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Date: Sat, 23 Feb 2013 00:01:39 -0500
From: KOSAKI Motohiro <kosaki.motohiro@...il.com>
To: Rich Felker <dalias@...ifal.cx>
Cc: libc-alpha <libc-alpha@...rceware.org>, musl@...ts.openwall.com
Subject: Re: O_EXEC and O_SEARCH
> 1. Try to open with O_RDONLY. If it succeeds, we're done. This is
> REALLY nice because it means O_SEARCH and O_EXEC "just work" even on
> ancient or broken kernels as long as the target file is readable.
Hmm..
This algorithm seems slightly strange to me. Why do you want to try O_RDONLY at
first?
O_RDONLY require read permission and O_SEARCH, if i understand correctly,
doesn't.
I think you should try O_PATH at first.
>
> 2. Else, add O_PATH and try again. If it still fails, we have a
> pre-2.6.39 kernel and there's nothing we can do, so just report
> failure.
>
> 3. If open succeeds with O_PATH, then if O_NOFOLLOW is also specified,
> check fstat, and close the file and report error if fstat succeeded
> and the obtained fd was a symbolic link.
>
> 4. If fstat failed, we have a buggy kernel, so either close and report
> an error, or just ignore the failure (possibly ignoring the
> requirements of O_NOFOLLOW), as there seems to be no way to handle it
> correctly on such kernels.
>
> If the kernel developers ever add O_SEARCH/O_EXEC at the kernel level
> with our proposed value of 3, a step 0, just passing the value to the
> kernel directly and seeing if it works, could also be added.
>
> Rich
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