Fix a bug in wcsnrtombs

__d is a char * destination buffer, so __b is already the byte capacity.
Dividing by sizeof(wchar_t) makes no sense here, it was likely copy-pasted
from mbsnrtowcs (where the destination is wchar_t *). The first branch also
fails to limit __n (the byte write cap) to __b, so overflows are possible when
a wide character produces multi-byte output. The second branch (else) correctly
limits __n to __b.

This commit replaces the broken two-branch logic with the simple correct
pattern matching wcsrtombs, and adds two tests two prove that nothing broke.

1 files changed, 3 insertions, 10 deletions

diff --git a/include/wchar.h b/include/wchar.h
index a840f1a..0842115 100644
--- a/include/wchar.h
+++ b/include/wchar.h
@@ -190,16 +190,9 @@ _FORTIFY_FN(wcsnrtombs) size_t wcsnrtombs(char * _FORTIFY_POS0 __d,
         size_t __b = __bos(__d, 0);
         size_t __r;
 
-        if (__wn > __n / sizeof(wchar_t)) {
-                __b /= sizeof(wchar_t);
-                __r = __orig_wcsnrtombs(__d, __s, __wn > __b ? __b : __wn, __n, __st);
-                if (__b < __wn && __d && *__s && __r != (size_t)-1)
-                        __builtin_trap();
-        } else {
-                __r = __orig_wcsnrtombs(__d, __s, __wn, __n > __b ? __b : __n, __st);
-                if (__b < __n && __d && *__s && __r != (size_t)-1)
-                        __builtin_trap();
-        }
+        __r = __orig_wcsnrtombs(__d, __s, __wn, __n > __b ? __b : __n, __st);
+        if (__b < __n && __d && *__s && __r != (size_t)-1)
+                __builtin_trap();
         return __r;
 }
 #endif