Crash on invalid `astr` attribute parameter index [codex]

[mgordon]

CodeHawk-C crash on invalid astr attribute parameter index

Summary

While analyzing SPEC CPU 2017 538.imagick_r, CodeHawk-C crashed during
project linking before analysis rounds started. The crash occurs when a parsed
star attribute parameter (astr) references an attrparam-table index that does
not exist in the current file dictionary.

The immediate crash was:

chc.util.IndexedTable.IndexedTableError:
Unable to retrieve item 5 from table attrparam-table (size: 4)

The stack goes through:

CLinker.link_varinfos
CGlobalDeclarations.make_global_varinfo
CTyp.strip_attributes
CAttributes.__str__
CAttribute.__str__
CAttrStar.__str__
CAttrStar.param
CDictionary.get_attrparam

Reproducer

Use repros/imagick-invalid-astr-attrparam.c:

#include <stdio.h>
#include <stdlib.h>

void *repro_alloc(size_t n) {
  return malloc(n);
}

int main(void) {
  void *p = repro_alloc(16);
  puts(p == NULL ? "null" : "ok");
  free(p);
  return 0;
}

Analyze this file as a small CodeHawk-C project with ordinary glibc headers.
The same malformed astr dictionary shape is observed in the imagick parse
results for files such as:

magick/quantum/quantum_cdict.xml:
  attrparam-table has max index 4
  attrparam ix=2 has t="astr" and a="5"

Several other imagick files have astr entries whose argument is clearly not a
valid local attrparam-table index, e.g. a="431" with max attrparam index 5.

Cause

CAttrStar.param assumes that args[0] is always an attrparam-table index. In
these parsed GNU/glibc attribute cases that assumption is false, so stringifying
type attributes during strip_attributes can chase an invalid dictionary index.

There is also a small type mismatch in CAttrStar.__str__: it compares
self.index to self.args[0], but self.index is an integer and
self.args[0] is a string. The self-reference case therefore never matches.

Minimal Fix

Treat self-referential or invalid astr arguments as opaque star attributes
instead of chasing the bad dictionary index. This is conservative for analysis:
the exact GNU attribute expression is not needed for PTSan/CodeHawk memory
proof obligations in imagick, and dropping precision in this attribute string
avoids blocking project analysis.

The local patch:

CodeHawk-C/chc/app/CAttributes.py

changes CAttrStar.param to catch IndexedTableError and return self, and
fixes __str__ to compare self.index with int(self.args[0]).

imagick-invalid-astr-attrparam.c