Do not seed /dev/urandom. urandom is non-writeable on some devices. Because only OpenSSL seeding is broken, this should not result in security problems!

This commit is contained in:
Dominik Schürmann 2013-09-15 22:27:09 +02:00
parent c90e776055
commit e05d17eec2

View File

@ -18,9 +18,7 @@ import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.security.NoSuchAlgorithmException;
import java.security.Provider;
@ -35,6 +33,19 @@ import java.security.Security;
* Architecture primitives. A good place to invoke them is in the application's {@code onCreate}.
*
* copied from http://android-developers.blogspot.de/2013/08/some-securerandom-thoughts.html
*
*
* Sep 15, 2013:
* On some devices /dev/urandom is non-writable!
* No need to seed /dev/urandom. urandom should have enough seeds from the OS and kernel.
* Only OpenSSL seeds are broken. See http://emboss.github.io/blog/2013/08/21/openssl-prng-is-not-really-fork-safe
*
* see also:
* https://github.com/k9mail/k-9/commit/dda8f64276d4d29c43f86237cd77819c28f22f21
* In addition to a couple of custom ROMs linking /dev/urandom to a non-writable
* random version, now Samsung's SELinux policy also prevents apps from opening
* /dev/urandom for writing. Since we shouldn't need to write to /dev/urandom anyway
* we now simply don't.
*/
public final class PRNGFixes {
@ -138,6 +149,7 @@ public final class PRNGFixes {
* {@code Provider} of {@code SecureRandom} engines which pass through all requests to the Linux
* PRNG.
*/
@SuppressWarnings("serial")
private static class LinuxPRNGSecureRandomProvider extends Provider {
public LinuxPRNGSecureRandomProvider() {
@ -155,6 +167,7 @@ public final class PRNGFixes {
/**
* {@link SecureRandomSpi} which passes all requests to the Linux PRNG ({@code /dev/urandom}).
*/
@SuppressWarnings("serial")
public static class LinuxPRNGSecureRandom extends SecureRandomSpi {
/*
@ -178,40 +191,40 @@ public final class PRNGFixes {
*/
private static DataInputStream sUrandomIn;
/**
* Output stream for writing to Linux PRNG or {@code null} if not yet opened.
*
* @GuardedBy("sLock")
*/
private static OutputStream sUrandomOut;
/**
* Whether this engine instance has been seeded. This is needed because each instance needs
* to seed itself if the client does not explicitly seed it.
*/
private boolean mSeeded;
// /**
// * Output stream for writing to Linux PRNG or {@code null} if not yet opened.
// *
// * @GuardedBy("sLock")
// */
// private static OutputStream sUrandomOut;
//
// /**
// * Whether this engine instance has been seeded. This is needed because each instance needs
// * to seed itself if the client does not explicitly seed it.
// */
// private boolean mSeeded;
@Override
protected void engineSetSeed(byte[] bytes) {
try {
OutputStream out;
synchronized (sLock) {
out = getUrandomOutputStream();
}
out.write(bytes);
out.flush();
mSeeded = true;
} catch (IOException e) {
throw new SecurityException("Failed to mix seed into " + URANDOM_FILE, e);
}
// try {
// OutputStream out;
// synchronized (sLock) {
// out = getUrandomOutputStream();
// }
// out.write(bytes);
// out.flush();
// mSeeded = true;
// } catch (IOException e) {
// throw new SecurityException("Failed to mix seed into " + URANDOM_FILE, e);
// }
}
@Override
protected void engineNextBytes(byte[] bytes) {
if (!mSeeded) {
// Mix in the device- and invocation-specific seed.
engineSetSeed(generateSeed());
}
// if (!mSeeded) {
// // Mix in the device- and invocation-specific seed.
// engineSetSeed(generateSeed());
// }
try {
DataInputStream in;
@ -251,19 +264,19 @@ public final class PRNGFixes {
}
}
private OutputStream getUrandomOutputStream() {
synchronized (sLock) {
if (sUrandomOut == null) {
try {
sUrandomOut = new FileOutputStream(URANDOM_FILE);
} catch (IOException e) {
throw new SecurityException("Failed to open " + URANDOM_FILE
+ " for writing", e);
}
}
return sUrandomOut;
}
}
// private OutputStream getUrandomOutputStream() {
// synchronized (sLock) {
// if (sUrandomOut == null) {
// try {
// sUrandomOut = new FileOutputStream(URANDOM_FILE);
// } catch (IOException e) {
// throw new SecurityException("Failed to open " + URANDOM_FILE
// + " for writing", e);
// }
// }
// return sUrandomOut;
// }
// }
}
/**