From: "NeilBrown" <neilb@suse.de>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: "Andy Lutomirski" <luto@kernel.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
"David Laight" <David.Laight@aculab.com>,
"David Hildenbrand" <david@redhat.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Alexey Dobriyan" <adobriyan@gmail.com>,
"Steven Rostedt" <rostedt@goodmis.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
"Arnaldo Carvalho de Melo" <acme@kernel.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
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"Namhyung Kim" <namhyung@kernel.org>,
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"Sergey Senozhatsky" <sergey.senozhatsky@gmail.com>,
"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
"Kees Cook" <keescook@chromium.org>,
"Greg Ungerer" <gerg@linux-m68k.org>,
"Geert Uytterhoeven" <geert@linux-m68k.org>,
"Mike Rapoport" <rppt@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Vincenzo Frascino" <vincenzo.frascino@arm.com>,
"Chinwen Chang" <chinwen.chang@mediatek.com>,
"Michel Lespinasse" <walken@google.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
"Huang Ying" <ying.huang@intel.com>,
"Jann Horn" <jannh@google.com>, "Feng Tang" <feng.tang@intel.com>,
"Kevin Brodsky" <Kevin.Brodsky@arm.com>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Shawn Anastasio" <shawn@anastas.io>
Subject: Re: [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE
Date: Fri, 20 Aug 2021 13:44:51 +1000 [thread overview]
Message-ID: <162943109106.9892.7426782042253067338@noble.neil.brown.name> (raw)
In-Reply-To: <20210818154217.GB24115@fieldses.org>
On Thu, 19 Aug 2021, J. Bruce Fields wrote:
> On Fri, Aug 13, 2021 at 05:49:19PM -0700, Andy Lutomirski wrote:
> > I’ll bite. How about we attack this in the opposite direction: remove
> > the deny write mechanism entirely.
>
> For what it's worth, Windows has open flags that allow denying read or
> write opens. They also made their way into the NFSv4 protocol, but
> knfsd enforces them only against other NFSv4 clients. Last I checked,
> Samba attempted to emulate them using flock (and there's a comment to
> that effect on the flock syscall in fs/locks.c). I don't know what Wine
> does.
>
> Pavel Shilovsky posted flags adding O_DENY* flags years ago:
>
> https://lwn.net/Articles/581005/
>
> I keep thinking I should look back at those some day but will probably
> never get to it.
O_DENYREAD is an insane flag. If a process reads a file that some other
process is working on, then the only which could be hurt is the reader.
So allowing a process to ask for the open to fail if someone is writing
might make sense. Insisting that all opens fail does not.
Any code wanting O_DENYREAD *should* use advisory locking, and any code
wanting to know about read denial should too.
O_DENYWRITE can make sense. When combined with a O_RDONLY open it is
effectively what happens when you exec a program. You can no longer
open that file for write - you get ETXTBSY.
It would be nice to be able to combine O_DENYWRITE with O_RDWR. This
combination is exactly what the kernel *should* do for swap files.
Unfortunately it doesn't. The "i_writecount" field that is used to
trigger ETXTBSY for executables doesn't work for the single-writer
model.
I'm not sure about O_DENYDELETE. It is a lock on the name. Unix has
traditionally used lock-files to lock a name. The functionality makes
sense for processes with write-access to the directory...
NeilBrown
next prev parent reply other threads:[~2021-08-20 3:45 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-12 8:43 David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 1/7] binfmt: don't use MAP_DENYWRITE when loading shared libraries via uselib() David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 2/7] kernel/fork: factor out atomcially replacing the current MM exe_file David Hildenbrand
2021-08-12 9:17 ` Christian Brauner
2021-08-12 8:43 ` [PATCH v1 3/7] kernel/fork: always deny write access to " David Hildenbrand
2021-08-12 10:05 ` Christian Brauner
2021-08-12 10:13 ` David Hildenbrand
2021-08-12 12:32 ` Christian Brauner
2021-08-12 12:38 ` David Hildenbrand
2021-08-12 16:51 ` Linus Torvalds
2021-08-12 19:38 ` David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 4/7] binfmt: remove in-tree usage of MAP_DENYWRITE David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 5/7] mm: remove VM_DENYWRITE David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 6/7] mm: ignore MAP_DENYWRITE in ksys_mmap_pgoff() David Hildenbrand
2021-08-12 8:43 ` [PATCH v1 7/7] fs: update documentation of get_write_access() and friends David Hildenbrand
2021-08-12 12:20 ` [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE Florian Weimer
2021-08-12 12:47 ` David Hildenbrand
2021-08-12 16:17 ` Eric W. Biederman
2021-08-12 17:32 ` Eric W. Biederman
2021-08-12 17:35 ` Andy Lutomirski
2021-08-12 17:48 ` Eric W. Biederman
2021-08-12 18:01 ` Andy Lutomirski
2021-08-12 18:10 ` Linus Torvalds
2021-08-12 18:47 ` Eric W. Biederman
2021-08-13 9:05 ` David Laight
2021-08-13 20:17 ` Eric W. Biederman
2021-08-13 20:51 ` Florian Weimer
2021-08-14 0:31 ` Linus Torvalds
2021-08-14 0:49 ` Andy Lutomirski
2021-08-14 0:54 ` Linus Torvalds
2021-08-14 0:58 ` Linus Torvalds
2021-08-14 1:57 ` Al Viro
2021-08-14 2:02 ` Al Viro
2021-08-14 9:06 ` David Hildenbrand
2021-08-14 7:53 ` Christian Brauner
2021-08-14 19:52 ` David Laight
2021-08-26 17:48 ` Andy Lutomirski
2021-08-26 21:47 ` David Hildenbrand
2021-08-26 22:13 ` Eric W. Biederman
2021-08-27 8:22 ` David Laight
2021-08-27 15:58 ` Eric W. Biederman
2021-09-01 8:28 ` David Hildenbrand
2021-08-27 10:18 ` Christian Brauner
2021-08-14 3:04 ` Matthew Wilcox
2021-08-17 16:48 ` Removing Mandatory Locks Eric W. Biederman
2021-08-17 16:50 ` David Hildenbrand
2021-08-18 9:34 ` Rodrigo Campos
2021-08-19 19:18 ` Jeff Layton
2021-08-19 20:03 ` Willy Tarreau
2021-08-19 18:39 ` Jeff Layton
2021-08-19 19:15 ` Linus Torvalds
2021-08-19 19:55 ` Eric Biggers
2021-08-19 20:18 ` Jeff Layton
2021-08-19 20:31 ` Linus Torvalds
2021-08-19 21:43 ` Jeff Layton
2021-08-19 22:32 ` Linus Torvalds
2021-08-20 8:30 ` David Laight
2021-08-23 7:55 ` Geert Uytterhoeven
2021-08-23 8:14 ` David Laight
2021-08-20 13:43 ` Steven Rostedt
2021-08-20 16:06 ` Linus Torvalds
2021-08-20 2:10 ` Matthew Wilcox
2021-08-20 6:36 ` Amir Goldstein
2021-08-20 7:14 ` Amir Goldstein
2021-08-20 12:27 ` Jeff Layton
2021-08-20 12:38 ` Willy Tarreau
2021-08-20 13:03 ` Jeff Layton
2021-08-20 13:11 ` Willy Tarreau
2021-08-20 16:30 ` Kees Cook
2021-08-20 19:17 ` H. Peter Anvin
2021-08-20 21:29 ` Jeff Layton
2021-08-21 12:45 ` Jeff Layton
2021-08-23 22:15 ` J. Bruce Fields
2021-08-20 22:31 ` Matthew Wilcox
2021-08-18 7:51 ` [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE Christian Brauner
2021-08-18 15:42 ` J. Bruce Fields
2021-08-19 13:56 ` Eric W. Biederman
2021-08-19 14:33 ` J. Bruce Fields
2021-08-20 12:54 ` Jeff Layton
2021-08-20 3:44 ` NeilBrown [this message]
2021-08-20 8:25 ` David Laight
2021-08-12 19:24 ` David Hildenbrand
2021-08-12 18:15 ` Florian Weimer
2021-08-12 18:21 ` Linus Torvalds
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