On Mon, Nov 27, 2017 at 08:51:37AM -0500, Scott Mayhew wrote: > On Tue, 21 Nov 2017, Alexander Hermes wrote: > > > > Folks, > > > > > > I'm looking for some guidance on how to troubleshoot/debug an issue with (SELinux) labels over NFS that we've been having as a result of a kernel upgrade - description below. > > > I looked around on http://linux-nfs.org but was not able to find how to debug this kind of issue with labels - everything I found relates to more fundamental issues like mounts plain not working. > > > > > > With apologies for sending this to the devel mailing list, could you please help me get to the bottom of this? Or redirect me to somewhere / someone that can? > > > > > > Thank you very much, > > > > > > Alexander Hermes > > > > > > ---- > > > > > > ## Summary > > > > > > In upgrading our servers from CentOS 7.3 to 7.4 we upgraded the kernel from 3.10.0-327.36.2.el7.x86_64 to 3.10.0-693.2.2.el7.x86_64. As a result, NFS v4.2 mounts mounted via /etc/fstab at boot do not have proper SElinux label support - attempting to change labels on a mounted file leads to "Operation Not Supported". `ls -lZ` shows the incorrect labels. Upon rebooting to the earlier kernel version the issue goes away. > > > > > > ## Background > > > > > > As part of our gitlab HA deployment we use NFS to host data on a back end server that is then mounted by application servers (cf. https://docs.gitlab.com/ce/administration/high_availability/nfs.html). To do this we have a fairly typical setup where the server (in this example "enfigitback2-devel") exports a bunch of mounts via /etc/exports which are then mounted on a couple of application servers ("enfigitfront1-devel" / "enfigitfront2-devel"). > > > > > > ## The issue > > > > > > On the new kernel I am not able to change or view the SELinux labels of files / directories mounted on the client: > > > > > > ``` > > > [root@enfigitfront2-devel ~]# chcon --recursive --type ssh_home_t > > > /var/opt/gitlab/.ssh/authorized_keys > > > chcon: failed to change context of > > > '/var/opt/gitlab/.ssh/authorized_keys' to > > > 'system_u:object_r:ssh_home_t:s0': Operation not supported > > > [root@enfigitfront2-devel ~]# uname -r > > > 3.10.0-693.2.2.el7.x86_64 > > > ``` > > > On the old kernel I am: > > > > > > ``` > > > [root@enfigitfront1-devel ~]# chcon --recursive --type ssh_home_t > > > /var/opt/gitlab/.ssh/authorized_keys > > > [root@enfigitfront1-devel ~]# uname -r > > > 3.10.0-327.36.2.el7.x86_64 > > > ``` > > > > > > We can't keep using the old kernel forever so I'd like to get to the bottom of this - what could this be due to? How can I debug this further to understand where the "Operation not supported" is coming from? > > > > > > ## Server details > > > Distro: CentOS 7.3 / 7.4 > > > Kernel (`uname -r`): > > > * 3.10.0-514.10.2.el7.x86_64 (server) > > > * 3.10.0-693.2.2.el7.x86_64 (client - new) > > > * 3.10.0-327.36.2.el7.x86_64 (client - old) > > > nfs-utils: RPM package version 1.3.0 > > > > > > > > > Server mount option example: > > > /export/.ssh 172.18.10.148(rw,sync,no_root_squash) > > > 172.18.10.151(rw,sync,no_root_squash) > > > > Add "security_label" to the export options above. If you don't see "security_label" listed in the exports(5) man page then you need to upgrade your nfs-utils package. > > > > -Scott > > > > > > > > Client mount options (/etc/fstab): > > > enfigitback2-devel.datcon.co.uk:/export/.ssh /var/opt/gitlab/.ssh nfs defaults,soft,v4.2,rsize=1048576,wsize=1048576,noatime,_netdev,lookupcache=none 0 0 > > > > > > ## Debugging I've done > > > > > > ### Mounting by hand > > > I tried to mount one of the exported mounts "by hand" using `mount` and found the following: > > > * mounting the same export on a different mount point using the same > > > options as in /etc/fstab yields a mount that has the same issue > > > * mounting with `nosharecache` results in a mount that *does not* have the issue. > > > > > > > > > > > > Hi Scott, > > > > Thank you for pointing out "security_label". I have applied the option... > > > > /export/.ssh 172.18.10.148(rw,sync,no_root_squash,security_label) 172.18.10.151(rw,sync,no_root_squash,security_label) > > > > and rebooted both server and client (in that order), but I still see the same behaviour as before on the server with the uplevel kernel: > > > > [root@enfigitfront2-devel ~]# chcon --recursive --type ssh_home_t /var/opt/gitlab/.ssh/authorized_keys > > chcon: failed to change context of '/var/opt/gitlab/.ssh/authorized_keys' to 'system_u:object_r:ssh_home_t:s0': Operation not supported > > > > I notice that the exports(5) man page mentions " This will only work if all clients use a consistent security policy." under security_label. I'm not sure what a "consistent security policy" means - what does this mean in terms of options/configuration? > > I'm assuming that means you don't want some clients using full labeled > NFS, others mounting with the context= mount option, and others with > SELinux completely disabled. With labeled NFS, the creation and > enforcement of labels happens on the client side and the server just > stores the labels. So also for example if the clients disagree about how to label files in your home directory, or something, then things will likely break. I don't know how big a problem that is in practice. --b. > > Anyways, I missed the fact that your clients are using an earlier > kernel. In order to get the desired behavior when mounting an NFS > server that is using the "security_label" export option, you're pretty > much going to need to run an updated kernel on the clients too... > specifically one with commit 0b4d3452b "security/selinux: allow > security_sb_clone_mnt_opts to enable/disable native labeling behavior". > AFAIK CentOS 7.4 should have it (because RHEL 7.4 has it). > > -Scott > > > > > > Thanks for the help, > > Alex > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
