linux-kernel - Re: [PATCH v1 0/7] Remove in-tree usage of MAP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 27 Aug 2021 10:58:32 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     David Laight <David.Laight@...LAB.COM>
Cc:     David Hildenbrand <david@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Steven Rostedt" <rostedt@...dmis.org>,
        "Peter Zijlstra \(Intel\)" <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        "Namhyung Kim" <namhyung@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        "Sergey Senozhatsky" <sergey.senozhatsky@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Kees Cook <keescook@...omium.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Mike Rapoport" <rppt@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Vincenzo Frascino" <vincenzo.frascino@....com>,
        Chinwen Chang <chinwen.chang@...iatek.com>,
        Michel Lespinasse <walken@...gle.com>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Matthew Wilcox \(Oracle\)" <willy@...radead.org>,
        Huang Ying <ying.huang@...el.com>,
        Jann Horn <jannh@...gle.com>, Feng Tang <feng.tang@...el.com>,
        Kevin Brodsky <Kevin.Brodsky@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Shawn Anastasio" <shawn@...stas.io>,
        Steven Price <steven.price@....com>,
        "Nicholas Piggin" <npiggin@...il.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Jens Axboe <axboe@...nel.dk>,
        "Gabriel Krisman Bertazi" <krisman@...labora.com>,
        Peter Xu <peterx@...hat.com>,
        "Suren Baghdasaryan" <surenb@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        "Marco Elver" <elver@...gle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Nicolas Viennot <Nicolas.Viennot@...sigma.com>,
        Thomas Cedeno <thomascedeno@...gle.com>,
        Collin Fijalkovich <cfijalkovich@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Chengguang Xu <cgxu519@...ernel.net>,
        Christian König 
        <ckoenig.leichtzumerken@...il.com>,
        "linux-unionfs\@vger.kernel.org" <linux-unionfs@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "the arch\/x86 maintainers" <x86@...nel.org>,
        "linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        "Florian Weimer" <fweimer@...hat.com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE

David Laight <David.Laight@...LAB.COM> writes:

> From: Eric W. Biederman
>> Sent: 26 August 2021 23:14
> ...
>> I also ran into this issue not too long ago when I refactored the
>> usermode_driver code.  My challenge was not being in userspace
>> the delayed fput was not happening in my kernel thread.  Which meant
>> that writing the file, then closing the file, then execing the file
>> consistently reported -ETXTBSY.
>> 
>> The kernel code wound up doing:
>> 	/* Flush delayed fput so exec can open the file read-only */
>> 	flush_delayed_fput();
>> 	task_work_run();
>> 
>> As I read the code the delay for userspace file descriptors is
>> always done with task_work_add, so userspace should not hit
>> that kind of silliness, and should be able to actually close
>> the file descriptor before the exec.
>
> If task_work_add ends up adding it to a task that is already
> running on a different cpu, and that cpu takes a hardware
> interrupt that takes some time and/or schedules the softint
> code to run immediately the hardware interrupt completes
> then it may well be possible for userspace to have 'issues'.

It it task_work_add(current).  Which punts the work to the return to
userspace.

> Any flags associated with O_DENY_WRITE would need to be cleared
> synchronously in the close() rather then in any delayed fput().

Eric