linux-kernel - Re: [Jfs-discussion] [PATCH] jfs: Expand usercopy whitelist for inline inode data

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Message-ID: <alpine.DEB.2.21.999.1808200032460.791@trent.utfs.org>
Date:   Mon, 20 Aug 2018 00:36:37 -0700 (PDT)
From:   Christian Kujau <lists@...dbynature.de>
To:     Kees Cook <keescook@...omium.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Bart Massey <bart.massey@...il.com>,
        jfs-discussion@...ts.sourceforge.net,
        David Windsor <dave@...lcore.net>,
        Dave Kleikamp <shaggy@...nel.org>,
        Ben Hutchings <ben@...adent.org.uk>
Subject: Re: [Jfs-discussion] [PATCH] jfs: Expand usercopy whitelist for
 inline inode data

On Fri, 17 Aug 2018, Kees Cook wrote:
> On Thu, Aug 16, 2018 at 11:56 PM, Christian Kujau <lists@...dbynature.de> wrote:
> > On Fri, 3 Aug 2018, Kees Cook via Jfs-discussion wrote:
> >> Bart Massey reported what turned out to be a usercopy whitelist false
> >> positive in JFS when symlink contents exceeded 128 bytes. The inline
> >> inode data (i_inline) is actually designed to overflow into the "extended
> >
> > So, this may be a stupid question, but: is there a way to disable this
> > hardened usercopy thing with a boot option maybe?
> >
> > Apparently, CONFIG_HARDENED_USERCOPY_FALLBACK was disabled in Debian's
> > 4.16.0-0.bpo.2-amd64 (4.16.16) kernels[0] and I have a VMware guest here
> > that prints a BUG message (below) whenever a certain directory is being
> > accesses. ls(1) is fine, but "ls -l" (i.e. with stat()) produces the splat
> > below. And indeed, the target of one of the symlinks inside is 129
> > characters long, and every attempt to stat it prints the splat below.
> >
> > Going back to 4.16.0-0.bpo.1-amd64 (4.16.5) helps, but I was wondering if
> > there was a magic boot option to disable it while I wait for 4.18 to land
> > in Debian? I booted with hardened_usercopy=off, but it doesn't seem to
> > have an effect and the directory is still inaccessible.
> 
> Precisely this was just added upstream[1] for 4.19 but isn't available
> in 4.16. It should be trivial to backport it, though, if Ben wants to
> do that? (The JFS fix is in the 4.17 and 4.18 -stable trees now, too,
> BTW.)

Ah, OK. While the patch does apply (almost) cleanly to 4.16, I think I'll 
just wait until it makes its way into the Debian (backports) kernel, as 
nobody else seems to be annoyed by this :-)

Thanks!
Christian.
-- 
BOFH excuse #53:

Little hamster in running wheel had coronary; waiting for replacement to be Fedexed from Wyoming