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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>
Subject: Re: [RFC][PATCHES] iov_iter.c rewrite
Date: Mon, 8 Dec 2014 10:37:51 -0800	[thread overview]
Message-ID: <CA+55aFxrrTV-xBbvEzVKsXRVKyvZhQZj-6BNDpTsG4J5k6CJEg@mail.gmail.com> (raw)
In-Reply-To: <20141208182012.GE22149@ZenIV.linux.org.uk>

On Mon, Dec 8, 2014 at 10:20 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> I certainly had missed that insanity during the analysis - we don't do
> a lot of O_DIRECT IO to/from kernel addresses of any sort...  This
> codepath allows it ;-/  Ability to trigger it is equivalent to ability
> to run any code in kernel mode, so it's not an additional security hole,
> but...

Is there any chance we could just return EINVAL for this case?

Who does O_DIRECT on module load anyway? If this is only for
finit_module(), that uses "kernel_read()", and maybe we could just
make sure that the kernel_read() function never ever uses the
direct-IO paths?

[ Time passes, I look at the code ]

Oh crap. So the reason it triggers seems to be that we basically get a
random file descriptor that we didn't open, and then we have

  vfs_read() ->
  xfs_file_operations->read() ->
  ew_sync_read() ->
  xfs_file_operations->read_iter()
  xfs_file_read_iter()

and we are stuck with this iterator that really just wants to do copies.

How about we make "kernel_read()" just clear O_DIRECT? Does that fix
it to just use copies?

                      Linus

  reply	other threads:[~2014-12-08 18:37 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-04 20:20 [RFC][PATCHES] iov_iter.c rewrite Al Viro
2014-12-04 20:23 ` [RFC][PATCH 01/13] iov_iter.c: macros for iterating over iov_iter Al Viro
2014-12-04 20:23 ` [RFC][PATCH 02/13] iov_iter.c: iterate_and_advance Al Viro
2014-12-04 20:23 ` [RFC][PATCH 03/13] iov_iter.c: convert iov_iter_npages() to iterate_all_kinds Al Viro
2014-12-04 20:23 ` [RFC][PATCH 04/13] iov_iter.c: convert iov_iter_get_pages() " Al Viro
2014-12-04 20:23 ` [RFC][PATCH 05/13] iov_iter.c: convert iov_iter_get_pages_alloc() " Al Viro
2014-12-04 20:23 ` [RFC][PATCH 06/13] iov_iter.c: convert iov_iter_zero() to iterate_and_advance Al Viro
2014-12-04 20:23 ` [RFC][PATCH 07/13] iov_iter.c: get rid of bvec_copy_page_{to,from}_iter() Al Viro
2014-12-05 12:28   ` Sergei Shtylyov
2014-12-04 20:23 ` [RFC][PATCH 08/13] iov_iter.c: convert copy_from_iter() to iterate_and_advance Al Viro
2014-12-04 20:23 ` [RFC][PATCH 09/13] iov_iter.c: convert copy_to_iter() " Al Viro
2014-12-04 20:23 ` [RFC][PATCH 10/13] iov_iter.c: handle ITER_KVEC directly Al Viro
2014-12-04 20:23 ` [RFC][PATCH 11/13] csum_and_copy_..._iter() Al Viro
2014-12-04 20:23 ` [RFC][PATCH 12/13] new helper: iov_iter_kvec() Al Viro
2014-12-04 20:23 ` [RFC][PATCH 13/13] copy_from_iter_nocache() Al Viro
2014-12-08 16:46 ` [RFC][PATCHES] iov_iter.c rewrite Kirill A. Shutemov
2014-12-08 17:58   ` Al Viro
2014-12-08 18:08     ` Al Viro
2014-12-08 18:14       ` Linus Torvalds
2014-12-08 18:20         ` Al Viro
2014-12-08 18:37           ` Linus Torvalds [this message]
2014-12-08 18:46             ` Al Viro
2014-12-08 18:57               ` Linus Torvalds
2014-12-08 19:28                 ` Al Viro
2014-12-08 19:48                   ` Linus Torvalds
2014-12-09  1:56                   ` Al Viro
2014-12-09  2:21                     ` Kirill A. Shutemov
2015-04-01  2:33                 ` [RFC] iov_iter_get_pages() semantics Al Viro
2015-04-01 16:45                   ` Linus Torvalds
2015-04-01 18:08                     ` Al Viro
2015-04-01 18:15                       ` Linus Torvalds
2015-04-01 19:23                         ` Al Viro
2015-04-01 18:26                       ` Linus Torvalds
2015-04-01 18:34                         ` Linus Torvalds
2015-04-01 20:15                           ` Al Viro
2015-04-01 21:57                             ` Linus Torvalds
2015-04-01 19:50                         ` Al Viro
2014-12-08 18:56     ` [RFC][PATCHES] iov_iter.c rewrite Kirill A. Shutemov
2014-12-08 19:01       ` Linus Torvalds
2014-12-08 19:15         ` Dave Jones
2014-12-08 19:23         ` Kirill A. Shutemov
2014-12-08 22:14           ` Theodore Ts'o
2014-12-08 22:23             ` Linus Torvalds
2014-12-08 22:31               ` Dave Jones
2014-12-08 18:07   ` Linus Torvalds
2014-12-08 18:14     ` Al Viro
2014-12-08 18:23       ` Linus Torvalds
2014-12-08 18:35         ` Al Viro

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