Re: [RFC PATCH v2 4/7] csu: Fix standard fds' mode

[Adhemerval Zanella Netto]

On 19/04/23 18:16, Sergey Bugaev wrote:
> On Wed, Apr 19, 2023 at 11:45 PM Adhemerval Zanella Netto
>>>> is this really needed now? playing silly games with this fds will always 
>>>> result in silly prices.
>>
>> My understanding of this code is to enforce that on setuid program with
>> stdin/stdout/stderr closed any operation fail.
> 
> Yes, but is that still considered desirable / a good idea? As opposed
> to making such operations no-op successfully (opening /dev/null with
> the expected mode).
> 

Good question, this is essentially a hardening for setsuid binaries since
opening the file in the *expected* way is not the intended behavior (even
though the C runtime expects that STDIN_FILENO, STDOUT_FILENO, and
STDERR_FILENO are in fact opened). As far I could check, this is really a 
glibc extension (both FreeBSD and OpenBSD does not seem to add such 
hardening).

I am not really sure how effective is this hardening, it seems more a
development one to enforce that system daemon are spawned correctly.