Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened usercopy feature

From	Jiri Olsa <jolsa@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened usercopy feature
Date	2016-09-07 21:30 +0200
Message-ID	<seQHM-3XU-23@gated-at.bofh.it> (permalink)
References	(2 earlier) <sdXLk-1lQ-5@gated-at.bofh.it> <sesPd-55p-11@gated-at.bofh.it> <seFCF-59y-17@gated-at.bofh.it> <seO3g-298-31@gated-at.bofh.it> <seOmC-2g5-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, Sep 07, 2016 at 09:58:01AM -0700, Linus Torvalds wrote:
> On Wed, Sep 7, 2016 at 9:38 AM, Andi Kleen <andi@firstfloor.org> wrote:
> >>
> >> -                             n = copy_to_user(buffer, (char *)start, tsz);
> >> +                             buf = kzalloc(tsz, GFP_KERNEL);
> >
> > You have to add some limit and a loop, otherwise a user can eat all kernel memory,
> > or copies > KMALLOC_MAX wouldn't work. Probably only get a single page.
> 
> 'start' and 'tsz' is already chunked to be aligned pages (well, as
> aligned as they can be: the beginning and end obviously won't be).
> Above the loop:
> 
>         if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
>                 tsz = buflen;
> 
> and then inside the loop:
> 
>                 tsz = (buflen > PAGE_SIZE ? PAGE_SIZE : buflen);
> 
> so it's already limited to one page.
> 
> That said, it *might* be worth moving the temporary allocation to the
> top, or even to move it to open_kcore(). It used to be a special case
> for just the vmalloc region, now it's always done.
> 
> So instead of having two different copies of the same special case for
> the two different cases, why not try to unify them and just have one
> common (page-sized) buffer allocation?

ook, sounds good.. will repost soon

jirka

Thread

[PATCH] fs/proc/kcore.c: Omit kernel text area for hardened usercopy feature Jiri Olsa <jolsa@kernel.org> - 2016-09-02 14:30 +0200
  Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Andi Kleen <andi@firstfloor.org> - 2016-09-02 17:20 +0200
    Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Jiri Olsa <jolsa@redhat.com> - 2016-09-02 18:20 +0200
    Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Jiri Olsa <jolsa@redhat.com> - 2016-09-05 10:50 +0200
      Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Andi Kleen <andi@firstfloor.org> - 2016-09-05 18:30 +0200
      Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Kees Cook <keescook@chromium.org> - 2016-09-06 20:00 +0200
        Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-06 20:40 +0200
          Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Andi Kleen <andi@firstfloor.org> - 2016-09-06 21:50 +0200
            Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-06 21:50 +0200
              Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Kees Cook <keescook@chromium.org> - 2016-09-07 19:20 +0200
                Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-07 19:30 +0200
        Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Jiri Olsa <jolsa@redhat.com> - 2016-09-07 09:40 +0200
          Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Andi Kleen <andi@firstfloor.org> - 2016-09-07 18:40 +0200
            Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-07 19:00 +0200
              Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Jiri Olsa <jolsa@redhat.com> - 2016-09-07 21:30 +0200
                Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Jiri Olsa <jolsa@redhat.com> - 2016-09-07 23:30 +0200
                Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened  usercopy feature Linus Torvalds <torvalds@linux-foundation.org> - 2016-09-08 01:00 +0200

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