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SubjectRe: [PATCH] dup2: Fix return value with oldfd == newfd and invalid fd
On Mon, May 11, 2009 at 12:26:59PM -0700, Linus Torvalds wrote:

> Hmm. They've been "unsigned int" for as long as our history goes back
> (including BK), but yes, making them "int" would have hidden this issue as
> well.
>
> That said, I think we had reasons to do our fd's as unsigned, ie the whole
> "compare against MAX" thing that doesn't take negative values into
> account.
>
> In fact, I think we should do more of those. Right now we literally depend
> on things like "max_fds" being "unsigned int", and that the compiler then
> turns all the
>
> if (fd < fdt->max_fds)
>
> tests silently into unsigned tests even when 'fd' is 'int'.
>
> So I suspect we should probably make fs/file.c use _more_ "unsigned int"
> rather than having less of them.

What we should do is a careful review of the propagation paths of file
descriptors ;-/ As it is, we have an interesting mix of int/unsigned/long
used to carry those around, and quite a few of those are used for -E...
as well. Note, BTW, that for userland code this bug mostly isn't - libc will
convert that value to int before returning to caller, so sign expansion or
not, we won't notice. The things like strace will, though...


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