[openssl-users] In ssl3_write_bytes, some checks related to hanlding write failure are missing

Raja ashok raja.ashok at huawei.com
Mon Mar 27 08:25:16 UTC 2017


I feel there is a check missing in ssl3_write_bytes, in case of handling write failure.

Consider SSL_write is called with 20000 bytes buffer, then internally in ssl3_write_bytes we try to send it as two record (16384 and 3616). If TCP send failed for the second record then we store the states internally (wnum, wpend_tot and wpend_buf) and return back the result.

Later application has to call SSL_write with same buffer, if it calls with different buffer of length 100 byte then we fail that in ssl3_write_bytes using the check (len < tot).

But consider application calls with buffer of size 18000 bytes and SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER is enabled. Then (len < tot) will not succeed as tot is 16384. Then it will call ssl3_write_pending to send the remaining 3616 record. If it succeeds we are incrementing tot, (tot += i). Now tot will have 20000.

Later there is a check (tot == len), this will not succeed. Then directly we are doing n = (len - tot), this will overflow and store a value close to 2^32 in n. Then it will cause out of bound access to the application buffer "buf".

I hope we should have one more check (len < (tot + s->s3->wpend_tot)) before calling ssl3_write_pending.

    if ((len < tot) || (len < (tot + s->s3->wpend_tot))){
        return (-1);

Note : I am referring 1.0.2k version of OpenSSL.



Raja Ashok V K
Huawei Technologies
Bangalore, India
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