[openssl-dev] [openssl.org #4545] Crash in crypto/rand/md_rand.c

[Mick Saxton via RT]

Hi

Before going any further I would like to state that I have only seen this problem when we have 10000 or more concurrent connections.

Mostly we notice it on Windows but I have seen it on linux (Ubuntu).

I first noticed it when using v1.0.2d but have seen it again since upgrading to v1.0.2h.

It can happen in one of two places and results in a call to MD_Update with a negative value.

I have come up with a temporary fix which avoids the possibility of crashing at the expense of some randomness.
The system is very highly stressed at this point so debugging further is difficult.

The fix I am using is probably not what you eventually will want to implement but it does improve stability.

273:            MD_Update(&m, &(state[st_idx]), (j - k) );
Change to
273:            MD_Update(&m, &(state[st_idx]), (j - k) > 0 ? j - k : 1);  // micks at 1e.com (j -k) must not be negative

And

495:            MD_Update(&m, &(state[st_idx]), MD_DIGEST_LENGTH / 2 - k )
Change to
495:            MD_Update(&m, &(state[st_idx]), MD_DIGEST_LENGTH / 2 - k > 0 ? MD_DIGEST_LENGTH / 2 - k : 1);  // micks at 1e.com (j -k) must not be negative


I do have a test program which can reproduce this behaviour.

If I can be of further help - please contact me by email.

Regards
Mick Saxton

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