Changeset 5eab298f for lib

Timestamp:

2015-01-26T03:27:24Z (10 years ago)

Author:

dequis <dx@…>

Branches:

master

Children:

73ee390

Parents:

11e7828

git-author:

dequis <dx@…> (10-07-14 11:07:51)

git-committer:

dequis <dx@…> (26-01-15 03:27:24)

Message:

random_bytes: Use /dev/urandom only, don't bother trying /dev/random

Also abort() if there's no /dev/urandom

See ​http://www.2uo.de/myths-about-urandom/ for details.

File:

• lib/misc.c (modified) (1 diff)

lib/misc.c

@@ -414 +414 @@
 }
 
-/* A pretty reliable random number generator. Tries to use the /dev/random
-   devices first, and falls back to the random number generator from libc
-   when it fails. Opens randomizer devices with O_NONBLOCK to make sure a
-   lack of entropy won't halt BitlBee. */
+/* A wrapper for /dev/urandom.
+ * If /dev/urandom is not present or not usable, it calls abort()
+ * to prevent bitlbee from working without a decent entropy source */
 void random_bytes( unsigned char *buf, int count )
 {
-        static int use_dev = -1;
-        
-        /* Actually this probing code isn't really necessary, is it? */
-        if( use_dev == -1 )
-        {
-                if( access( "/dev/random", R_OK ) == 0 || access( "/dev/urandom", R_OK ) == 0 )
-                        use_dev = 1;
-                else
-                {
-                        use_dev = 0;
-                        srand( ( getpid() << 16 ) ^ time( NULL ) );
-                }
-        }
-        
-        if( use_dev )
-        {
-                int fd;
-                
-                /* At least on Linux, /dev/random can block if there's not
-                   enough entropy. We really don't want that, so if it can't
-                   give anything, use /dev/urandom instead. */
-                if( ( fd = open( "/dev/random", O_RDONLY | O_NONBLOCK ) ) >= 0 )
-                        if( read( fd, buf, count ) == count )
-                        {
-                                close( fd );
-                                return;
-                        }
-                close( fd );
-                
-                /* urandom isn't supposed to block at all, but just to be
-                   sure. If it blocks, we'll disable use_dev and use the libc
-                   randomizer instead. */
-                if( ( fd = open( "/dev/urandom", O_RDONLY | O_NONBLOCK ) ) >= 0 )
-                        if( read( fd, buf, count ) == count )
-                        {
-                                close( fd );
-                                return;
-                        }
-                close( fd );
-                
-                /* If /dev/random blocks once, we'll still try to use it
-                   again next time. If /dev/urandom also fails for some
-                   reason, stick with libc during this session. */
-                
-                use_dev = 0;
-                srand( ( getpid() << 16 ) ^ time( NULL ) );
-        }
-        
-        if( !use_dev )
-        {
-                int i;
-                
-                /* Possibly the LSB of rand() isn't very random on some
-                   platforms. Seems okay on at least Linux and OSX though. */
-                for( i = 0; i < count; i ++ )
-                        buf[i] = rand() & 0xff;
-        }
+        int fd;
+        if( ( ( fd = open( "/dev/urandom", O_RDONLY ) ) == -1 ) ||
+            ( read( fd, buf, count ) == -1 ) )
+        {
+                log_message( LOGLVL_ERROR, "/dev/urandom not present - aborting" );
+                abort();
+        }
+
+        close( fd );
 }