Overflowing a signed integer in C is an undefined behaviour.
It is possible to trigger this undefined behaviour in tor_asprintf on
Windows or systems lacking vasprintf.
On these systems, eiter _vscprintf or vsnprintf is called to retrieve
the required amount of bytes to hold the string. These functions can
return INT_MAX. The easiest way to recreate this is the use of a
specially crafted configuration file, e.g. containing the line:
FirewallPorts AAAAA<in total 2147483610 As>
This line triggers the needed tor_asprintf call which eventually
leads to an INT_MAX return value from _vscprintf or vsnprintf.
The needed byte for \0 is added to the result, triggering the
overflow and therefore the undefined behaviour.
Casting the value to size_t before addition fixes the behaviour.
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Tobias Stoeckmann
0d4a689d3a