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Date: Thu, 21 May 2020 22:28:39 -0500 From: ebiederm@...ssion.com (Eric W. Biederman) To: Rob Landley <rob@...dley.net> Cc: linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>, Kees Cook <keescook@...omium.org>, Greg Ungerer <gerg@...ux-m68k.org>, Bernd Edlinger <bernd.edlinger@...mail.de>, linux-fsdevel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>, Alexey Dobriyan <adobriyan@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Casey Schaufler <casey@...aufler-ca.com>, linux-security-module@...r.kernel.org, James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, Andy Lutomirski <luto@...capital.net> Subject: Re: [PATCH v2 7/8] exec: Generic execfd support Rob Landley <rob@...dley.net> writes: > On 5/20/20 11:05 AM, Eric W. Biederman wrote: > Toybox would _like_ proc mounted, but can't assume it. I'm writing a new > bash-compatible shell with nommu support, which means in order to do subshell > and background tasks if (!CONFIG_FORK) I need to create a pipe pair, vfork(), > have the child exec itself to unblock the parent, and then read the context data > that just got discarded through the pipe from the parent. ("Wheee." And you can > quote me on that.) Do you have clone(CLONE_VM) ? If my quick skim of the kernel sources is correct that should be the same as vfork except without causing the parent to wait for you. Which I think would remove the need to reexec yourself. >> The file descriptor is stored in mm->exe_file. >> Probably the most straight forward implementation is to allow >> execveat(AT_EXE_FILE, ...). > > Cool, that works. > >> You can look at binfmt_misc for how to reopen an open file descriptor. > > Added to the todo heap. Yes I don't think it would be a lot of code. I think you might be better served with clone(CLONE_VM) as it doesn't block so you don't need to feed yourself your context over a pipe. Eric
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