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Re: [PATCH] fix fault_in_multipages_...() on architectures with no-op access_ok()

From Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups linux.kernel
Subject Re: [PATCH] fix fault_in_multipages_...() on architectures with no-op access_ok()
Date 2016-09-20 22:50 +0200
Message-ID <sjA9j-7XM-1@gated-at.bofh.it> (permalink)
References (1 earlier) <sjuQh-4Gm-1@gated-at.bofh.it> <sjwS5-5V7-11@gated-at.bofh.it> <sjyAx-74A-11@gated-at.bofh.it> <sjzPY-7R6-15@gated-at.bofh.it> <sjzZD-7Uq-13@gated-at.bofh.it>
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On Tue, Sep 20, 2016 at 1:38 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> Not the point.  Of course it *would* fail; the problem is that the loop
> that would ping each page is never executed.

You're missing the point.

If "access_ok()" is fine with wrapping, then some otehr system call
that wraps will successfully do a memcpy_from/to_user() with a wrapped
address (and the proper mappings). Which is completely bogus.

So access_ok() should be fixed regardless. An access_ok() that accepts
a wrapping address is a bug. End of story.

And once that bug is fixed, the fault_in_multipages..() issue is moot.
So it shouldn't be an issue.

             Linus

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Thread

[bug] pwritev02 hang on s390x with 4.8.0-rc7 Jan Stancek <jstancek@redhat.com> - 2016-09-20 15:00 +0200
  Re: [bug] pwritev02 hang on s390x with 4.8.0-rc7 Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 17:10 +0200
    Re: [bug] pwritev02 hang on s390x with 4.8.0-rc7 Jan Stancek <jstancek@redhat.com> - 2016-09-20 19:20 +0200
      Re: [bug] pwritev02 hang on s390x with 4.8.0-rc7 Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 19:40 +0200
      [PATCH] fix fault_in_multipages_...() on architectures with no-op  access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 21:10 +0200
        Re: [PATCH] fix fault_in_multipages_...() on architectures with no-op access_ok() Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-20 22:30 +0200
          Re: [PATCH] fix fault_in_multipages_...() on architectures with  no-op access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 22:40 +0200
            Re: [PATCH] fix fault_in_multipages_...() on architectures with no-op access_ok() Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-20 22:50 +0200
              Re: [PATCH] fix fault_in_multipages_...() on architectures with  no-op access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 23:10 +0200
                Re: [PATCH] fix fault_in_multipages_...() on architectures with  no-op access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-20 23:40 +0200
                Re: [PATCH] fix fault_in_multipages_...() on architectures with no-op access_ok() Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-21 01:50 +0200
                Re: [PATCH] fix fault_in_multipages_...() on architectures with  no-op access_ok() Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-21 02:40 +0200

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