If using SSecurityPlain and the user specifies an empty username
and password, it will invoke InStream::checkNoWait(0) which will
cause a division by zero when calculating the number of available
items.
Enhance InStream::check() to behave properly when asked for
zero items, or zero sized items.
Add comments to InStream::check(), InStream::checkNoWait(),
and InStream::readBytes() to document expected behaviour
when requested to check or read zero items, or an item with
zero size.
We use a lot of lengths given to us over the network, so be more
paranoid about them causing an overflow as otherwise an attacker
might trick us in to overwriting other memory.
This primarily affects the client which often gets lengths from the
server, but there are also some scenarios where the server might
theoretically be vulnerable.
Issue found by Pavel Cheremushkin from Kaspersky Lab.
Provides safety against them accidentally becoming negative because
of bugs in the calculations.
Also does the same to CharArray and friends as they were strongly
connection to the stream objects.
