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Peter Anvin" , Al Viro , Li Chen , Cong Wang , linux-arch , LKML , linux-fsdevel , linux-api , Arnd Bergmann , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Jan Kara , Jonathan Corbet , Shuah Khan , Kees Cook , Sergei Zimmerman , Farid Zakaria Subject: Re: [RFC] Null Namespaces Message-ID: Mail-Followup-To: Jori Koolstra , Christian Brauner , John Ericson , "H. Peter Anvin" , Al Viro , Li Chen , Cong Wang , linux-arch , LKML , linux-fsdevel , linux-api , Arnd Bergmann , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Jan Kara , Jonathan Corbet , Shuah Khan , Kees Cook , Sergei Zimmerman , Farid Zakaria References: <20260624231219.GL2636677@ZenIV> <29cd3188-2d7c-4470-a39a-6648638f795e@zytor.com> <614b290f-e274-4eb2-b687-008b004de526@app.fastmail.com> <20260629-zoomen-tragweite-redakteur-dc6c41c9c151@brauner> Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260629-zoomen-tragweite-redakteur-dc6c41c9c151@brauner> On Mon, Jun 29, 2026 at 12:39:56PM +0200, Christian Brauner wrote: > > The kernel rightfully has consolidated path resolution in a few key > > places as much as possible -- the internal `struct path` does not suffer > > from these issues. I barely modify those places to support null root and > > CWD, and because of that consolidation, we shouldn't expect new places > > to crop up in the future. (Duplicative path resolution logic is a bad > > idea whether or not we have a nascent, little-used NULL-cwd/root code > > path.) Therefore, I think existing code review, even among people > > totally ignorant of this feature, will protect us --- the vast majority > > of code will just be working with `struct path`, and be totally > > unaffected by this change. > > I actually did laugh out loud reading this. I'm sorry, I can't really > take this argument seriously. May I introduce you to drivers/ for a > start and the history of path lookup exploits of the last - say 10 > years. > > You have to excuse me but it's a mixture of amusement and slight anger. > Amusement because this is really naive and thus also a bit endearing. > Anger because it single-handedly dismisses how big of an attack surface > and problem space path lookup is. The equivalent of every math > professor's "trivial. excercise left to the reader". I could easily show you why path lookup is trivial, but I have no space left in the margins of this email.