Re: CVS commit: src/bin/sh

[christos%astron.com@localhost (Christos Zoulas)]

In article <20141018221947.GA2800%apb-laptoy.apb.alt.za@localhost>,
Alan Barrett  <apb%cequrux.com@localhost> wrote:
>On Wed, 15 Oct 2014, Christos Zoulas wrote:
>>Modified Files:
>>	src/bin/sh: redir.c
>>
>>Log Message:
>>PR/48201: Miwa Susumu: Fix set -C (no clobber) for POSIX; from FreeBSD
>>Can't use O_EXCL because of device nodes; also truncate.
>
>There are some TOCTOU races in this code, where something about 
>the file could change in between the stat() and the open().
>
>Some ideas:
>
>1. Keep the new code, with its races, but also verify that st_dev 
>and st_ino values remain unchanged between the stat() before 
>opening the file, and fstat() after opening the file.
>
>2. Try open() with O_EXCL first, and fall back to racy code with 
>stat() only if the first open(O_EXCL) fails.  Also use fstat() to 
>check that st_dev/st_ino do not change.
>
>3. Invent one or more open(2) flags, such as O_SPECIAL for "must 
>be a device or other special file, must not be a plain file or a 
>directory".  First try open(O_EXCL), and if that fails then try 
>open(O_SPECIAL).

Well, we could try to open without O_CREAT first, for device nodes
it should succeed, if it fails do the O_EXCL thingy. I think open has
enough flags.

christos