Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Andrew Morton]

On Thu, 29 Mar 2012 15:01:46 -0500
Will Drewry <wad-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> wrote:

> From: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
> 
> With this set, a lot of dangerous operations (chroot, unshare, etc)
> become a lot less dangerous because there is no possibility of
> subverting privileged binaries.

The changelog doesn't explain the semantics of the new syscall. 
There's a comment way-down-there which I guess suffices, if you hunt
for it.

And the changelog doesn't explain why this is being added.  Presumably
seccomp_filter wants/needs this feature but whowhatwherewhenwhy?  Spell
it all out, please.

The new syscall mode will be documented in the prctl manpage.  Please
cc linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org and work with Michael on getting this
done?

>
> ...
>
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Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Andrew Lutomirski]

On Fri, Apr 6, 2012 at 12:55 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Thu, 29 Mar 2012 15:01:46 -0500
> Will Drewry <wad@chromium.org> wrote:
>
>> From: Andy Lutomirski <luto@amacapital.net>
>>
>> With this set, a lot of dangerous operations (chroot, unshare, etc)
>> become a lot less dangerous because there is no possibility of
>> subverting privileged binaries.
>
> The changelog doesn't explain the semantics of the new syscall.
> There's a comment way-down-there which I guess suffices, if you hunt
> for it.
>
> And the changelog doesn't explain why this is being added.  Presumably
> seccomp_filter wants/needs this feature but whowhatwherewhenwhy?  Spell
> it all out, please.
>
> The new syscall mode will be documented in the prctl manpage.  Please
> cc linux-man@vger.kernel.org and work with Michael on getting this
> done?

This has been bugging me for awhile.  Is there any interest in moving
the manpages into the kernel source tree?  Then there could be a
general requirement that new APIs get documented when they're written.

(There are plenty of barely- or incompletely-documented syscalls.
futex and relatives come to mind.)

--Andy

Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Jonathan Corbet]

On Fri, 6 Apr 2012 13:01:17 -0700
Andrew Lutomirski <luto@mit.edu> wrote:

> This has been bugging me for awhile.  Is there any interest in moving
> the manpages into the kernel source tree?  Then there could be a
> general requirement that new APIs get documented when they're written.

Man page (or other documentation) requirements for patch acceptance are a
regular kernel summit feature.  People seem to think it's a good idea, but
actual enforcement of such requirements always seems to be lacking.  Lots
of people have kind of given up trying.  I don't really see that adding
the man pages to the tree would help, but I could be wrong...

jon

Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Andrew Lutomirski]

On Fri, Apr 6, 2012 at 1:28 PM, Jonathan Corbet <corbet@lwn.net> wrote:
> On Fri, 6 Apr 2012 13:01:17 -0700
> Andrew Lutomirski <luto@mit.edu> wrote:
>
>> This has been bugging me for awhile.  Is there any interest in moving
>> the manpages into the kernel source tree?  Then there could be a
>> general requirement that new APIs get documented when they're written.
>
> Man page (or other documentation) requirements for patch acceptance are a
> regular kernel summit feature.  People seem to think it's a good idea, but
> actual enforcement of such requirements always seems to be lacking.  Lots
> of people have kind of given up trying.  I don't really see that adding
> the man pages to the tree would help, but I could be wrong...
>

If it's in the source, then I can send it with git format-patch.  If
it's out of tree, I have to find the tree, clone the tree, figure out
how to submit, and send separate emails.  And then whoever checks that
I documented it has to figure out where I sent it and how to read it
and then try to decide which documentation submission matches which
patch submission.

(Also, if it's in-tree, then I can build the docs from a kernel tree
and have the latest ones.  That could be nice.)

--Andy

Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Michael Kerrisk (man-pages)]

On Sat, Apr 7, 2012 at 8:28 AM, Jonathan Corbet <corbet@lwn.net> wrote:
> On Fri, 6 Apr 2012 13:01:17 -0700
> Andrew Lutomirski <luto@mit.edu> wrote:
>
>> This has been bugging me for awhile.  Is there any interest in moving
>> the manpages into the kernel source tree?  Then there could be a
>> general requirement that new APIs get documented when they're written.
>
> Man page (or other documentation) requirements for patch acceptance are a
> regular kernel summit feature.  People seem to think it's a good idea, but
> actual enforcement of such requirements always seems to be lacking.  Lots
> of people have kind of given up trying.  I don't really see that adding
> the man pages to the tree would help, but I could be wrong...

I largely consider this (moving man pages to kernel.org) a technical
solution to what is fundamentally a social problem (developers
reluctant to write documentation), and doubt that the technical
solution would make much difference. I'd love to be proved wrong, but
the experiment would require significant start-up effort. (My
collected thoughts on this can be found here:
http://www.kernel.org/doc/man-pages/todo.html#migrate_to_kernel_source.
Note the alternative idea of patch tags mentioned at the end of that
text.)

Unless, or until there's a paid maintainer, I don't expect things to
get significantly better than what they currently are. The quite
significant improvements in man-pages since 2004, when I became
maintainer were in small part due to the fact that I was for a short
period paid to do the work, but in much larger part due to a huge
private effort over those years which over the last couple of years is
no longer unsustainable for me (man-pages is in competition with
requirements for my attention from family, working life, and
(seriously!) seismic events),

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/

Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Michael Kerrisk (man-pages)]

> no longer unsustainable for me (man-pages is in competition with

^no longer unsustainable^no longer sustainable

Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Andrew Lutomirski]

On Wed, Apr 11, 2012 at 12:31 PM, Michael Kerrisk (man-pages)
<mtk.manpages@gmail.com> wrote:
> On Sat, Apr 7, 2012 at 8:28 AM, Jonathan Corbet <corbet@lwn.net> wrote:
>> On Fri, 6 Apr 2012 13:01:17 -0700
>> Andrew Lutomirski <luto@mit.edu> wrote:
>>
>>> This has been bugging me for awhile.  Is there any interest in moving
>>> the manpages into the kernel source tree?  Then there could be a
>>> general requirement that new APIs get documented when they're written.
>>
>> Man page (or other documentation) requirements for patch acceptance are a
>> regular kernel summit feature.  People seem to think it's a good idea, but
>> actual enforcement of such requirements always seems to be lacking.  Lots
>> of people have kind of given up trying.  I don't really see that adding
>> the man pages to the tree would help, but I could be wrong...
>
> I largely consider this (moving man pages to kernel.org) a technical
> solution to what is fundamentally a social problem (developers
> reluctant to write documentation), and doubt that the technical
> solution would make much difference. I'd love to be proved wrong, but
> the experiment would require significant start-up effort. (My
> collected thoughts on this can be found here:
> http://www.kernel.org/doc/man-pages/todo.html#migrate_to_kernel_source.
> Note the alternative idea of patch tags mentioned at the end of that
> text.)
>
> Unless, or until there's a paid maintainer, I don't expect things to
> get significantly better than what they currently are. The quite
> significant improvements in man-pages since 2004, when I became
> maintainer were in small part due to the fact that I was for a short
> period paid to do the work, but in much larger part due to a huge
> private effort over those years which over the last couple of years is
> no longer unsustainable for me (man-pages is in competition with
> requirements for my attention from family, working life, and
> (seriously!) seismic events),

Hrm.  Maybe someone could convince Andrew and Linus not to pull new
syscalls or major ABI features unless the patchset includes full docs.

Anyway, I'll write up a detailed description of PR_SET_NO_NEW_PRIVS,
stick it in the changelog, and cc linux-doc.

--Andy

Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Rob Landley]

On 04/11/2012 02:31 PM, Michael Kerrisk (man-pages) wrote:
> On Sat, Apr 7, 2012 at 8:28 AM, Jonathan Corbet <corbet@lwn.net> wrote:
>> On Fri, 6 Apr 2012 13:01:17 -0700
>> Andrew Lutomirski <luto@mit.edu> wrote:
>>
>>> This has been bugging me for awhile.  Is there any interest in moving
>>> the manpages into the kernel source tree?  Then there could be a
>>> general requirement that new APIs get documented when they're written.
>>
>> Man page (or other documentation) requirements for patch acceptance are a
>> regular kernel summit feature.  People seem to think it's a good idea, but
>> actual enforcement of such requirements always seems to be lacking.  Lots
>> of people have kind of given up trying.  I don't really see that adding
>> the man pages to the tree would help, but I could be wrong...
> 
> I largely consider this (moving man pages to kernel.org) a technical
> solution to what is fundamentally a social problem (developers
> reluctant to write documentation), and doubt that the technical
> solution would make much difference.

*nod* *nod*

> I'd love to be proved wrong, but
> the experiment would require significant start-up effort. (My
> collected thoughts on this can be found here:
> http://www.kernel.org/doc/man-pages/todo.html#migrate_to_kernel_source.
> Note the alternative idea of patch tags mentioned at the end of that
> text.)
> 
> Unless, or until there's a paid maintainer, I don't expect things to
> get significantly better than what they currently are.

Maintainer of which, the man pages or the kernel Documentation directory?

I just got handed the Documentation ball (right as relatives were
visiting and a couple days before buying a new house, so I've just put
_tons_ of time into it so far). I have grandiose plans for cleaning it
up, but first I need to get my kernel.org account working again.

That said, I think having man-pages in the kernel directory is a bad
idea, for reasons I already posted to this thread.

> The quite
> significant improvements in man-pages since 2004, when I became
> maintainer were in small part due to the fact that I was for a short
> period paid to do the work, but in much larger part due to a huge
> private effort over those years which over the last couple of years is
> no longer unsustainable for me (man-pages is in competition with
> requirements for my attention from family, working life, and
> (seriously!) seismic events),

Heh, I know the feeling. :)

Circa 2007 I was paid to work on documentation for half a year (hence
the http://kernel.org/doc directory I stopped being able to update when
kernel.org got hacked). These days it competes with my toybox and
aboriginal linux projects, and with my day job.

The way I'm looking at it is I'm _curating_ documentation.  I'm acting
as some kind of of librarian, and my first goal is reshuffling the files
in Documentation into some semblance of order so you can see what's
there.  (I've posted about that before here, moving
architecture-specific stuff under an arch subdirectory and so on.)

I do sometimes write new documentation, but no human being knows
everything there is to know about the kernel. Building expertise is
enormously time consuming,

That said, if anything was going to move into the kernel moving the
syscall info into javadoc might make sense.

Something that might help you is the syscall mining script snippet I
posted last time:

find . -name "*.c" -print0 | \
xargs -n1 -0 sed -n -e 's/.*\(SYSCALL_DEFINE[0-9](\)/\1/' \
  -e 't got;d;:got;s/).*/)/p;t;N;b got'

I might be able to build a script around that which would look up the
system call number, figure out which architectures implement this call,
find any javadoc at the call site, and so on. That way we could automate
this a bit.  For example, kernel/fork.c has two syscalls:

SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)

/*
 * unshare allows a process to 'unshare' part of the process
 * context which was originally shared using clone.  copy_*
 * functions used by do_fork() cannot be used here directly
 * because they modify an inactive task_struct that is being
 * constructed. Here we are modifying the current, active,
 * task_struct.
 */
SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)

Both of these have man pages which provide way more info than the
comments (if any). Is there any sort of javadoc comment before the
syscall that might provide useful information you could automatically
harvest?  Some sort of standard header briefly defining the syscall?

(P.S. Speaking of man 2 unshare, what's with the #define _GNU_SOURCE for
a new linux kernel syscall? What the heck does the FSF have to do with
anything? This didn't used to be needed in ubuntu 10.04 but then the
headers changed to match the man page, which I found sad...)

> Cheers,
> 
> Michael

Rob
-- 
GNU/Linux isn't: Linux=GPLv2, GNU=GPLv3+, they can't share code.
Either it's "mere aggregation", or a license violation.  Pick one.

Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Rob Landley]

On 04/06/2012 03:01 PM, Andrew Lutomirski wrote:
> On Fri, Apr 6, 2012 at 12:55 PM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
>> On Thu, 29 Mar 2012 15:01:46 -0500
>> Will Drewry <wad@chromium.org> wrote:
>>
>>> From: Andy Lutomirski <luto@amacapital.net>
>>>
>>> With this set, a lot of dangerous operations (chroot, unshare, etc)
>>> become a lot less dangerous because there is no possibility of
>>> subverting privileged binaries.
>>
>> The changelog doesn't explain the semantics of the new syscall.
>> There's a comment way-down-there which I guess suffices, if you hunt
>> for it.
>>
>> And the changelog doesn't explain why this is being added.  Presumably
>> seccomp_filter wants/needs this feature but whowhatwherewhenwhy?  Spell
>> it all out, please.
>>
>> The new syscall mode will be documented in the prctl manpage.  Please
>> cc linux-man@vger.kernel.org and work with Michael on getting this
>> done?
> 
> This has been bugging me for awhile.  Is there any interest in moving
> the manpages into the kernel source tree?

Not that I know of. I'm pretty sure if the guy maintaining it (Michael
Kerrisk) wanted to do that, he could have raised the issue at any time
over the past several years.

> Then there could be a
> general requirement that new APIs get documented when they're written.

Because having a Documentation directory, javadoc in the source itself
(some of which is combined with the Documentation/DocBook xml files to
form the make htmldocs output), menuconfig help text, and a whole buch
of scattered readmes does _not_ get new APIs documented as they're written.

That isn't even counting git commit comments and mailing list messages
in various web archives. Are you going to suck the linux weekly news
kernel articles into the tree (http://lwn.net/Kernel/Index)? How about
Linux Journal's complete archives going back to 2004
(http://www.linuxjournal.com/magazine)? Or the h-online and
kernelnewbies writeups? How about wikipedia pages on interesting kernel
topics? The sourceforge pages for userspace projects like lxc.sf.net or
i2c-utils? How about that device driver writing tutorial Greg KH
recorded in 2008, that's only a 2.8 gigabyte video file.  Rusty's
Unreliable Guides?  Greg KH's blog? (Heck, http://kernelplanet.org).

Speaking of videos, here's the 2011 LinuxCon Japan talks:

  http://video.linux.com/categories/2011-linuxcon-japan

And here are videos for the Consumer Electronic Linux Forum:

  http://free-electrons.com/blog/elc-2012-videos/

(and you can get 2011, 2010, 2006...)

Here are Ottawa Linux Symposium papers:

  http://kernel.org/doc/ols

Don't forget IBM Developerworks' library:

http://www.ibm.com/developerworks/linux/library/l-linux-kernel/

Have some standards documents:

http://www.opengroup.org/onlinepubs/9699919799/
http://busybox.net/~landley/c99-draft.html
http://www.unix.org/whitepapers/64bit.html
http://refspecs.linuxfoundation.org
http://t10.org/scsi-3.htm

Here's a random blog post about booting a bare metal "hello world"
program on qemu for ARM:

http://balau82.wordpress.com/2010/02/28/hello-world-for-bare-metal-arm-using-qemu/

Let's pick a topic, like the ELF loader. Here's the best introduction of
how ELF files _really_ work I've seen:

http://muppetlabs.com/~breadbox/software/tiny/teensy.html

Although http://linuxjournal.com/article/1059 is pretty good too, as
were http://linuxjournal.com/article/1060 and
http://linuxjournal.com/article/80 as well.  And if you want the
_details_, here's an extremely dry online book:

http;//www.iecc.com/linker/

And here's the first entry in the blog series the guy who wrote "gold"
did about writing his new linker:

http://www.airs.com/blog/archives/38

And so on, and so forth...

> (There are plenty of barely- or incompletely-documented syscalls.
> futex and relatives come to mind.)

Your proposal does not address this problem.

speaking of syscalls, I do note that ever since I tried to add Hexagon
support to strace (less fun than it sounds), I've wanted a way to beat
proper syscall information out of the kernel headers so I could get not
just syscall numbers but how many arguments and a brief stab at the type
of each argument.

Of course you _can_ get argument type and count, but not from the
headers: you have to use moderately horrible sed on the kernel's source
code, ala:

find . -name "*.c" -print0 | \
xargs -n1 -0 sed -n -e 's/.*\(SYSCALL_DEFINE[0-9](\)/\1/' \
  -e 't got;d;:got;s/).*/)/p;t;N;b got'

> --Andy

Rob
-- 
GNU/Linux isn't: Linux=GPLv2, GNU=GPLv3+, they can't share code.
Either it's "mere aggregation", or a license violation.  Pick one.

Re: [PATCH v17 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

[Will Drewry]

On Fri, Apr 6, 2012 at 2:55 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> On Thu, 29 Mar 2012 15:01:46 -0500
> Will Drewry <wad@chromium.org> wrote:
>
>> From: Andy Lutomirski <luto@amacapital.net>
>>
>> With this set, a lot of dangerous operations (chroot, unshare, etc)
>> become a lot less dangerous because there is no possibility of
>> subverting privileged binaries.
>
> The changelog doesn't explain the semantics of the new syscall.
> There's a comment way-down-there which I guess suffices, if you hunt
> for it.

I'll bubble up luto's comment into the changelog when I resend the
grand-unified-patchset.

> And the changelog doesn't explain why this is being added.  Presumably
> seccomp_filter wants/needs this feature but whowhatwherewhenwhy?  Spell
> it all out, please.

I'll try my hand at that and luto@ can yell at me if I misrepresent.
Seem reasonable?

> The new syscall mode will be documented in the prctl manpage.  Please
> cc linux-man@vger.kernel.org and work with Michael on getting this
> done?

I'll add linux-man to the patch series since this applies to both
no_new_privs and seccomp filter.

Thanks!

>>
>> ...
>>