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Description of problem:
The _PySequence_BytesToCharpArray function in the C portion of the python module contains a triggerable integer wraparound which leads to a heap overflow. This is only appears to be triggerable via rather strange/contrived usage of the module, but should still be fixed in case another method is discovered that leads to triggering it.


Version-Release number of selected component (if applicable):
At least 3.2.6 - > 3.5.2. May be in earlier versions, I did not check.

How reproducible:
100%

Steps to Reproduce:
1. Boot a 32bit system.
2. import subprocess32 as subprocess
subprocess._posixsubprocess.fork_exec("a",'a'*0x3FFFFFFF,"a",set(),"a","a",1,1,1,1,1,1,1,3,1,1,"a")

Actual results:
*** glibc detected *** /usr/bin/python: double free or corruption (!prev): 0x09464b38 ***
Segmentation fault (core dumped)

Expected results:
Error message.

Additional info:
Upstream issue: https://github.com/google/python-subprocess32/issues/54
Upstream fix: https://github.com/google/python-subprocess32/pull/55

Created attachment 1477908 [details]
Backport of upstream patch

I've created a backport of the upstream fix.

> Upstream issue: https://github.com/google/python-subprocess32/issues/54
> Upstream fix: https://github.com/google/python-subprocess32/pull/55

The fix is now merged and subprocess32 version 3.5.3 has been released with the fix.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2019:2036