libstdc++: Fix undefined behaviour in random dist serialization (PR93205)

The deserialization functions for random number distributions fail to
check the stream state before using the extracted values. In some cases
this leads to using indeterminate values to resize a vector, and then
filling that vector with indeterminate values.

No values that affect control flow should be used without checking that a
good value was read from the stream.

Additionally, where reasonable to do so, defer modifying any state in
the distribution until all values have been successfully read, to avoid
modifying some of the distribution's parameters and leaving others
unchanged.

	PR libstdc++/93205
	* include/bits/random.h (operator>>): Check stream operation succeeds.
	* include/bits/random.tcc (operator<<): Remove redundant __ostream_type
	typedefs.
	(operator>>): Remove redundant __istream_type typedefs. Check stream
	operations succeed.
	(__extract_params): New function to fill a vector from a stream.
	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error line.

From-SVN: r280061

libstdc++-v3/ChangeLog

 2020-01-09  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/93205
+	* include/bits/random.h (operator>>): Check stream operation succeeds.
+	* include/bits/random.tcc (operator<<): Remove redundant __ostream_type
+	typedefs.
+	(operator>>): Remove redundant __istream_type typedefs. Check stream
+	operations succeed.
+	(__extract_params): New function to fill a vector from a stream.
+	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error line.
+
 	PR libstdc++/93208
 	* config/abi/pre/gnu.ver: Add new exports.
 	* include/std/memory_resource (memory_resource::~memory_resource()):

libstdc++-v3/include/bits/random.h

@@ -3720,13 +3720,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    * @returns The input stream with @p __x extracted or in an error state.
    */
   template<typename _CharT, typename _Traits>
-    std::basic_istream<_CharT, _Traits>&
+    inline std::basic_istream<_CharT, _Traits>&
     operator>>(std::basic_istream<_CharT, _Traits>& __is,
 	       std::bernoulli_distribution& __x)
     {
       double __p;
-      __is >> __p;
-      __x.param(bernoulli_distribution::param_type(__p));
+      if (__is >> __p)
+	__x.param(bernoulli_distribution::param_type(__p));
       return __is;
     }
 

libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc

@@ -12,4 +12,4 @@ auto x = std::generate_canonical<std::size_t,
 
 // { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 171 }
 
-// { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 3320 }
+// { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 3281 }