[patch] libstdc++/65142 Check read() result in std::random_device.

[Jonathan Wakely]

On 11/09/15 14:44 +0100, Jonathan Wakely wrote:
>We should not silently ignore a failure to read from the random
>device.
>
>Tested powerpc64le-linux, committed to trunk. I'm going to commit this
>to the gcc-5 branch too.
>
>

>commit 2d2f7012dc3744dafef0de94dd845bd190253dbd
>Author: Jonathan Wakely <jwakely@redhat.com>
>Date:   Fri Feb 20 17:29:50 2015 +0000
>
>    Check read() result in std::random_device.
>    
>    	PR libstdc++/65142
>    	* src/c++11/random.cc (random_device::_M_getval()): Check read result.
>
>diff --git a/libstdc++-v3/src/c++11/random.cc b/libstdc++-v3/src/c++11/random.cc
>index edf900f..1d102c7 100644
>--- a/libstdc++-v3/src/c++11/random.cc
>+++ b/libstdc++-v3/src/c++11/random.cc
>@@ -130,13 +130,17 @@ namespace std _GLIBCXX_VISIBILITY(default)
> #endif
> 
>     result_type __ret;
>+
> #ifdef _GLIBCXX_HAVE_UNISTD_H
>-    read(fileno(static_cast<FILE*>(_M_file)),
>-	 static_cast<void*>(&__ret), sizeof(result_type));
>+    auto e = read(fileno(static_cast<FILE*>(_M_file)),
>+		  static_cast<void*>(&__ret), sizeof(result_type));
> #else
>-    std::fread(static_cast<void*>(&__ret), sizeof(result_type),
>-	       1, static_cast<FILE*>(_M_file));
>+    auto e = std::fread(static_cast<void*>(&__ret), sizeof(result_type),
>+		        1, static_cast<FILE*>(_M_file));
> #endif
>+    if (e != sizeof(result_type))
>+      __throw_runtime_error(__N("random_device could not read enough bytes"));
>+
>     return __ret;
>   }
> 

Florian pointed out that this code should handle short reads (or
EINTR) by retrying in a loop, so here's another attempt to fix it.

This also fixes the bug I introduced in the std::fread() case where it
expects e == sizeof(result_type) but fread will only return 0 or 1.

We could loop in the fread case too, but I'm not doing that. If
someone on non-POSIX targets cares enough they can make that change
later.

Any comments on this version?

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