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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Kees Cook <keescook@chromium.org>,
	regressions@lists.linux.dev,
	 Andrea Righi <andrea.righi@canonical.com>
Subject: Re: Regression when writing to /proc/<pid>/attr/
Date: Tue, 8 Jun 2021 09:39:03 -0700	[thread overview]
Message-ID: <CAHk-=wg93iejO6zMZpXTnszrjdr=-iKjuC4q_LsGtNsuhfTCHg@mail.gmail.com> (raw)
In-Reply-To: <20210608115928.5ocvtyoekxa2a6vw@wittgenstein>

On Tue, Jun 8, 2021 at 4:59 AM Christian Brauner
<christian.brauner@ubuntu.com> wrote:
>
> Hm, but doesn't the mm check have the same problem? It's not checking
> the mm of the opener against the mm of the writer. To stay with the
> example in this thread, it's checking the mm of the <attached process>
> at open time against the mm of the <attached process> at write time if I
> read this correctly.

Yes and no. It is checking that the mm of the target still matches,
but what you don't see in the patch (because it was pre-existing) is
that it also checks that the target is "current".

So it does effectively check that current hasn't execve'd. So ack on
the patch from me.

Of course, we could _also_ allow a cross-execve() write if the creds
remain the same, but I think this "hasn't execve'd" is the better
check (and was what the original cred check patch basically aimed to
do anyway).

           Linus

  reply	other threads:[~2021-06-08 16:39 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-07 14:22 Regression when writing to /proc/<pid>/attr/ Christian Brauner
2021-06-07 23:38 ` Kees Cook
2021-06-08  0:02   ` Linus Torvalds
2021-06-08  2:15     ` Kees Cook
2021-06-08  6:44       ` Andrea Righi
2021-06-08 17:03         ` Kees Cook
2021-06-08 11:59       ` Christian Brauner
2021-06-08 16:39         ` Linus Torvalds [this message]
2021-06-08  8:51   ` Christian Brauner

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