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Date: Tue, 22 Mar 2011 19:01:09 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: O_ACCMODE is wrong
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On Mar 22 11:40, Eric Blake wrote:
> First, some background: POSIX 2008 introduced O_SEARCH and O_EXEC, and
> states that they may (but not must) share the same bit, since the former
> is for directories and the latter for non-directories (cygwin shares
> these as 0x400000).  POSIX states that implementations need not reject
> O_EXEC|O_RDONLY (to cater to systems like cygwin where O_RDONLY is 0),
> but that they may on systems where it is detectable (such as on Hurd
> where O_RDONLY is 1).  It also requires that an application must provide
> exactly one of the five modes O_RDONLY, O_WRONLY, O_RDWR, O_SEARCH, or
> O_EXEC), and therefore an implementation should reject a bit-wise or
> that tries to mix those modes).
> 
> However, in introducing the new values, POSIX also required that
> O_ACCMODE be updated to cover those new modes.
> 
> Now for the bugs: cygwin's <fcntl.h> defines O_ACCMODE as 3 instead of
> 0x400003, and as a result, a regular file opened for O_EXEC (or a
> directory for O_SEARCH) but probed via fcntl(F_GETFL)&O_ACCMODE will
> mistakenly show up as O_RDONLY instead of the proper mode.  Meanwhile,
> open(O_EXEC|O_WRONLY) isn't rejected as an invalid mode.  However, just
> changing O_ACCMODE to the correct value may expose other latent bugs in
> the rest of cygwin1.dll, since it looks like there are existing places
> where cygwin is making assumptions that rely on O_ACCMODE being exactly
> 3, so it would require a careful audit to fix it all.

Given that O_EXEC and O_SEARCH are not used anywhere in Cygwin it's not
exactly a pressing issue.  If you want to add the correct handling, feel
free to send a patch.


Corinna


P.S.: In theory this is better suited for the cygwin-developers list...


-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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