CVE-2009-0847 asn1buf_imbed incorrect length validation

CVE-2009-0847 asn1buf_imbed incorrect length validation

asn1buf_imbed() can perform pointer arithmetic that causes the "bound"
pointer of the subbuffer to be less than the "next" pointer.  This can
lead to malloc() failure or crash.

In asn1buf_imbed(), check the length before doing arithmetic to set
subbuf->bound.  In asn1buf_remove_octetstring() and
asn1buf_remove_charstring(), check for invalid buffer pointers before
executing an unsigned length check against a (casted to size_t)
negative number.

ticket: 6444
tags: pullup
target_version: 1.7

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@22175 dc483132-0cff-0310-8789-dd5450dbe970