Re: [PATCH 1/5] __fdelt_chk: Removed range check

[KOSAKI Motohiro <kosaki dot motohiro at gmail dot com>]

> Is there a simple way to check which software will crash with this
> change?  That way we can assess what is the probability thing will
> crash?  Perhaps that will give us an idea what the probability third
> party software will be affected?

The difficulty depend on that you can allow overlooking or not. IOW, there is
no simple and exact checking way.

Technically, the condition is,

- Uses much FDs larger than FD_SETSIZE.
- Allocate fd_set as dynamic array (by malloc, calloc or something).
- Uses FD_SET, FD_CLR, or FD_ISSET.

The difficulty is, both malloc and FD_SET is too frequently used and
grep unfriendly.

You can also use the following heuristics. but please keep mind they
may have false positive/negative.

- Sometimes, A software which uses the Linux extension uses howmany()
  macro. but there are several exceptions. at least, glibc manual allow not
  to use howmany.
- Sometimes, A software which uses the Linux extension doesn't use
  FD_ZERO because calloc() initialized file descriptor bitmaps and
  FD_ZERO is not necessary. But there are exceptions too. Several
  softwares prefer to initialize explicitly by FD_ZERO.

So, you need manual inspection anyway. Please let me know if you have
an alternative good idea to asses this.