Rewrite BN_bn2dec.

This is a more complete fix for CVE-2016-2182. The original commit
message was:
"If an oversize BIGNUM is presented to BN_bn2dec() it can cause
BN_div_word() to fail and not reduce the value of 't' resulting
in OOB writes to the bn_data buffer and eventually crashing.

Fix by checking return value of BN_div_word() and checking writes
don't overflow buffer.

Thanks to Shi Lei for reporting this bug."

BoringSSL's rewrite commit message:
"958aaf1ea1b481e8ef32970d5b0add80504be4b2, imported from upstream, had
an off-by-one error. Reproducing the failure is fairly easy as it can't
even serialize 1. See also upstream's

Rewrite the function completely with CBB and add a basic test.


Change-Id: I41a91514c4bb9e83854824ed5258ffe4e49d9491
Bug: 32096880
(cherry picked from commit 29b92ab938c1a17d4d1b3b039042a0f499f58b5d)
2 files changed