netdev - Re: [PATCH] lsm: make security_socket_getpeersec_stream() sockptr

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Message-ID: <8781116e-1738-5cbf-976c-328ebeafba67@canonical.com>
Date:   Fri, 28 Oct 2022 05:31:20 -0700
From:   John Johansen <john.johansen@...onical.com>
To:     Paul Moore <paul@...l-moore.com>,
        Casey Schaufler <casey@...aufler-ca.com>
Cc:     netdev@...r.kernel.org,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org
Subject: Re: [PATCH] lsm: make security_socket_getpeersec_stream() sockptr_t
 safe

On 10/10/22 15:00, Paul Moore wrote:
> On Mon, Oct 10, 2022 at 5:58 PM Paul Moore <paul@...l-moore.com> wrote:
>>
>> Commit 4ff09db1b79b ("bpf: net: Change sk_getsockopt() to take the
>> sockptr_t argument") made it possible to call sk_getsockopt()
>> with both user and kernel address space buffers through the use of
>> the sockptr_t type.  Unfortunately at the time of conversion the
>> security_socket_getpeersec_stream() LSM hook was written to only
>> accept userspace buffers, and in a desire to avoid having to change
>> the LSM hook the commit author simply passed the sockptr_t's
>> userspace buffer pointer.  Since the only sk_getsockopt() callers
>> at the time of conversion which used kernel sockptr_t buffers did
>> not allow SO_PEERSEC, and hence the
>> security_socket_getpeersec_stream() hook, this was acceptable but
>> also very fragile as future changes presented the possibility of
>> silently passing kernel space pointers to the LSM hook.
>>
>> There are several ways to protect against this, including careful
>> code review of future commits, but since relying on code review to
>> catch bugs is a recipe for disaster and the upstream eBPF maintainer
>> is "strongly against defensive programming", this patch updates the
>> LSM hook, and all of the implementations to support sockptr_t and
>> safely handle both user and kernel space buffers.
>>
>> Signed-off-by: Paul Moore <paul@...l-moore.com>
>> ---
>>   include/linux/lsm_hook_defs.h |    2 +-
>>   include/linux/lsm_hooks.h     |    4 ++--
>>   include/linux/security.h      |   11 +++++++----
>>   net/core/sock.c               |    3 ++-
>>   security/apparmor/lsm.c       |   29 +++++++++++++----------------
>>   security/security.c           |    6 +++---
>>   security/selinux/hooks.c      |   13 ++++++-------
>>   security/smack/smack_lsm.c    |   19 ++++++++++---------
>>   8 files changed, 44 insertions(+), 43 deletions(-)
> 
> Casey and John, could you please look over the Smack and AppArmor bits
> of this patch when you get a chance?  I did my best on the conversion,
> but I would appreciate a review by the experts :)
> 
yes, I plan to look at it this weekend