linux-kernel - [PATCH 0/1] userfaultfd: require CAP_SYS_PTRACE for UFFD_FEATURE_EVENT

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Date:   Tue,  5 Nov 2019 17:29:36 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Daniel Colascione <dancol@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Nick Kralevich <nnk@...gle.com>,
        Nosh Minwalla <nosh@...gle.com>,
        Pavel Emelyanov <ovzxemul@...il.com>,
        Tim Murray <timmurray@...gle.com>, linux-api@...r.kernel.org,
        linux-mm@...ck.org, Mike Rapoport <rppt@...ux.ibm.com>
Subject: [PATCH 0/1] userfaultfd: require CAP_SYS_PTRACE for UFFD_FEATURE_EVENT_FORK

Hi,

A while ago Andy noticed [1] that UFFD_FEATURE_EVENT_FORK used by an
unprivileged user may have security implications.

As the first step of the solution the following patch limits the
availably of UFFD_FEATURE_EVENT_FORK only for those having CAP_SYS_PTRACE.

The usage of CAP_SYS_PTRACE ensures compatibility with CRIU.

Yet, if there are other users of non-cooperative userfaultfd that run
without CAP_SYS_PTRACE, they would be broken :(

[1] https://lore.kernel.org/lkml/CALCETrWY+5ynDct7eU_nDUqx=okQvjm=Y5wJvA4ahBja=CQXGw@mail.gmail.com

Mike Rapoport (1):
  userfaultfd: require CAP_SYS_PTRACE for UFFD_FEATURE_EVENT_FORK

 fs/userfaultfd.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

-- 
2.7.4