From: David Hildenbrand <david@redhat.com>
To: Andy Lutomirski <luto@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
"David Laight" <David.Laight@aculab.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
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Subject: Re: [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE
Date: Thu, 26 Aug 2021 23:47:07 +0200 [thread overview]
Message-ID: <0ed69079-9e13-a0f4-776c-1f24faa9daec@redhat.com> (raw)
In-Reply-To: <b60e9bd1-7232-472d-9c9c-1d6593e9e85e@www.fastmail.com>
On 26.08.21 19:48, Andy Lutomirski wrote:
> On Fri, Aug 13, 2021, at 5:54 PM, Linus Torvalds wrote:
>> On Fri, Aug 13, 2021 at 2:49 PM Andy Lutomirski <luto@kernel.org> wrote:
>>>
>>> I’ll bite. How about we attack this in the opposite direction: remove the deny write mechanism entirely.
>>
>> I think that would be ok, except I can see somebody relying on it.
>>
>> It's broken, it's stupid, but we've done that ETXTBUSY for a _loong_ time.
>
> Someone off-list just pointed something out to me, and I think we should push harder to remove ETXTBSY. Specifically, we've all been focused on open() failing with ETXTBSY, and it's easy to make fun of anyone opening a running program for write when they should be unlinking and replacing it.
>
> Alas, Linux's implementation of deny_write_access() is correct^Wabsurd, and deny_write_access() *also* returns ETXTBSY if the file is open for write. So, in a multithreaded program, one thread does:
>
> fd = open("some exefile", O_RDWR | O_CREAT | O_CLOEXEC);
> write(fd, some stuff);
>
> <--- problem is here
>
> close(fd);
> execve("some exefile");
>
> Another thread does:
>
> fork();
> execve("something else");
>
> In between fork and execve, there's another copy of the open file description, and i_writecount is held, and the execve() fails. Whoops. See, for example:
>
> https://github.com/golang/go/issues/22315
>
> I propose we get rid of deny_write_access() completely to solve this.
>
> Getting rid of i_writecount itself seems a bit harder, since a handful of filesystems use it for clever reasons.
>
> (OFD locks seem like they might have the same problem. Maybe we should have a clone() flag to unshare the file table and close close-on-exec things?)
>
It's not like this issue is new (^2017) or relevant in practice. So no
need to hurry IMHO. One step at a time: it might make perfect sense to
remove ETXTBSY, but we have to be careful to not break other user space
that actually cares about the current behavior in practice.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-08-26 21:47 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-12 8:43 [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE 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
[not found] ` <87h7ft2j68.fsf@disp2133>
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 [this message]
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
[not found] ` <162943109106.9892.7426782042253067338@noble.neil.brown.name>
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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