Fix CVE-2022-24795

There was an integer overflow in yajl_buf_ensure_available() leading
to allocating less memory than requested. Then data were written past
the allocated heap buffer in yajl_buf_append(), the only caller of
yajl_buf_ensure_available(). Another result of the overflow was an
infinite loop without a return from yajl_buf_ensure_available().

yajl-ruby project, which bundles yajl, fixed it
<brianmario/yajl-ruby#211> by checking for the
integer overflow, fortifying buffer allocations, and report the
failures to a caller. But then the caller yajl_buf_append() skips
a memory write if yajl_buf_ensure_available() failed leading to a data
corruption.

A yajl fork mainter recommended calling memory allocation callbacks with
the large memory request and let them to handle it. But that has the
problem that it's not possible pass the overely large size to the
callbacks.

This patch catches the integer overflow and terminates the process
with abort().

GHSA-jj47-x69x-mxrm

Origin: ppisar/yajl@23cea2d
Bug: lloyd/yajl#239
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1040036

Author: ppisar

src/cdogs/yajl/yajl_buf.c

@@ -45,7 +45,17 @@ void yajl_buf_ensure_available(yajl_buf buf, size_t want)
 
     need = buf->len;
 
-    while (want >= (need - buf->used)) need <<= 1;
+    if (((buf->used > want) ? buf->used : want) > (size_t)(buf->used + want)) {
+        /* We cannot allocate more memory than SIZE_MAX. */
+        abort();
+    }
+    while (want >= (need - buf->used)) {
+        if (need >= (size_t)((size_t)(-1)<<1)>>1) {
+            /* need would overflow. */
+            abort();
+        }
+        need <<= 1;
+    }
 
     if (need != buf->len) {
         buf->data = (unsigned char *) YA_REALLOC(buf->alloc, buf->data, need);