[Qemu-devel] [PATCH v2 3/3] qapi: Fix memleak in string visitors on int lists

[Eric Blake <eblake@redhat.com>]

Commit 7f8f9ef1 introduced the ability to store a list of
integers as a sorted list of ranges, but when merging ranges,
it leaks one or more ranges.  It was also using range_get_last()
incorrectly within range_compare() (a range is a start/end pair,
but range_get_last() is for start/len pairs), and will also
mishandle a range ending in UINT64_MAX (remember, we document
that no range covers 2**64 bytes, but that ranges that end on
UINT64_MAX have end < begin).

The whole merge algorithm was rather complex, and included
unnecessary passes over data within glib functions, and enough
indirection to make it hard to easily plug the data leaks.
Since we are already hard-coding things to a list of ranges,
just rewrite the thing to open-code the traversal and
comparisons, by making the range_compare() helper function give
us an answer that is easier to use, at which point we avoid the
need to pass any callbacks to g_list_*(). Then by reusing
range_extend() instead of duplicating effort with range_merge(),
we cover the corner cases correctly.

Drop the now-unused range_merge() and ranges_can_merge().

Doing this lets test-string-{input,output}-visitor pass under
valgrind without leaks.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 util/range.c | 75 +++++++++++++++++++++++-------------------------------------
 1 file changed, 29 insertions(+), 46 deletions(-)

diff --git a/util/range.c b/util/range.c
index dd46092..56e6baf 100644
--- a/util/range.c
+++ b/util/range.c
@@ -28,65 +28,48 @@
  *   - this can not represent a full 0 to ~0x0LL range.
  */

-/* 0,1 can merge with 1,2 but don't overlap */
-static bool ranges_can_merge(Range *range1, Range *range2)
+/* Return -1 if @a < @b, 1 if greater, and 0 if they touch or overlap. */
+static inline int range_compare(Range *a, Range *b)
 {
-    return !(range1->end < range2->begin || range2->end < range1->begin);
-}
-
-static void range_merge(Range *range1, Range *range2)
-{
-    if (range1->end < range2->end) {
-        range1->end = range2->end;
-    }
-    if (range1->begin > range2->begin) {
-        range1->begin = range2->begin;
-    }
-}
-
-static gint range_compare(gconstpointer a, gconstpointer b)
-{
-    Range *ra = (Range *)a, *rb = (Range *)b;
-    if (ra->begin == rb->begin && ra->end == rb->end) {
-        return 0;
-    } else if (range_get_last(ra->begin, ra->end) <
-               range_get_last(rb->begin, rb->end)) {
+    /* Zero a->end is 2**64, and therefore not less than any b->begin */
+    if (a->end && a->end < b->begin) {
         return -1;
-    } else {
+    }
+    if (b->end && a->begin > b->end) {
         return 1;
     }
+    return 0;
 }

+/* Insert @data into @list of ranges; caller no longer owns @data */
 GList *range_list_insert(GList *list, Range *data)
 {
-    GList *l, *next = NULL;
-    Range *r, *nextr;
+    GList *l;

-    if (!list) {
-        list = g_list_insert_sorted(list, data, range_compare);
-        return list;
+    /* Range lists require no empty ranges */
+    assert(data->begin < data->end || (data->begin && !data->end));
+
+    for (l = list; l && range_compare(l->data, data) < 0; l = l->next) {
+        /* Skip all list elements strictly less than data */
     }

-    nextr = data;
-    l = list;
-    while (l && l != next && nextr) {
-        r = l->data;
-        if (ranges_can_merge(r, nextr)) {
-            range_merge(r, nextr);
-            l = g_list_remove_link(l, next);
-            next = g_list_next(l);
-            if (next) {
-                nextr = next->data;
-            } else {
-                nextr = NULL;
-            }
-        } else {
-            l = g_list_next(l);
-        }
+    if (!l || range_compare(l->data, data) > 0) {
+        /* Rest of the list (if any) is strictly greater than @data */
+        return g_list_insert_before(list, l, data);
     }

-    if (!l) {
-        list = g_list_insert_sorted(list, data, range_compare);
+    /* Current list element overlaps @data, merge the two */
+    range_extend(l->data, data);
+    g_free(data);
+
+    /* Merge any subsequent list elements that now also overlap */
+    while (l->next && range_compare(l->data, l->next->data) == 0) {
+        GList *new_l;
+
+        range_extend(l->data, l->next->data);
+        g_free(l->next->data);
+        new_l = g_list_delete_link(list, l->next);
+        assert(new_l == list);
     }

     return list;
-- 
2.5.5