Bugtraq: Re: SECURITY.NNOV: Multiple applications fd_set structure bitmap array index overflow

[Casper.Dik () Sun COM]

> from linux/posix_types/h:
> #undef      __FD_SETSIZE
> #define     __FD_SETSIZE   1024
>
> Well, you *can* change it, but it requires a recompile of the kernel and 
> all userland programs that create an fd_set.
Which is generally true for most Unix systems; traditionallly you can
redefine FD_SETSIZE for a larger set but you're limited by kernel
support (or libc support, as the case may be)

> In this regard, windows did get it right. However, the earlier comment 
> on using the windows async sockets is spot on, if you want performance. 
> Windows fd_set's are structured more like unix poll() arrays (un-ordered 
> array of fd's) and are not very efficient if there are many sockets on 
> one set. Also, a linux fd_set limits the fd *value* to < 1024, not just 
> the number of fd's in the set. So it's possible to only want to put one 
> fd on a fd_set but be unable to do so if it's value is > FD_SETSIZE 
> (which can be done by increasing the maximum number of file handles a 
> process is permitted to open).
Which is why poll(2) is the superior interface; but event driven
machnisms are in the end the best.

Casper