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0015976

CMake

public

2016-02-16 20:26

2016-06-10 14:21

Reporter

Cristian Rodríguez

Assigned To

Brad King

Priority

normal

Severity

minor

Reproducibility

always

Status

closed

Resolution

fixed

Platform

linux

OS Version

any

Product Version

CMake 3.4.3

Target Version

CMake 3.6

Fixed in Version

CMake 3.6

Summary

0015976: cmSystemTools::RandomSeed() requests excessive entropy per invocation

Description

cmSystemTools::RandomSeed() opens a *buffered* ifstream, the final result is that each invocation requests _IO_BUFSIZ -1 of entropy to the operating system instead of just sizeof(seed)

Steps To Reproduce

mkdir test_cmake
echo "PROJECT(foo)" > CMakeLists.txt
cd test_cmake
strace -f -ocmake.trace cmake .

open cmake.trace

10768 26289 open("/dev/urandom", O_RDONLY) = 4
10769 26289 read(4, "h\304j\vx\314\26\0042\250g\275\0014,\256\251\257T&\304\212\310\347q\201\263\324\330\273z8"..., 8191) = 8191
10770 26289 close(4) = 0
10771 26289 write(3, "cmake_minimum_required(VERSION 3"..., 795) = 795
10772 26289 close(3) = 0
10773 26289 stat("/home/crrodriguez/test_cmake/CMakeFiles/CMakeTmp", {st_mode=S_IFDIR|0755, st_size=58, ...}) = 0
10774 26289 getcwd("/home/crrodriguez/test_cmake", 2048) = 29

Additional Information

git diff
diff --git a/Source/cmSystemTools.cxx b/Source/cmSystemTools.cxx
index 3ba7287..26bec34 100644
--- a/Source/cmSystemTools.cxx
+++ b/Source/cmSystemTools.cxx
@@ -2184,8 +2184,10 @@ unsigned int cmSystemTools::RandomSeed()
   } seed;

   // Try using a real random source.
- cmsys::ifstream fin("/dev/urandom");
- if(fin && fin.read(seed.bytes, sizeof(seed)) &&
+ cmsys::ifstream fin;
+ fin.rdbuf()->pubsetbuf(0, 0);
+ fin.open("/dev/urandom");
+ if(fin.good() && fin.read(seed.bytes, sizeof(seed)) &&
      fin.gcount() == sizeof(seed))
     {
     return seed.integer;

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Notes
(0040496) Brad King (manager) 2016-02-17 09:05 edited on: 2016-02-19 09:45	Good catch, thanks! Applied: cmSystemTools: Avoid excess entropy consumption by RandomSeed https://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=f23f18ab [^]

(0041244) Kitware Robot (administrator) 2016-06-10 14:21	This issue tracker is no longer used. Further discussion of this issue may take place in the current CMake Issues page linked in the banner at the top of this page.

Issue History
Date Modified	Username	Field	Change
2016-02-16 20:26	Cristian Rodríguez	New Issue
2016-02-17 09:05	Brad King	Note Added: 0040496
2016-02-17 09:05	Brad King	Assigned To	=> Brad King
2016-02-17 09:05	Brad King	Status	new => resolved
2016-02-17 09:05	Brad King	Resolution	open => fixed
2016-02-17 09:05	Brad King	Fixed in Version	=> CMake 3.6
2016-02-17 09:05	Brad King	Target Version	=> CMake 3.6
2016-02-19 09:45	Brad King	Note Edited: 0040496
2016-06-10 14:21	Kitware Robot	Note Added: 0041244
2016-06-10 14:21	Kitware Robot	Status	resolved => closed