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Re: [PATCH 2/2] Ignore failure of setting mode on a temporary file on OS

From: Paul Eggert
Subject: Re: [PATCH 2/2] Ignore failure of setting mode on a temporary file on OS/2
Date: Tue, 17 Oct 2023 11:58:01 -0700
User-agent: Mozilla Thunderbird

On 10/17/23 11:16, Zack Weinberg wrote:
On Sun, Oct 15, 2023, at 3:43 AM, KO Myung-Hun wrote:
How about this ?
1. create and close a temporary file
2. chmod() on it
3. re-open it with O_TRUNC ?

The trouble is, on a multi-user system, any time you do any operation
by name on a file whose full pathname includes a world-writable
directory (such as the system-wide scratch directories), even if that
directory is “sticky” (chmod +t), you have to be exquisitely careful,
or a malicious concurrent process might be able to trick you into
overwriting some file elsewhere on the filesystem.  For example, your
steps 2 and 3, if executed as root on a file expected to exist in
/tmp, would give a malicious concurrent process a chance to clobber
the access control bits and/or the contents of *any file*, by moving
the temporary file out of the way

? If /tmp is sticky, a malicious process can't rename /tmp/foo.

The rest of your email and patch look good to me, though admittedly I haven't used perl for real in 30 years.

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