Bug#815548: suspicious code in entropy.cpp

[Harald Dunkel]

Package: xca
Version: 1.3.2-1

Hi folks,

I always wondered why xca can generate keys so fast.
Reading the code I stumbled over this in entropy.cpp:

        :
        random_from_file("/dev/random", 64);
        random_from_file("/dev/hwrng", 64);
        :

int Entropy::random_from_file(QString fname, unsigned amount, int weakness)
{
        char buf[256];
        const char *file;
        int fd, sum;
        QByteArray ba;

        ba = filename2bytearray(fname);
        file = ba.constData();

        fd = open(file, O_RDONLY | O_NONBLOCK);

        if (fd == -1)
                return 0;

        for (sum=0; amount > 0;) {
                int len = read(fd, buf, amount > sizeof buf ?
                                        sizeof buf : amount);
                if (len > 0) {
                        RAND_seed(buf, len);
                        seed_strength += len / weakness;
                        amount -= len;
                        sum += len;
                }
                if (len == -1) {
                        if (errno != EWOULDBLOCK)
                                qWarning("Error '%s' while reading '%s'\n",
                                        strerror(errno), file);
                        len = 0;
                }
                if (len == 0)
                        break;
        }
        close(fd);
#ifdef DEBUG_ENTROPY
        fprintf(stderr, "Entropy from file '%s' = %d bytes\n", file, sum);
#endif
        return sum;
}


Esp. the "if (len == 0) break;" together with the O_NONBLOCK looks
weird (IMHO). Doesn't this mean that if there is no entropy in
/dev/random at all, then it returns immediately instead of collecting
at least a few bits of random data?


Regards
Harri