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Date:   Thu, 14 Feb 2019 12:20:27 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Richard Weinberger <richard.weinberger@gmail.com>,
        Samuel Dionne-Riel <samuel@dionne-riel.com>,
        LKML <linux-kernel@vger.kernel.org>, graham@grahamc.com,
        Oleg Nesterov <oleg@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        Michal Hocko <mhocko@suse.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: Userspace regression in LTS and stable kernels
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On Thu, 14 Feb 2019 09:56:46 -0800 Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Wed, Feb 13, 2019 at 3:37 PM Richard Weinberger
> <richard.weinberger@gmail.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.

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.