netdev - Re: [bug report] dead loop in generic_perform_write() //Re: [PATCH v7 07/12] iov

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]

Message-ID: <CAHk-=wjSjuDrS9gc191PTEDDow7vHy6Kd3DKDaG+KVH0NQ3v=w@mail.gmail.com>
Date: Wed, 28 Feb 2024 14:57:00 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Tong Tiangen <tongtiangen@...wei.com>
Cc: David Howells <dhowells@...hat.com>, Jens Axboe <axboe@...nel.dk>, 
	Al Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@....de>, 
	Christian Brauner <christian@...uner.io>, David Laight <David.Laight@...lab.com>, 
	Matthew Wilcox <willy@...radead.org>, Jeff Layton <jlayton@...nel.org>, linux-fsdevel@...r.kernel.org, 
	linux-block@...r.kernel.org, linux-mm@...ck.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [bug report] dead loop in generic_perform_write() //Re: [PATCH v7
 07/12] iov_iter: Convert iterate*() to inline funcs

On Wed, 28 Feb 2024 at 13:21, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Hmm. If the copy doesn't succeed and make any progress at all, then
> the code in generic_perform_write() after the "goto again"
>
>                 //[4]
>                 if (unlikely(fault_in_iov_iter_readable(i, bytes) ==
>                               bytes)) {
>
> should break out of the loop.

Ahh. I see the problem. Or at least part of it.

The iter is an ITER_BVEC.

And fault_in_iov_iter_readable() "knows" that an ITER_BVEC cannot
fail. Because obviously it's a kernel address, so no user page fault.

But for the machine check case, ITER_BVEC very much can fail.

This should never have worked in the first place.

What a crock.

Do we need to make iterate_bvec() always succeed fully, and make
copy_mc_to_kernel() zero out the end?

                   Linus