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From:   Piotr Sawicki <p.sawicki2@partner.samsung.com>
Subject: Re: [PATCH v1 20/22] Move common usercopy into
 security_getpeersec_stream
To:     Casey Schaufler <casey@schaufler-ca.com>,
        LSM <linux-security-module@vger.kernel.org>,
        LKLM <linux-kernel@vger.kernel.org>,
        Paul Moore <paul@paul-moore.com>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        SE Linux <selinux@tycho.nsa.gov>,
        "SMACK-discuss@lists.01.org" <SMACK-discuss@lists.01.org>,
        John Johansen <john.johansen@canonical.com>,
        Kees Cook <keescook@chromium.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        James Morris <jmorris@namei.org>
Cc:     "Schaufler, Casey" <casey.schaufler@intel.com>
Newsgroups: gmane.linux.kernel,gmane.linux.kernel.lsm,gmane.comp.security.selinux
Date:   Fri, 3 Aug 2018 11:10:09 +0200
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On 07/16/2018 08:24 PM, Casey Schaufler wrote:
> [PATCH 20/22] Move common usercopy into security_getpeersec_stream
> 
> The modules implementing hook for getpeersec_stream
> don't need to be duplicating the copy-to-user checks.
> Moving the user copy part into the infrastructure makes
> the security module code simpler and reduces the places
> where user copy code may go awry.

Hi,

This change will break the API. Some clients may call getsockopt(..,SO_PEERSEC,..) twice. Firstly, to fetch the length. In that case xxx_socket_getpeersec_stream should return -ERANGE and set *optlen. Secondly, to retrieve a proper security label.

Please take a look at the implementation of the getClientSmackLabel() function in Cynara: https://review.tizen.org/gerrit/#/c/26888/6/src/helpers/creds-socket/creds-socket-inner.cpp
Also there is an email thread about this socket option which tells us why it is made this way: "[RFC] SO_PEERSEC - security credentials for Unix stream sockets"

http://lists.jammed.com/linux-security-module/2003/12/0029.html

Regards,
Piotr