From owner-cvs-all  Tue Feb 27  0:33:59 2001
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Date: Tue, 27 Feb 2001 19:33:44 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Jonathan Lemon <jlemon@FreeBSD.org>
Cc: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sys/kern sys_generic.c
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On Mon, 26 Feb 2001, Jonathan Lemon wrote:

> jlemon      2001/02/26 16:50:20 PST
> 
>   Modified files:
>     sys/kern             sys_generic.c 
>   Log:
>   Cast nfds to u_int before range checking it in order to catch negative
>   values.
>   
>   PR:	25393

Wrong fix:

1. The cast may be unportable.  It's not clear that it works for 1's
   complement, etc.
2. This hack shouldn't be used in new code.  Just compare with 0 explicitly.
   If the cast would work, then the compiler should be capable optimizing
   away the comparison if that would be an optimization.  gcc has done this
   for 10-15 years, at least on i386's.
3. poll() has passed an unsigned count, but the count has been corrupted
   by assigning it to an int.  The correctness of all this depends on
   the cast to u_int converting back to the original value.  Do you
   really want to know if all this works for 1's complement, etc? :-)
   The patch in the PR does this right (use the correct type for nfds so
   that things just work.

This was broken in peter's recent changes (RELENG_4 still does the bounds
check directly on the u_int in the struct.  When I reviewed the changes,
I stared a bit at the u_int in the struct, but I missed the use of the
wrong type for the local vatriable :(.

Bruce


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