Nico, good day.
Thu, May 21, 2009 at 11:00:23AM +0200, Nico Golde wrote:
> * Eygene Ryabinkin <r...@codelabs.ru> [2009-05-21 10:24]:
> > Thu, May 21, 2009 at 09:50:12AM +0400, Eygene Ryabinkin wrote:
> > > Wed, May 20, 2009 at 05:39:08PM +0200, Mike Massonnet wrote:
> > > > Wow, nice! I didn't take time yet to investigate, thanks for a lot for
> > > > providing this patch. I will make a package for stable asap.
> > >
> > > Erm, sorry, sent old patch variant that doesn't produce .Xauthority:
> > > 'quit' should be replaced with 'exit'. Sorry, wasn't updated the
> > > patchfile. Here is the proper one:
> >
> > And found one more issue -- mcookie was weakened because I am blindly
> > substituted 'int r' for 'bool r'. Fixed now.
>
> Thanks very much, the patch looks good! While you're at it, mind to
> fix the insecure "random" hexstring generation as well?
Sure, did it already, tested and just wanted to send it out.
From 5beb217296e3074cadc5bcb3e40355f54ee705f0 Mon Sep 17 00:00:00 2001
From: Eygene Ryabinkin <r...@shadow.codelabs.ru>
Date: Thu, 21 May 2009 11:56:27 +0400
Subject: [PATCH] Create interface for random number generator and use it
everywhere
Don't use rand()/srand() at all -- they are very weak. Provide our
wrappers for random()/srandom() and make utility function that will
generate seed for srandom.
Rework MIT magic cookie generation: consume 4 bytes of input in one
pass -- random() should produce values that are usable for this purpose.
Signed-off-by: Eygene Ryabinkin <r...@shadow.codelabs.ru>
---
app.cpp | 49 ++++++++++++++++++++++++++-----------------------
app.h | 2 ++
util.cpp | 37 +++++++++++++++++++++++++++++++++++++
util.h | 5 +++++
4 files changed, 70 insertions(+), 23 deletions(-)
diff --git a/app.cpp b/app.cpp
index 04caaa1..0ac8c3a 100644
--- a/app.cpp
+++ b/app.cpp
@@ -129,15 +129,18 @@ void User1Signal(int sig) {
#ifdef USE_PAM
-App::App(int argc, char** argv):
- pam(conv, static_cast<void*>(&LoginPanel)){
+App::App(int argc, char** argv)
+ : pam(conv, static_cast<void*>(&LoginPanel)),
#else
-App::App(int argc, char** argv){
+App::App(int argc, char** argv)
+ :
#endif
+ mcookiesize(32) // Must be divisible by 4
+{
int tmp;
ServerPID = -1;
testing = false;
- mcookie = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
+ mcookie = string(App::mcookiesize, 'a');
daemonmode = false;
force_nodaemon = false;
firstlogin = true;
@@ -1128,13 +1131,13 @@ string App::findValidRandomTheme(const string& set)
name = name.substr(0, name.length() - 1);
}
- srandom(getpid()+time(NULL));
+ Util::srandom(Util::makeseed());
vector<string> themes;
string themefile;
Cfg::split(themes, name, ',');
do {
- int sel = random() % themes.size();
+ int sel = Util::random() % themes.size();
name = Cfg::Trim(themes[sel]);
themefile = string(THEMESDIR) +"/" + name + THEMESFILE;
@@ -1161,27 +1164,27 @@ void App::replaceVariables(string& input,
}
+/*
+ * We rely on the fact that all bits generated by Util::random()
+ * are usable, so we are taking full words from its output.
+ */
void App::CreateServerAuth() {
/* create mit cookie */
- int i, r;
- int hexcount = 0;
- string authfile;
- string cmd;
+ uint16_t word;
+ uint8_t hi, lo;
+ int i;
+ string authfile;
const char *digits = "0123456789abcdef";
- srand( time(NULL) );
- for ( i = 0; i < 31; i++ ) {
- r = rand()%16;
- mcookie[i] = digits[r];
- if (r>9)
- hexcount++;
+ Util::srandom(Util::makeseed());
+ for (i = 0; i < App::mcookiesize; i+=4) {
+ word = Util::random() & 0xffff;
+ lo = word & 0xff;
+ hi = word >> 8;
+ mcookie[i] = digits[lo & 0x0f];
+ mcookie[i+1] = digits[lo >> 4];
+ mcookie[i+2] = digits[hi & 0x0f];
+ mcookie[i+3] = digits[hi >> 4];
}
- /* MIT-COOKIE: even occurrences of digits and hex digits */
- if ((hexcount%2) == 0) {
- r = rand()%10;
- } else {
- r = rand()%5+10;
- }
- mcookie[31] = digits[r];
/* reinitialize auth file */
authfile = cfg->getOption("authfile");
remove(authfile.c_str());
diff --git a/app.h b/app.h
index 7b4bd10..9a44269 100644
--- a/app.h
+++ b/app.h
@@ -101,6 +101,8 @@ private:
std::string themeName;
std::string mcookie;
+
+ const int mcookiesize;
};
diff --git a/util.cpp b/util.cpp
index 309ce4f..5ed972f 100644
--- a/util.cpp
+++ b/util.cpp
@@ -7,7 +7,13 @@
(at your option) any later version.
*/
+#include <sys/types.h>
+
#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <unistd.h>
+
#include "util.h"
/*
@@ -30,3 +36,34 @@ bool Util::add_mcookie(const std::string &mcookie, const
char *display,
pclose(fp);
return true;
}
+
+/*
+ * Interface for random number generator. Just now it uses ordinary
+ * random/srandom routines and serves as a wrapper for them.
+ */
+void Util::srandom(unsigned long seed)
+{
+ ::srandom(seed);
+}
+
+long Util::random(void)
+{
+ return ::random();
+}
+
+/*
+ * Makes seed for the srandom() using "random" values obtained from
+ * getpid(), time(NULL) and others.
+ */
+long Util::makeseed(void)
+{
+ struct timespec ts;
+ long pid = getpid();
+ long tm = time(NULL);
+
+ if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0) {
+ ts.tv_sec = ts.tv_nsec = 0;
+ }
+
+ return pid + tm + (ts.tv_sec ^ ts.tv_nsec);
+}
diff --git a/util.h b/util.h
index 8bd52be..b8d2993 100644
--- a/util.h
+++ b/util.h
@@ -14,6 +14,11 @@
namespace Util {
bool add_mcookie(const std::string &mcookie, const char *display,
const std::string &xauth_cmd, const std::string &authfile);
+
+ void srandom(unsigned long seed);
+ long random(void);
+
+ long makeseed(void);
};
#endif /* __UTIL_H__ */
--
1.6.3.1
--
rea
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