Re: predictable IP ID

Theodore Y. Ts'o (tytso@mit.edu)
Mon, 4 Oct 1999 14:46:34 -0400

Um, if the "predictable IP ID's" under discussion is the "TESO SEcurity
Advisonary" talking about the Linux Kernel 2.2.x ISN Vulernerability,
this is fixed already in the latest pre-2.2 kernel issued by Alan (I
believe; Alan, you did get this both into the ac kernels and the pre-2.2
kernel seriesl, right?) The problem is that the secret used in
secure_tcp_sequence_number isn't getting initialized correctly, due to a
type problem in get_random_bytes(). We should try the simple fix before
we start talking about extreme measures such as installing AVL trees. :-)

To the Teso crew, if you could try redoing your analysis with the
following patch applied, I would greatly appreciate it. The problem is
that the secret[] isn't array isn't getting properly initialized, and
the crypto hash doesn't work well when the secret is all zero's. Chalk
this up to another example of "why C is inherently an unsafe programming
langauge". (blush)

if (!rekey_time || (tv.tv_sec - rekey_time) > REKEY_INTERVAL) {
rekey_time = tv.tv_sec;
/* First three words are overwritten below. */
- get_random_bytes(&secret+3, sizeof(secret)-12);
+ get_random_bytes(&secret[3], sizeof(secret)-12);
count = (tv.tv_sec/REKEY_INTERVAL) << HASH_BITS;
}

- Ted

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