linux-kernel - Re: [musl] AT_MINSIGSTKSZ mismatched interpretation kernel vs libc

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Message-ID: <20240902125125.GS10433@brightrain.aerifal.cx>
Date: Mon, 2 Sep 2024 08:51:26 -0400
From: Rich Felker <dalias@...c.org>
To: Florian Weimer <fweimer@...hat.com>
Cc: "H.J. Lu" <hjl.tools@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-api@...r.kernel.org, libc-alpha@...rceware.org,
	musl@...ts.openwall.com
Subject: Re: [musl] AT_MINSIGSTKSZ mismatched interpretation kernel vs libc

On Mon, Sep 02, 2024 at 02:07:36PM +0200, Florian Weimer wrote:
> * Rich Felker:
> 
> > This is ambiguously worded (does "operating system" mean kernel?) and
> > does not agree with POSIX, which defines it as:
> >
> >     Minimum stack size for a signal handler.
> >
> > And otherwise just specifies that sigaltstack shall fail if given a
> > smaller size.
> >
> > The POSIX definition is also underspecified but it's clear that it
> > should be possible to execute at least a do-nothing signal handler
> > (like one which immediately returns and whose sole purpose is to
> > induce EINTR when intalled without SA_RESTART), or even a minimal one
> > that does something like storing to a global variable, with such a
> > small stack. Allowing a size where even a do-nothing signal handler
> > results in a memory-clobbering overflow or access fault seems
> > non-conforming to me.
> 
> POSIX does not specify what happens on a stack overflow (or more
> generally, if most resource limits are exceeded), so I think the
> behavior is conforming on a technicality.

It doesn't specify what happens on overflow. It does specify what
happens on non-overflow: the program executes correctly. Failure to do
that is the problem here, not failure to trap on fault.

Rich