david 7f2e704795 Reduce the maximum number of sockets from max_sd() - 4 to max_sd() - 5. I've ...

foudn that five files can be open on Mac OS X: stdin, stdout, stderr, /dev/tty,
and /private/var/run/utmpx. This could cause a non-root scan at a high scan
rateto fail with the message "Too many open files". I was able to cause this
with "nmap --min-rate 5000 localhost -p-".

That command still fails with the same error message, but for an entirely
different reason. After a while, one of the connect calls fails with an errno of
22 = EINVAL, Invalid argument. Whatever this means, the socket doesn't get
closed, Nmap just reports a "Strange error from connect". The socket is still
open but Nmap doesn't include it in its count of open sockets, so it's off by
one (or more, conceivably). This allows it to try to open one too many sockets
and bomb with an error message.

Note that running as non-root is important both because it uses a connect scan
and because non-root users have a lower limit on open files.

I've tried just closing the socket when EINVAL is returned, and that fixes the
problem. But that's likely to differ on different systems. Plus I don't know why
EINVAL is returned; maybe it's an OS bug. This only affects localhost scans and
only at high scan rates, so I'm leaving it alone.

2008-04-10 01:51:05 +00:00

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