patch 9.1.0089: qsort() comparison functions should be transitive

Problem:  qsort() comparison functions should be transitive
Solution: Do not subtract values, but rather use explicit comparisons

Improve qsort() comparison functions

There has been a recent report on qsort() causing out-of-bounds read &
write in glibc for non transitive comparison functions
https://www.qualys.com/2024/01/30/qsort.txt

Even so the bug is in glibc's implementation of the qsort() algorithm,
it's bad style to just use substraction for the comparison functions,
which may cause overflow issues and as hinted at in OpenBSD's manual
page for qsort(): "It is almost always an error to use subtraction to
compute the return value of the comparison function."

So check the qsort() comparison functions and change them to be safe.

closes: #13980

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/ex_cmds.c

@@ -323,7 +323,7 @@ sort_compare(const void *s1, const void *s2)
     if (sort_nr)
     {
 	if (l1.st_u.num.is_number != l2.st_u.num.is_number)
-	    result = l1.st_u.num.is_number - l2.st_u.num.is_number;
+	    result = l1.st_u.num.is_number > l2.st_u.num.is_number ? 1 : -1;
 	else
 	    result = l1.st_u.num.value == l2.st_u.num.value ? 0
 			     : l1.st_u.num.value > l2.st_u.num.value ? 1 : -1;

src/mbyte.c

@@ -5613,7 +5613,8 @@ tv_nr_compare(const void *a1, const void *a2)
     listitem_T *li1 = *(listitem_T **)a1;
     listitem_T *li2 = *(listitem_T **)a2;
 
-    return li1->li_tv.vval.v_number - li2->li_tv.vval.v_number;
+    return li1->li_tv.vval.v_number == li2->li_tv.vval.v_number ? 0 :
+	li1->li_tv.vval.v_number > li2->li_tv.vval.v_number ? 1 : -1;
 }
 
     void

src/profiler.c

@@ -287,11 +287,13 @@ profile_equal(proftime_T *tm1, proftime_T *tm2)
 profile_cmp(const proftime_T *tm1, const proftime_T *tm2)
 {
 # ifdef MSWIN
-    return (int)(tm2->QuadPart - tm1->QuadPart);
+    return tm2->QuadPart == tm1->QuadPart ? 0 :
+	tm2->QuadPart > tm1->QuadPart ? 1 : -1;
 # else
     if (tm1->tv_sec == tm2->tv_sec)
-	return tm2->tv_fsec - tm1->tv_fsec;
+	return tm2->tv_fsec == tm1->tv_fsec ? 0 :
-    return tm2->tv_sec - tm1->tv_sec;
+	    tm2->tv_fsec > tm1->tv_fsec ? 1 : -1;
+    return tm2->tv_sec > tm1->tv_sec ? 1 : -1;
 # endif
 }
 

src/search.c

@@ -4908,7 +4908,10 @@ fuzzy_match_str_compare(const void *s1, const void *s2)
     int		idx1 = ((fuzmatch_str_T *)s1)->idx;
     int		idx2 = ((fuzmatch_str_T *)s2)->idx;
 
-    return v1 == v2 ? (idx1 - idx2) : v1 > v2 ? -1 : 1;
+    if (v1 == v2)
+	return idx1 == idx2 ? 0 : idx1 > idx2 ? 1 : -1;
+    else
+	return v1 > v2 ? -1 : 1;
 }
 
 /*
@@ -4936,9 +4939,14 @@ fuzzy_match_func_compare(const void *s1, const void *s2)
     char_u	*str1 = ((fuzmatch_str_T *)s1)->str;
     char_u	*str2 = ((fuzmatch_str_T *)s2)->str;
 
-    if (*str1 != '<' && *str2 == '<') return -1;
+    if (*str1 != '<' && *str2 == '<')
-    if (*str1 == '<' && *str2 != '<') return 1;
+	return -1;
-    return v1 == v2 ? (idx1 - idx2) : v1 > v2 ? -1 : 1;
+    if (*str1 == '<' && *str2 != '<')
+	return 1;
+    if (v1 == v2)
+	return idx1 == idx2 ? 0 : idx1 > idx2 ? 1 : -1;
+    else
+	return v1 > v2 ? -1 : 1;
 }
 
 /*

src/spellsuggest.c

@@ -3763,11 +3763,16 @@ sug_compare(const void *s1, const void *s2)
 {
     suggest_T	*p1 = (suggest_T *)s1;
     suggest_T	*p2 = (suggest_T *)s2;
-    int		n = p1->st_score - p2->st_score;
+    int		n;
+
+    n = p1->st_score == p2->st_score ? 0 :
+	p1->st_score > p2->st_score ? 1 : -1;
 
     if (n == 0)
     {
-	n = p1->st_altscore - p2->st_altscore;
+	n = p1->st_altscore == p2->st_altscore ? 0 :
+	    p1->st_altscore > p2->st_altscore ? 1 : -1;
+
 	if (n == 0)
 	    n = STRICMP(p1->st_word, p2->st_word);
     }

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    89,
 /**/
     88,
 /**/

src/window.c

@@ -7753,9 +7753,15 @@ frame_check_width(frame_T *topfrp, int width)
  * Simple int comparison function for use with qsort()
  */
     static int
-int_cmp(const void *a, const void *b)
+int_cmp(const void *pa, const void *pb)
 {
-    return *(const int *)a - *(const int *)b;
+    const int a = *(const int *)pa;
+    const int b = *(const int *)pb;
+    if (a > b)
+	return 1;
+    if (a < b)
+	return -1;
+    return 0;
 }
 
 /*