Fix OOB read in stdlib thousand grouping parsing [BZ #29727]

__correctly_grouped_prefixmb only worked with thousands_len == 1,
otherwise it read past the end of cp or thousands.

This affects scanf formats like %'d, %'f and the internal but
exposed __strto{l,ul,f,d,..}_internal with grouping flag set
and an LC_NUMERIC locale where thousands_len > 1.

Avoid OOB access by considering thousands_len when initializing cp.
This fixes bug 29727.

Found by the morello port with strict bounds checking where

FAIL: stdlib/tst-strtod4
FAIL: stdlib/tst-strtod5i

crashed using a locale with thousands_len==3.

diff --git a/stdlib/grouping.c b/stdlib/grouping.c
index be7922f5fdcd1e12c97d916969dd8e5e77dba2f1..462289748811427570b7e9571f89f1b633534aaa 100644 (file)
--- a/stdlib/grouping.c
+++ b/stdlib/grouping.c
@@ -64,9 +64,17 @@ __correctly_grouped_prefixmb (const STRING_TYPE *begin, const STRING_TYPE *end,
   thousands_len = strlen (thousands);
 #endif
 
+#ifdef USE_WIDE_CHAR
   while (end > begin)
+#else
+  while (end - begin >= thousands_len)
+#endif
     {
+#ifdef USE_WIDE_CHAR
       const STRING_TYPE *cp = end - 1;
+#else
+      const STRING_TYPE *cp = end - thousands_len;
+#endif
       const char *gp = grouping;
 
       /* Check first group.  */