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Re: [patch] libstdc++/65142 Check read() result in std::random_device.
- From: Jonathan Wakely <jwakely at redhat dot com>
- To: libstdc++ at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Tue, 15 Sep 2015 12:47:13 +0100
- Subject: Re: [patch] libstdc++/65142 Check read() result in std::random_device.
- Authentication-results: sourceware.org; auth=none
- References: <20150911134418 dot GK2631 at redhat dot com>
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?
commit 6700c8c652da94332562fff465a1569d8fa9c94d
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Sep 15 11:02:42 2015 +0100
Fix handling of short reads in std::random_device
PR libstdc++/65142
* src/c++11/random.cc (random_device::_M_getval()): Retry after short
reads.
diff --git a/libstdc++-v3/src/c++11/random.cc b/libstdc++-v3/src/c++11/random.cc
index 1d102c7..f1d6125 100644
--- a/libstdc++-v3/src/c++11/random.cc
+++ b/libstdc++-v3/src/c++11/random.cc
@@ -130,16 +130,26 @@ namespace std _GLIBCXX_VISIBILITY(default)
#endif
result_type __ret;
-
+ void* p = &__ret;
+ size_t n = sizeof(result_type);
#ifdef _GLIBCXX_HAVE_UNISTD_H
- auto e = read(fileno(static_cast<FILE*>(_M_file)),
- static_cast<void*>(&__ret), sizeof(result_type));
+ do
+ {
+ const int e = read(fileno(static_cast<FILE*>(_M_file)), p, n);
+ if (e > 0)
+ {
+ n -= e;
+ p = static_cast<char*>(p) + e;
+ }
+ else if (e != -1 || errno != EINTR)
+ __throw_runtime_error(__N("random_device could not be read"));
+ }
+ while (n > 0);
#else
- auto e = std::fread(static_cast<void*>(&__ret), sizeof(result_type),
- 1, static_cast<FILE*>(_M_file));
+ const size_t e = std::fread(p, n, 1, static_cast<FILE*>(_M_file));
+ if (e != 1)
+ __throw_runtime_error(__N("random_device could not be read"));
#endif
- if (e != sizeof(result_type))
- __throw_runtime_error(__N("random_device could not read enough bytes"));
return __ret;
}