From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rich Felker Subject: Re: [PATCHv10 man-pages 5/5] execveat.2: initial man page for execveat(2) Date: Fri, 9 Jan 2015 17:42:52 -0500 Message-ID: <20150109224252.GY4574@brightrain.aerifal.cx> References: <20150109161302.GQ4574@brightrain.aerifal.cx> <20150109204815.GR4574@brightrain.aerifal.cx> <20150109205626.GK22149@ZenIV.linux.org.uk> <20150109205926.GT4574@brightrain.aerifal.cx> <20150109210941.GL22149@ZenIV.linux.org.uk> <20150109212852.GU4574@brightrain.aerifal.cx> <20150109215042.GM22149@ZenIV.linux.org.uk> <20150109221728.GW4574@brightrain.aerifal.cx> <20150109223300.GO22149@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150109223300.GO22149@ZenIV.linux.org.uk> Sender: sparclinux-owner@vger.kernel.org To: Al Viro Cc: David Drysdale , "Michael Kerrisk (man-pages)" , "Eric W. Biederman" , Andy Lutomirski , Meredydd Luff , "linux-kernel@vger.kernel.org" , Andrew Morton , David Miller , Thomas Gleixner , Stephen Rothwell , Oleg Nesterov , Ingo Molnar , "H. Peter Anvin" , Kees Cook , Arnd Bergmann , Christoph Hellwig , X86 ML , linux-arch , Linux API , sparclinux@vger.kernel.org List-Id: linux-api@vger.kernel.org On Fri, Jan 09, 2015 at 10:33:00PM +0000, Al Viro wrote: > On Fri, Jan 09, 2015 at 05:17:28PM -0500, Rich Felker wrote: > > > Back then the procfs-free environments had been pushed as a serious argument > > > in favour of merging the damn thing. Now you guys turn around and say that > > > we not only need procfs mounted, we need a yet-to-be-added kludge in there > > > to cope with the actual intended uses. > > > > Reverting does not fix the problem. There is no way to make fexecve > > work for scripts without kernel support, and the needed kernel support > > without fexecve would be even nastier, since handling of /proc/self/fd > > magic-symlinks would need to be special-cased. The added fexecveat > > syscall supports fully /proc-less operation for non-scripts. > > Oh, yes it does. It's not *our* problem if it's out of tree and not > a part of ABI. That way if you need it, *you* get to come up with clean > implementation. If it's in-tree you get leverage to push ugly kludges > further in. And frankly, I don't trust you to abstain from using that > leverage in rather nasty ways. > > Out of curiosity, how would you expect that "open only once" to work? > All reliable variants I see are beyond sick... Here's a very simple way it could work -- it could put the O_PATH fd on a previously-unused fd number, and put a special flag on the fd, like FD_CLOEXEC, but that causes the kernel to close it whenever it's opened. The pathname passed could then simply be /dev/fd/%d or /proc/self/fd/%d, and although this is presently dependent on /proc being mounted, virtual /dev/fd/* could someday be something completely independent of procfs. The kernel keeps all the freedom to choose how to pass the name to the interpreter. I'm not proposing any kernel API/ABI lock-in and I'm with you in opposing such lock-in. Rich