net-snmp SIGSEGV: not enough space or error in allocation for extenstion

[Graham Leggett]

When a certificate contains an extension that when printed becomes longer than 512 bytes (for example certificate transparency as used in modern certs) net-snmp crashes on startup with a SIGSEGV.

The following patches fix the problem by:

- Increasing the buffer size from 512 to 4096 bytes when dumping cert extensions.

- Checking for NULL before attempting a strchr, fixing the crash.

Bug report with fix at https://github.com/net-snmp/net-snmp/issues/233.

Individual patches:

https://github.com/net-snmp/net-snmp/commit/9d001c34196df47526260441af35a509a325e41f.diff
https://github.com/net-snmp/net-snmp/commit/4c5d2ceae4d4a8b77db48fc8fff77e14943ff4d3.diff
https://github.com/net-snmp/net-snmp/commit/bb30f8ee0075750fd3648a6bf3fab543f46152ed.diff
https://github.com/net-snmp/net-snmp/commit/969226ea501b92e1a2ed427bc1a46f18ef2890b7.diff

[Graham Leggett (minfrin-y)]

Same bug at RHEL: https://bugzilla.redhat.com/show_bug.cgi?id=1908718

[Graham Leggett (minfrin-y)]

This bug is a duplicate of: https://bugs.launchpad.net/ubuntu/+source/net-snmp/+bug/1912389