gEDA-bug: [Bug 700194] Re: gsch2pcb `gnetlist-arg' in project file can lead to arbitrary code execution.

[Peter Clifton <pcjc2@xxxxxxxxx>]

What is really scary about yuor example is that gschem is so silent when
loading the malicious code.

See the gsch2pcb-700194/-l,-m/one.sch example.

NOTHING is printed in the schem log, and it treats the schematic as if
it were a blank file. (Which it otherwise is).

On the console we have:

Read garbage in [/home/pcjc2/gsch2pcb-700194/-l,-m/one.sch] :
>>
(display "Arbitrary code (1)\n")
<<

This would not be seen if running via xgsch2pcb, or loading the
schematic from a copy of gschem started from a GUI environment.

-- 
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https://bugs.launchpad.net/bugs/700194

Title:
  gsch2pcb `gnetlist-arg' in project file can lead to arbitrary code execution.

Status in GPL Electronic Design Automation tools:
  Fix Committed
Status in âgeda-gafâ package in Ubuntu:
  New

Bug description:
   affects geda
 tag gsch2pcb
 security yes
 done

The `--gnetlist-arg' option to gsch2pcb is used to pass arbitrary
arguments to gnetlist.  This option can also be provided in a project
file.

This option can allow arbitrary code execution via a maliciously crafted
project file and/or schematics, by several possible vectors.

The most blatant is direct Scheme code execution:

  gnetlist-arg "-c (display 'EVIL) (newline)"

Of middling deviousness is execution of Scheme programs disguised as
schematics:

  gnetlist-arg -minnocuous.sch
  gnetlist-arg -lharmless.sch

Most subtle is manipulation of the Scheme load path via the -L option:

  gnetlist-arg -L.

If a file called `gnetlist' is placed in the same directory as
`evil.project' (easily confused with `gnetlistrc' by the hapless user),
it will be loaded in preference to `gnetlist.scm' installed with gEDA
and always loaded during gnetlist initialisation.

These attacks can all be easily reproduced.

Because gsch2pcb project files are usually considered in the minds of
users to be datafiles, this option (which would be fine if present in a
Makefile or some other file normally considered as an executed file) is
a security risk.

Recommended fix: `--gnetlist-arg' option should be disallowed in
gsch2pcb project files.  The only "legitimate" gnetlist command-line
option it enables is `-O' (for passing backend options), and none of the
backends used by gsch2pcb currently take any options.





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