[PATCH] PR libstdc++/87787 avoid undefined null args to memcpy and memmove

[Jonathan Wakely]

The C++ char_traits and ctype APIs do not disallow null pointer
arguments, so we need explicit checks to ensure we don't forward null
pointers to memcpy or memmove.

        PR libstdc++/87787
        * include/bits/char_traits.h (char_traits::move): Do not pass null
        pointers to memmove.
        * include/bits/locale_facets.h
        (ctype<char>::widen(const char*, const char*, char*)): Do not
        pass null pointers to memcpy.
        (ctype<char>::narrow(const char*, const char*, char, char*)):
        Likewise.
        (ctype<char>::do_widen(const char*, const char*, char*)):
        Likewise.
        (ctype<char>::do_narrow(const char*, const char*, char, char*)):
        Likewise.

Tested powerpc64-linux, committed to trunk.



commit 8322b49ba9dfa3cef33a78e4bc2bab0937c3849a
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Mon Jan 7 14:38:22 2019 +0000

    PR libstdc++/87787 avoid undefined null args to memcpy and memmove
    
    The C++ char_traits and ctype APIs do not disallow null pointer
    arguments, so we need explicit checks to ensure we don't forward null
    pointers to memcpy or memmove.
    
            PR libstdc++/87787
            * include/bits/char_traits.h (char_traits::move): Do not pass null
            pointers to memmove.
            * include/bits/locale_facets.h
            (ctype<char>::widen(const char*, const char*, char*)): Do not
            pass null pointers to memcpy.
            (ctype<char>::narrow(const char*, const char*, char, char*)):
            Likewise.
            (ctype<char>::do_widen(const char*, const char*, char*)):
            Likewise.
            (ctype<char>::do_narrow(const char*, const char*, char, char*)):
            Likewise.

diff --git a/libstdc++-v3/include/bits/char_traits.h 
b/libstdc++-v3/include/bits/char_traits.h
index a2ba5da910f..06e04ceaa34 100644
--- a/libstdc++-v3/include/bits/char_traits.h
+++ b/libstdc++-v3/include/bits/char_traits.h
@@ -183,6 +183,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     char_traits<_CharT>::
     move(char_type* __s1, const char_type* __s2, std::size_t __n)
     {
+      if (__n == 0)
+       return __s1;
       return static_cast<_CharT*>(__builtin_memmove(__s1, __s2,
                                                    __n * sizeof(char_type)));
     }
diff --git a/libstdc++-v3/include/bits/locale_facets.h 
b/libstdc++-v3/include/bits/locale_facets.h
index 33cff652222..66ac9c07a5d 100644
--- a/libstdc++-v3/include/bits/locale_facets.h
+++ b/libstdc++-v3/include/bits/locale_facets.h
@@ -896,7 +896,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
        if (_M_widen_ok == 1)
          {
-           __builtin_memcpy(__to, __lo, __hi - __lo);
+           if (__builtin_expect(__hi != __lo, true))
+             __builtin_memcpy(__to, __lo, __hi - __lo);
            return __hi;
          }
        if (!_M_widen_ok)
@@ -961,7 +962,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       {
        if (__builtin_expect(_M_narrow_ok == 1, true))
          {
-           __builtin_memcpy(__to, __lo, __hi - __lo);
+           if (__builtin_expect(__hi != __lo, true))
+             __builtin_memcpy(__to, __lo, __hi - __lo);
            return __hi;
          }
        if (!_M_narrow_ok)
@@ -1100,7 +1102,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       virtual const char*
       do_widen(const char* __lo, const char* __hi, char_type* __to) const
       {
-       __builtin_memcpy(__to, __lo, __hi - __lo);
+       if (__builtin_expect(__hi != __lo, true))
+         __builtin_memcpy(__to, __lo, __hi - __lo);
        return __hi;
       }
 
@@ -1153,7 +1156,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       do_narrow(const char_type* __lo, const char_type* __hi,
                char __dfault __attribute__((__unused__)), char* __to) const
       {
-       __builtin_memcpy(__to, __lo, __hi - __lo);
+       if (__builtin_expect(__hi != __lo, true))
+         __builtin_memcpy(__to, __lo, __hi - __lo);
        return __hi;
       }