From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37755) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZtHPF-00051T-4V for qemu-devel@nongnu.org; Mon, 02 Nov 2015 10:52:25 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZtHPB-0002iW-0q for qemu-devel@nongnu.org; Mon, 02 Nov 2015 10:52:25 -0500 References: <1446473439-10701-1-git-send-email-pbonzini@redhat.com> <56377EBC.5030402@redhat.com> From: Paolo Bonzini Message-ID: <563786B0.9060300@redhat.com> Date: Mon, 2 Nov 2015 16:52:16 +0100 MIME-Version: 1.0 In-Reply-To: <56377EBC.5030402@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] qemu-sockets: do not test path with access() before unlinking List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cole Robinson , qemu-devel@nongnu.org Cc: qemu-trivial@nongnu.org On 02/11/2015 16:18, Cole Robinson wrote: >> > - if ((access(un.sun_path, F_OK) == 0) && >> > - unlink(un.sun_path) < 0) { >> > + if (unlink(un.sun_path) < 0) { >> > error_setg_errno(errp, errno, >> > "Failed to unlink socket %s", un.sun_path); >> > goto err; >> > > This is a serious semantic change, after this patch you will get: > > $ ./x86_64-softmmu/qemu-system-x86_64 -vnc unix:/tmp/idontexist.sock > qemu-system-x86_64: -vnc unix:/tmp/idontexist.sock: Failed to start VNC > server: Failed to unlink socket /tmp/idontexist.sock: No such file or directory > > Previously it would 'just work'. Common libvirt usage depends on this as well > > Yeah there's a TOCTTOU race here, but it's very minor: if sun_path is created > after the access() check, qemu is just going to fail to start since bind() > will barf if the unix socket path exists. You're right. I misread how to test the change. The right change is what Markus proposed. Paolo