[PATCH] tr: fix crash validating -c with some case char classes

[Pádraig Brady]

This crash was identified by Cyber Independent Testing Lab:
https://cyber-itl.org/2020/10/28/citl-7000-defects.html
and was introduced with commit v8.5-163-g3f48829c2

* src/tr.c (validate_case_classes): Don't apply these
extra case alignment checks in the --complement case,
which is even more restrictive as to the contents of SET2.
* tests/misc/tr-case-class.sh: Add a test case,
for a large SET1, which caused the length adjustment
in validate_case_classes to underflow and trigger the assert.
* NEWS: Mention the bug fix.
---
 NEWS                        | 4 ++++
 src/tr.c                    | 2 +-
 tests/misc/tr-case-class.sh | 3 +++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index 657477ac7..61b5d42f6 100644
--- a/NEWS
+++ b/NEWS
@@ -20,6 +20,10 @@ GNU coreutils NEWS                                    -*- 
outline -*-
   ls no longer crashes when printing the SELinux context for unstatable files.
   [bug introduced in coreutils-6.9.91]
 
+  tr no longer crashes when using --complement with certain
+  invalid combinations of case character classes.
+  [bug introduced in coreutils-8.6]
+
 ** Changes in behavior
 
   cp and install now default to copy-on-write (COW) if available.
diff --git a/src/tr.c b/src/tr.c
index 6f7650764..94794a28e 100644
--- a/src/tr.c
+++ b/src/tr.c
@@ -1176,7 +1176,7 @@ validate_case_classes (struct Spec_list *s1, struct 
Spec_list *s2)
   bool s1_new_element = true;
   bool s2_new_element = true;
 
-  if (!s2->has_char_class)
+  if (complement || !s2->has_char_class)
     return;
 
   for (int i = 0; i < N_CHARS; i++)
diff --git a/tests/misc/tr-case-class.sh b/tests/misc/tr-case-class.sh
index 470197ee3..9f442c029 100755
--- a/tests/misc/tr-case-class.sh
+++ b/tests/misc/tr-case-class.sh
@@ -110,4 +110,7 @@ the latter string must not end with a character class' > exp
   compare exp out || fail=1
 fi
 
+# coreutils 8.6 - 8.32 inclusive, would abort trying to validate the following
+returns_ 1 tr -c '[:upper:]\000-\370' '[:lower:]' < /dev/null || fail=1
+
 Exit $fail
-- 
2.26.2