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Message-ID: <20250217143829.GA1827@brightrain.aerifal.cx>
Date: Mon, 17 Feb 2025 09:44:58 -0500
From: Rich Felker <dalias@...c.org>
To: Alejandro Colomar <alx@...nel.org>
Cc: libc-help@...rceware.org, linux-man@...r.kernel.org,
Karlson2k <k2k@...od.ru>, Tobias Stoeckmann <tobias@...eckmann.org>,
Serge Hallyn <serge@...lyn.com>, Iker Pedrosa <ipedrosa@...hat.com>,
musl@...ts.openwall.com
Subject: Re: Re: [shadow-maint/shadow] Add cheap defense mechanisms
(PR #1171)
On Mon, Feb 17, 2025 at 10:42:06AM +0100, Alejandro Colomar wrote:
> Hi,
>
> On Sun, Feb 16, 2025 at 06:15:18PM -0800, Karlson2k wrote:
> > Karlson2k left a comment (shadow-maint/shadow#1171)
> >
> > Doesn't use of glibc extensions break functioning with non-glibc, like musl?
>
> Hmmm, I didn't know musl doesn't support this. It would be interesting
> to get them to support it. I've CCd several interested parties in this
> email.
It's in the latest POSIX and we have supported it for a long time as
POSIX-future (since 2012/release 0.9.7).
> > Isn't it safe to use constructs like
> > ``` C
> > shadow = fopen (SGROUP_FILE, "re");
> > if (NULL == shadow )
> > shadow = fopen (SGROUP_FILE, "r");
> > ```
> > ?
Unfortunately this doesn't work because it's UB to pass any modes but
the standards-specified ones.
In any case use of fopen is just gratuitously bad for software that
targets POSIX. The right way to do things is a two-step open+fdopen.
This avoids needing to depend on new features to open and lets you use
all the modern open flags, openat if needed, etc.
Rich
P.S. Had to omit shadow-utils <~hallyn/shadow@...ts.sr.ht> from CC
because my mail software rejects / in an address... gotta fix that.
Apologies.
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