midb_agent: reduce stack usage / resolve OOB write

4. tainted_data_return: Called function read(pback->sockd, buff +
offset, 262144 - offset), and a possible return value may be less
than zero.
5. cast_overflow: An assign that casts to a different type, which
might trigger an overflow.
CID 1589501: (#1 of 1): Overflowed array index write (INTEGER_OVERFLOW) [enum_subscriptions]
CID 1589502: (#1 of 1): Overflowed array index write (INTEGER_OVERFLOW) [enum_folders]
CID 1589506: (#1 of 1): Overflowed array index write (INTEGER_OVERFLOW) [fetch_detail_uid]
CID 1589510: (#1 of 1): Overflowed array index write (INTEGER_OVERFLOW) [list_deleted]
CID 1589520: (#1 of 1): Overflowed array index write (INTEGER_OVERFLOW) [fetch_simple_uid]
CID 1589522: (#1 of 1): Overflowed array index write (INTEGER_OVERFLOW) [list_mail]
8. deref_overflow: offset, which might have overflowed, is used in a
pointer index in buff[offset].

Basically, if ``read()`` fills the complete buffer (256K), then
buff[offset]='\0' will write to one past the last. Switching to
std::string helps get rid of the huge stack variable as well as
getting a safe guaranteed terminator.

Author: jengelh

Makefile.am

@@ -126,7 +126,7 @@ libgxs_event_stub_la_LIBADD = -lpthread ${libHX_LIBS} libgromox_common.la
 EXTRA_libgxs_event_stub_la_DEPENDENCIES = default.sym
 libgxs_midb_agent_la_SOURCES = mra/midb_agent.cpp mra/midb_agent.hpp
 libgxs_midb_agent_la_LDFLAGS = ${default_SYFLAGS}
-libgxs_midb_agent_la_LIBADD = -lpthread ${libHX_LIBS} libgromox_common.la
+libgxs_midb_agent_la_LIBADD = -lpthread ${fmt_LIBS} ${libHX_LIBS} libgromox_common.la
 EXTRA_libgxs_midb_agent_la_DEPENDENCIES = default.sym
 
 http_SOURCES = exch/http/cache.cpp exch/http/cache.hpp exch/http/fastcgi.cpp exch/http/fastcgi.hpp exch/http/hpm_processor.cpp exch/http/hpm_processor.hpp exch/http/http_parser.cpp exch/http/http_parser.hpp exch/http/listener.cpp exch/http/listener.hpp exch/http/main.cpp exch/http/pdu_ndr.cpp exch/http/pdu_ndr.hpp exch/http/pdu_ndr_ids.hpp exch/http/pdu_processor.cpp exch/http/pdu_processor.hpp exch/http/resource.hpp exch/http/rewrite.cpp exch/http/rewrite.hpp exch/http/system_services.cpp exch/http/system_services.hpp