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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 05/20] tomoyo_write_control(): get rid of pointless access_ok()
Date: Sat, 9 May 2020 17:57:56 -0700	[thread overview]
Message-ID: <CAHk-=wgqyW2ow6yO+yz_0v4aKd162Lwtr24c5nKjZRG-2vW8PA@mail.gmail.com> (raw)
In-Reply-To: <b67a5f6e-0192-f350-e797-455fe570ce93@i-love.sakura.ne.jp>

On Sat, May 9, 2020 at 5:51 PM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> I think that this access_ok() check helps reducing partial writes (either
> "whole amount was processed" or "not processed at all" unless -ENOMEM).

No it doesn't.

"access_ok()" only checks the range being a valid user address range.

It doesn't actually help at all if the worry is "what if we take a
page fault in the middle".  Because it simply doesn't check those
kinds of things.

Now, if somebody passes actual invalid ranges (ie kernel addresses or
other crazy stuff), they only have themselves to blame. The invalid
range will be noticed when actually doing the user copy, and then
you'll get EFAULT there. But there's no point in trying to figure that
out early - it's only adding overhead, and it doesn't help any normal
case.

                  Linus

  reply	other threads:[~2020-05-10  0:58 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-09 23:41 [PATCHES] uaccess simple access_ok() removals Al Viro
2020-05-09 23:45 ` [PATCH 01/20] dlmfs_file_write(): get rid of pointless access_ok() Al Viro
2020-05-09 23:45   ` [PATCH 02/20] fat_dir_ioctl(): hadn't needed that access_ok() for more than a decade Al Viro
2020-05-09 23:45   ` [PATCH 03/20] btrfs_ioctl_send(): don't bother with access_ok() Al Viro
2020-05-09 23:45   ` [PATCH 04/20] FIEMAP: " Al Viro
2020-05-10  7:02     ` Christoph Hellwig
2020-05-13 19:02       ` Al Viro
2020-05-13 19:38         ` Christoph Hellwig
2020-05-29 15:01           ` Al Viro
2020-05-09 23:45   ` [PATCH 05/20] tomoyo_write_control(): get rid of pointless access_ok() Al Viro
2020-05-10  0:50     ` Tetsuo Handa
2020-05-10  0:57       ` Linus Torvalds [this message]
2020-05-10  1:04         ` Tetsuo Handa
2020-05-10  3:01         ` Al Viro
2020-05-09 23:45   ` [PATCH 06/20] n_hdlc_tty_read(): remove " Al Viro
2020-05-15 10:53     ` Greg Kroah-Hartman
2020-05-09 23:45   ` [PATCH 07/20] nvram: drop useless access_ok() Al Viro
2020-05-15 10:54     ` Greg Kroah-Hartman
2020-05-09 23:45   ` [PATCH 08/20] cm4000_cs.c cmm_ioctl(): get rid of pointless access_ok() Al Viro
2020-05-09 23:45   ` [PATCH 09/20] drivers/fpga/dfl-fme-pr.c: " Al Viro
2020-05-09 23:45   ` [PATCH 10/20] drivers/fpga/dfl-afu-dma-region.c: " Al Viro
2020-05-09 23:45   ` [PATCH 11/20] amifb: get rid of pointless access_ok() calls Al Viro
2020-05-14 13:45     ` Bartlomiej Zolnierkiewicz
2020-05-14 14:07       ` Al Viro
2020-05-14 14:25         ` Bartlomiej Zolnierkiewicz
2020-05-14 17:41           ` Al Viro
2020-05-14 20:21             ` Geert Uytterhoeven
2020-05-09 23:45   ` [PATCH 12/20] omapfb: " Al Viro
2020-05-14 13:39     ` Bartlomiej Zolnierkiewicz
2020-05-09 23:45   ` [PATCH 13/20] drivers/crypto/ccp/sev-dev.c: get rid of pointless access_ok() Al Viro
2020-05-09 23:45   ` [PATCH 14/20] via-pmu: don't bother with access_ok() Al Viro
2020-05-09 23:45   ` [PATCH 15/20] drm_read(): get rid of pointless access_ok() Al Viro
2020-05-09 23:45   ` [PATCH 16/20] efi_test: " Al Viro
2020-05-09 23:45   ` [PATCH 17/20] lpfc_debugfs: " Al Viro
2020-05-09 23:45   ` [PATCH 18/20] usb: get rid of pointless access_ok() calls Al Viro
2020-05-15 10:53     ` Greg Kroah-Hartman
2020-05-09 23:45   ` [PATCH 19/20] hfi1: get rid of pointless access_ok() Al Viro
2020-05-09 23:45   ` [PATCH 4/4] vmci_host: " Al Viro
2020-05-15 10:53     ` Greg Kroah-Hartman
2020-05-10  0:34 ` [PATCHES] uaccess simple access_ok() removals Linus Torvalds
2020-05-10  3:27   ` Al Viro
2020-05-10 14:34 ` David Laight

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