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Mon, 3 Jan 2022 14:09:38 +0000 (GMT) Received: from [9.47.158.152] (unknown [9.47.158.152]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP; Mon, 3 Jan 2022 14:09:38 +0000 (GMT) Message-ID: <0626de21-d22f-329c-fc64-ecd7eab1331a@linux.ibm.com> Date: Mon, 3 Jan 2022 09:09:37 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH v7 10/14] securityfs: Extend securityfs with namespacing support Content-Language: en-US To: Christian Brauner , Stefan Berger Cc: linux-integrity@vger.kernel.org, zohar@linux.ibm.com, serge@hallyn.com, containers@lists.linux.dev, dmitry.kasatkin@gmail.com, ebiederm@xmission.com, krzysztof.struczynski@huawei.com, roberto.sassu@huawei.com, mpeters@redhat.com, lhinds@redhat.com, lsturman@redhat.com, puiterwi@redhat.com, jejb@linux.ibm.com, jamjoom@us.ibm.com, linux-kernel@vger.kernel.org, paul@paul-moore.com, rgb@redhat.com, linux-security-module@vger.kernel.org, jmorris@namei.org, James Bottomley References: <20211216054323.1707384-1-stefanb@linux.vnet.ibm.com> <20211216054323.1707384-11-stefanb@linux.vnet.ibm.com> <20211216134027.33sprdmhol2tbctf@wittgenstein> From: Stefan Berger In-Reply-To: <20211216134027.33sprdmhol2tbctf@wittgenstein> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: jsA1Gn0Zs6K0t0IbxU9x7rtF5PCW93Ws X-Proofpoint-ORIG-GUID: uXiAfUfvBh1c5O8bgcGxgWWeD9yraZ7d X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.790,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2022-01-03_05,2022-01-01_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 mlxscore=0 suspectscore=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 phishscore=0 adultscore=0 spamscore=0 clxscore=1015 impostorscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2110150000 definitions=main-2201030096 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/16/21 08:40, Christian Brauner wrote: > On Thu, Dec 16, 2021 at 12:43:19AM -0500, Stefan Berger wrote: >> From: Stefan Berger >> >> Extend 'securityfs' for support of IMA namespacing so that each >> IMA (user) namespace can have its own front-end for showing the currently >> active policy, the measurement list, number of violations and so on. >> >> Drop the addition dentry reference to enable simple cleanup of dentries >> upon umount. >> >> Prevent mounting of an instance of securityfs in another user namespace >> than it belongs to. Also, prevent accesses to directories when another >> user namespace is active than the one that the instance of securityfs >> belongs to. >> >> Signed-off-by: Stefan Berger >> Signed-off-by: James Bottomley >> --- >> security/inode.c | 37 ++++++++++++++++++++++++++++++++++--- >> 1 file changed, 34 insertions(+), 3 deletions(-) >> >> diff --git a/security/inode.c b/security/inode.c >> index fee01ff4d831..a0d9f086e3d5 100644 >> --- a/security/inode.c >> +++ b/security/inode.c >> @@ -26,6 +26,29 @@ >> static struct vfsmount *init_securityfs_mount; >> static int init_securityfs_mount_count; >> >> +static int securityfs_permission(struct user_namespace *mnt_userns, >> + struct inode *inode, int mask) >> +{ >> + int err; >> + >> + err = generic_permission(&init_user_ns, inode, mask); >> + if (!err) { >> + if (inode->i_sb->s_user_ns != current_user_ns()) >> + err = -EACCES; > I really think the correct semantics is to grant all callers access > whose user namespace is the same as or an ancestor of the securityfs > userns. It's weird to deny access to callers who are located in an > ancestor userns. Ok, will be using current_in_userns() or the more explicit in_userns() for the check. > > For example, a privileged process on the host should be allowed to setns > to the userns of an unprivileged container and inspect its securityfs > instance. > > We're mostly interested to block such as scenarios where two sibling > unprivileged containers are created in the initial userns and an fd > proxy or something funnels a file descriptor from one sibling container > to the another one and the receiving sibling container can use readdir() > or openat() on this fd. (I'm not even convinced that this is actually a > problem but stricter semantics at the beginning can't hurt. We can > always relax this later.)