netdev - Re: [RFC PATCH 0/4] splice: Fix corruption in data spliced to pipe

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: Thu, 29 Jun 2023 14:05:16 -0400
From: Matt Whitlock <kernel@...twhitlock.name>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: David Howells <dhowells@...hat.com>,
 <netdev@...r.kernel.org>,
 Matthew Wilcox <willy@...radead.org>,
 Dave Chinner <david@...morbit.com>,
 Jens Axboe <axboe@...nel.dk>,
 <linux-fsdevel@...ck.org>,
 <linux-mm@...ck.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/4] splice: Fix corruption in data spliced to pipe

On Thursday, 29 June 2023 13:56:04 EDT, Linus Torvalds wrote:
> On Thu, 29 Jun 2023 at 08:55, David Howells <dhowells@...hat.com> wrote:
>> 
>> Matt Whitlock, Matthew Wilcox and Dave Chinner are of the 
>> opinion that data
>> in the pipe must not be seen to change and that if it does, this is a bug.
>
> I'm not convinced.
>
> The whole *point* of vmsplice (and splicing from a file) is the zero-copy.
>
> If you don't want the zero-copy, then you should use just "write()".

If you want zero copies, then call splice() *with* SPLICE_F_MOVE.

If you want one copy (kernel-to-kernel), then call splice() *without* 
SPLICE_F_MOVE.

If you want two copies (kernel-to-user + user-to-kernel), call read() and 
write().

I don't know why SPLICE_F_MOVE is being ignored in this thread. Sure, maybe 
the way it has historically been implemented was only relevant when the 
input FD is a pipe, but that's not what the man page implies. You have the 
opportunity to make it actually do what it says on the tin.