On Fri, Oct 9, 2020 at 12:36 PM Olga Kornievskaia <aglo@xxxxxxxxx> wrote: > > On Fri, Oct 9, 2020 at 10:08 AM Chuck Lever <chucklever@xxxxxxxxx> wrote: > > > > > > > > > On Oct 9, 2020, at 7:49 AM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote: > > > > > > On Thu, Oct 8, 2020 at 9:03 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote: > > >> > > >> ->On Thu, Oct 8, 2020 at 9:50 AM Olga Kornievskaia <aglo@xxxxxxxxx> wrote: > > >>> On Wed, Oct 7, 2020 at 9:07 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote: > > >>>> On Wed, Oct 7, 2020 at 8:41 PM Olga Kornievskaia <aglo@xxxxxxxxx> wrote: > > >>>>> Hi folks, > > >>>>> > > >>>>> From some linux kernel module, is it possible to query and find out > > >>>>> whether or not selinux is currently enabled or not? > > >>>>> > > >>>>> Thank you. > > >>>> > > >>>> [NOTE: CC'ing the SELinux list as it's probably a bit more relevant > > >>>> that the LSM list] > > >>>> > > >>>> In general most parts of the kernel shouldn't need to worry about what > > >>>> LSMs are active and/or enabled; the simply interact with the LSM(s) > > >>>> via the interfaces defined in include/linux/security.h (there are some > > >>>> helpful comments in include/linux/lsm_hooks.h). Can you elaborate a > > >>>> bit more on what you are trying to accomplish? > > >>> > > >>> Hi Paul, > > >>> > > >>> Thank you for the response. What I'm trying to accomplish is the > > >>> following. Within a file system (NFS), typically any queries for > > >>> security labels are triggered by the SElinux (or I guess an LSM in > > >>> general) (thru the xattr_handler hooks). However, when the VFS is > > >>> calling to get directory entries NFS will always get the labels > > >>> (baring server not supporting it). However this is useless and affects > > >>> performance (ie., this makes servers do extra work and adds to the > > >>> network traffic) when selinux is disabled. It would be useful if NFS > > >>> can check if there is anything that requires those labels, if SElinux > > >>> is enabled or disabled. > > >> > > >> [Adding Chuck Lever to the CC line as I believe he has the most recent > > >> LSM experience from the NFS side - sorry Chuck :)] > > >> > > >> I'll need to ask your patience on this as I am far from a NFS expert. > > >> > > >> Looking through the NFS readdir/getdents code this evening, I was > > >> wondering if the solution in the readdir case is to simply tell the > > >> server you are not interested in the security label by masking out > > >> FATTR4_WORD2_SECURITY_LABEL in the nfs4_readdir_arg->bitmask in > > >> _nfs4_proc_readdir()? Of course this assumes that the security label > > >> genuinely isn't needed in this case (and not requesting it doesn't > > >> bypass access controls or break something on the server side), and we > > >> don't screw up some NFS client side cache by *not* fetching the > > >> security label attribute. > > >> > > >> Is this remotely close to workable, or am I missing something fundamental? > > >> > > > > > > No this is not going to work, as NFS requires labels when labels are > > > indeed needed by the LSM. What I'm looking for is an optimization. > > > What we have is functionality correct but performance might suffer for > > > the standard case of NFSv4.2 seclabel enabled server and clients that > > > don't care about seclabels. > > > > Initial thought: We should ask linux-nfs for help with this. > > I've added them to the Cc: list. > > > > Olga, are you asking if the kernel NFS client module can somehow find > > out whether the rest of the kernel is configured to care about security > > labels before it forms an NFSv4 READDIR or LOOKUP request? > > Yes exactly, but I'm having a hard time trying to figure out how to > use security_ismaclabel() function as has been suggested by Casey. I would suggest either introducing a new hook for your purpose, or altering the existing one to support a form of query that isn't based on a particular xattr name but rather just checking whether the module supports/uses MAC labels at all. Options: 1) NULL argument to the existing hook indicates a general query (could hide a bug in the caller, so not optimal), 2) Add a new bool argument to the existing hook to indicate whether the name should be used, or 3) Add a new hook that doesn't take any arguments. > > > I would certainly like to take the security label query out of every > > LOOKUP operation if that is feasible! > > A LOOKUP doesn't add the seclabel query (by default) like READDIR does > (it's hard-coded in the xdr code). LOOKUP uses server's bitmask and > chooses the version without the seclabel bitmask because no label is > passed into it. It looks like LOOKUP just allocates a label in > nfs_lookup_revalidate_dentry(). So it's not driven by the something > that I see used by the xattr_handle example in the NFS code.
