linux-kernel - Re: Userspace regression in LTS and stable kernels

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Date:   Fri, 15 Feb 2019 08:00:22 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     stable@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Richard Weinberger <richard.weinberger@...il.com>,
        Samuel Dionne-Riel <samuel@...nne-riel.com>,
        LKML <linux-kernel@...r.kernel.org>, graham@...hamc.com,
        Oleg Nesterov <oleg@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: Userspace regression in LTS and stable kernels

On Thu, Feb 14, 2019 at 12:20:27PM -0800, Andrew Morton wrote:
> On Thu, 14 Feb 2019 09:56:46 -0800 Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > On Wed, Feb 13, 2019 at 3:37 PM Richard Weinberger
> > <richard.weinberger@...il.com> wrote:
> > >
> > > Your shebang line exceeds BINPRM_BUF_SIZE.
> > > Before the said commit the kernel silently truncated the shebang line
> > > (and corrupted it),
> > > now it tells the user that the line is too long.
> > 
> > It doesn't matter if it "corrupted" things by truncating it. All that
> > matters is "it used to work, now it doesn't"
> > 
> > Yes, maybe it never *should* have worked. And yes, it's sad that
> > people apparently had cases that depended on this odd behavior, but
> > there we are.
> > 
> > I see that Kees has a patch to fix it up.
> > 
> 
> Greg, I think we have a problem here.
> 
> 8099b047ecc431518 ("exec: load_script: don't blindly truncate shebang
> string") wasn't marked for backporting.  And, presumably as a
> consequence, Kees's fix "exec: load_script: allow interpreter argument
> truncation" was not marked for backporting.
> 
> 8099b047ecc431518 hasn't even appeared in a Linus released kernel, yet
> it is now present in 4.9.x, 4.14.x, 4.19.x and 4.20.x.

It came in 5.0-rc1, so it fits the "in a Linus released kernel"
requirement.  If we are to wait until it shows up in a -final, that
would be months too late for almost all of these types of patches that
are picked up.

> I don't know if Oleg considered backporting that patch.  I certainly
> did (I always do), and I decided against doing so.  Yet there it is.

This came in through Sasha's tools, which give people a week or so to
say "hey, this isn't a stable patch!" and it seems everyone ignored that
:(

Where is Kees's fix?  I'll be glad to queue it up, or just revert the
above commit, which ever people think is easiest.

thanks,

greg k-h