helper binaries constant Jeff Layton <jlayton@poochiereds.net> - 2017-01-17 16:50 +0100
      Re: [PATCH 2/3] Make static usermode helper binaries constant Greg KH <gregkh@linuxfoundation.org> - 2017-01-17 17:00 +0100
        Re: [PATCH 2/3] Make static usermode helper binaries constant Jeff Layton <jlayton@poochiereds.net> - 2017-01-17 17:10 +0100
          Re: [PATCH 2/3] Make static usermode helper binaries constant Greg KH <gregkh@linuxfoundation.org> - 2017-01-17 17:20 +0100
  [PATCH 1/3] kmod: make usermodehelper path a const string Greg KH <gregkh@linuxfoundation.org> - 2017-01-16 18:00 +0100
  Re: [PATCH 0/4] make call_usermodehelper a bit more "safe" Greg KH <gregkh@linuxfoundation.org> - 2017-01-16 18:00 +0100
  [PATCH 3/3] Introduce STATIC_USERMODEHELPER to mediate  call_usermodehelper() Greg KH <gregkh@linuxfoundation.org> - 2017-01-16 18:00 +0100
    Re: [PATCH 3/3] Introduce STATIC_USERMODEHELPER to mediate  call_usermodehelper() Jeff Layton <jlayton@poochiereds.net> - 2017-01-17 17:30 +0100
      Re: [PATCH 3/3] Introduce STATIC_USERMODEHELPER to mediate  call_usermodehelper() Greg KH <gregkh@linuxfoundation.org> - 2017-01-17 17:40 +0100
        Re: [PATCH 3/3] Introduce STATIC_USERMODEHELPER to mediate  call_usermodehelper() Jeff Layton <jlayton@poochiereds.net> - 2017-01-17 18:00 +0100
  Re: [PATCH 0/4] make call_usermodehelper a bit more "safe" Kees Cook <keescook@chromium.org> - 2017-01-17 18:30 +0100

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