Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <5e3946e1-f4bb-e3f8-11e9-be26589972b6@gmail.com>
Date:   Wed, 6 Apr 2022 21:31:57 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.7.0
Subject: Re: [Bug 215813] syscall(SYS_vfork) causes execve() to return 0.
 (was: vfork(2) behavior not consistent with fork(2))
Content-Language: en-US
To:     Florian Weimer <fweimer@redhat.com>
Cc:     Christian Brauner <brauner@kernel.org>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        linux-kernel@vger.kernel.org,
        =?UTF-8?B?0JrQvtGA0LXQvdCx0LXRgNCzINCc0LDRgNC6?= 
        <socketpair@gmail.com>, Andrei Vagin <avagin@openvz.org>,
        Dmitry Safonov <dima@arista.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Arnd Bergmann <arnd@arndb.de>, Serge Hallyn <serge@hallyn.com>,
        linux-api@vger.kernel.org, bugzilla-daemon@kernel.org
References: <bug-215769-216477@https.bugzilla.kernel.org/>
 <bug-215769-216477-to2O9X1Knw@https.bugzilla.kernel.org/>
 <4fb02f5f-60f9-42af-ddd5-fe5af877231f@gmail.com>
 <20220404080519.pi6izyuop3mmdg2g@wittgenstein>
 <ae2cbf67-aace-bc40-418e-7b41873f814a@gmail.com>
 <20220406084613.3srklyt27qxcmrcx@wittgenstein>
 <f21a06dc-1e2a-87cd-59dc-e8d5245b0a50@gmail.com>
 <87k0c2qagv.fsf@oldenburg.str.redhat.com>
From:   Alejandro Colomar <alx.manpages@gmail.com>
In-Reply-To: <87k0c2qagv.fsf@oldenburg.str.redhat.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi Florian,

On 4/6/22 21:26, Florian Weimer wrote:
> It's not clear if this is valid.  The syscall function in glibc does not
> protect the on-stack return address against overwriting, so it can't be
> used to call SYS_vfork on x86.
> 
> Can you reproduce this with a true inline syscall, or the glibc vfork
> function (which protects the return address)?

If you tell me how I can call a syscall without the libc wrapper or 
syscall(2), sure, I can try :)

If syscall(2) can't be used for certain syscalls, maybe we should 
document that.

Thanks,

Alex