If a signature is longer than max allowed adb signature length
then adb_walk_block writes out of boundary of stack variable tmp.
The len += snprintf is not safe per standard snprintf implementation
(kernel does it differently). Introduce and use apk_blob_push_fmt
which does the checking better.
Fixes#10752
Reported-by: Samanta Navarro <ferivoz@riseup.net>
EVP_MD_CTX_set_pkey_ctx() is fairly new openssl function, and not
existing in many alternative. Use EVP_MD_CTX_reset() which is slightly
more heavy but more portable. Add also signature buffer lengths to
work with RSA.
Timo Teräs