On Thu, Nov 12, 2020 at 4:13 PM Paul Moore wrote: > > On Tue, Nov 10, 2020 at 10:30 PM Lokesh Gidra wrote: > > On Tue, Nov 10, 2020 at 6:13 PM Paul Moore wrote: > > > On Tue, Nov 10, 2020 at 1:24 PM Lokesh Gidra wrote: > > > > On Mon, Nov 9, 2020 at 7:12 PM Paul Moore wrote: > > > > > On Fri, Nov 6, 2020 at 10:56 AM Lokesh Gidra wrote: > > > > > > > > > > > > From: Daniel Colascione > > > > > > > > > > > > This change uses the anon_inodes and LSM infrastructure introduced in > > > > > > the previous patches to give SELinux the ability to control > > > > > > anonymous-inode files that are created using the new > > > > > > anon_inode_getfd_secure() function. > > > > > > > > > > > > A SELinux policy author detects and controls these anonymous inodes by > > > > > > adding a name-based type_transition rule that assigns a new security > > > > > > type to anonymous-inode files created in some domain. The name used > > > > > > for the name-based transition is the name associated with the > > > > > > anonymous inode for file listings --- e.g., "[userfaultfd]" or > > > > > > "[perf_event]". > > > > > > > > > > > > Example: > > > > > > > > > > > > type uffd_t; > > > > > > type_transition sysadm_t sysadm_t : anon_inode uffd_t "[userfaultfd]"; > > > > > > allow sysadm_t uffd_t:anon_inode { create }; > > > > > > > > > > > > (The next patch in this series is necessary for making userfaultfd > > > > > > support this new interface. The example above is just > > > > > > for exposition.) > > > > > > > > > > > > Signed-off-by: Daniel Colascione > > > > > > Signed-off-by: Lokesh Gidra > > > > > > --- > > > > > > security/selinux/hooks.c | 53 +++++++++++++++++++++++++++++ > > > > > > security/selinux/include/classmap.h | 2 ++ > > > > > > 2 files changed, 55 insertions(+) > > > > > > > > > > > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > > > > > > index 6b1826fc3658..1c0adcdce7a8 100644 > > > > > > --- a/security/selinux/hooks.c > > > > > > +++ b/security/selinux/hooks.c > > > > > > @@ -2927,6 +2927,58 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir, > > > > > > return 0; > > > > > > } > > > > > > > > > > > > +static int selinux_inode_init_security_anon(struct inode *inode, > > > > > > + const struct qstr *name, > > > > > > + const struct inode *context_inode) > > > > > > +{ > > > > > > + const struct task_security_struct *tsec = selinux_cred(current_cred()); > > > > > > + struct common_audit_data ad; > > > > > > + struct inode_security_struct *isec; > > > > > > + int rc; > > > > > > + > > > > > > + if (unlikely(!selinux_initialized(&selinux_state))) > > > > > > + return 0; > > > > > > + > > > > > > + isec = selinux_inode(inode); > > > > > > + > > > > > > + /* > > > > > > + * We only get here once per ephemeral inode. The inode has > > > > > > + * been initialized via inode_alloc_security but is otherwise > > > > > > + * untouched. > > > > > > + */ > > > > > > + > > > > > > + if (context_inode) { > > > > > > + struct inode_security_struct *context_isec = > > > > > > + selinux_inode(context_inode); > > > > > > + isec->sclass = context_isec->sclass; > > > > > > + isec->sid = context_isec->sid; > > > > > > > > > > I suppose this isn't a major concern given the limited usage at the > > > > > moment, but I wonder if it would be a good idea to make sure the > > > > > context_inode's SELinux label is valid before we assign it to the > > > > > anonymous inode? If it is invalid, what should we do? Do we attempt > > > > > to (re)validate it? Do we simply fallback to the transition approach? > > > > > > > > Frankly, I'm not too familiar with SELinux. Originally this patch > > > > series was developed by Daniel, in consultation with Stephen Smalley. > > > > In my (probably naive) opinion we should fallback to transition > > > > approach. But I'd request you to tell me if this needs to be addressed > > > > now, and if so then what's the right approach. > > > > > > > > If the decision is to address this now, then what's the best way to > > > > check the SELinux label validity? > > > > > > You can check to see if an inode's label is valid by looking at the > > > isec->initialized field; if it is LABEL_INITIALIZED then it is all > > > set, if it is any other value then the label isn't entirely correct. > > > It may have not have ever been fully initialized (and has a default > > > value) or it may have live on a remote filesystem where the host has > > > signaled that the label has changed (and the label is now outdated). > > > > > > This patchset includes support for userfaultfd, which means we don't > > > really have to worry about the remote fs problem, but the > > > never-fully-initialized problem could be real in this case. Normally > > > we would revalidate an inode in SELinux by calling > > > __inode_security_revalidate() which requires either a valid dentry or > > > one that can be found via the inode; does d_find_alias() work on > > > userfaultfd inodes? > > > > > > If all else fails, it seems like the safest approach would be to > > > simply fail the selinux_inode_init_security_anon() call if a > > > context_inode was supplied and the label wasn't valid. If we later > > > decide to change it to falling back to the transition approach we can > > > do that, we can't go the other way (from transition to error). > > > > I'm not sure about d_find_alias() on userfaultfd inodes. But it seems > > ok to fail selinux_inode_init_security_anon() to begin with. > > I'm okay with simply failing here, but I'm growing a bit concerned > that this patchset hasn't been well tested. That is a problem. > > > > > > This brings up another question, and requirement - what testing are > > > > > you doing for this patchset? We require that new SELinux kernel > > > > > functionality includes additions to the SELinux test suite to help > > > > > verify the functionality. I'm also *strongly* encouraging that new > > > > > contributions come with updates to The SELinux Notebook. If you are > > > > > unsure about what to do for either, let us know and we can help get > > > > > you started. > > > > > > > > > > * https://github.com/SELinuxProject/selinux-testsuite > > > > > * https://github.com/SELinuxProject/selinux-notebook > > > > > > > > > I'd definitely need help with both of these. Kindly guide how to proceed. > > > > > > Well, perhaps the best way to start is to explain how you have been > > > testing this so far and then using that information to draft a test > > > for the testsuite. > > > > As I said in my previous reply, Daniel worked on this patch along with > > Stephan Smalley. Here's the conversation regarding testing from back > > then: > > https://lore.kernel.org/lkml/CAEjxPJ4iquFSBfEj+UEFLUFHPsezuQ-Bzv09n+WgOWk38Nyw3w@mail.gmail.com/ > > > > There have been only minor changes (fixing comments/coding-style), > > except for addressing a double free issue with userfaultfd_ctx since > > last time it was tested as per the link above. > > I should probably be more clear. I honestly don't care who originally > wrote the patch, the simple fact is that you are the one who is > posting it *now* for inclusion in the kernel; at the very least I > expect you to be able to demonstrate that you are able to reliably > test this functionality and prove it is working. While being able to > test this submission initially is important, it is far more important > to have the tests and docs necessary to maintain this functionality > long term. Perhaps you and/or Google will continue to contribute and > support this functionality long term, but it would be irresponsible of > me to assume that to be true; both people and companies come and go > but code has a tendency to live forever. > > Let's start again; how have you been testing this code? > I have created a cuttlefish build and have tested with the attached userfaultfd program: 1) Without these kernel patches the program executes without any restrictions vsoc_x86_64:/ $ ./system/bin/userfaultfdSimple api: 170 features: 511 ioctls: 9223372036854775811 read: Try again 2) With these patches applied but without any policy the 'permission denied' is thrown vsoc_x86_64:/ $ ./system/bin/userfaultfdSimple syscall(userfaultfd): Permission denied with the following logcat message: 11-18 14:21:44.041 3130 3130 W userfaultfdSimp: type=1400 audit(0.0:107): avc: denied { create } for dev="anon_inodefs" ino=45031 scontext=u:r:shell:s0 tcontext=u:object_r:shell:s0 tclass=anon_inode permissive=0 3) With the attached .te policy file in place the following output is observed, confirming that the patch is working as intended. vsoc_x86_64:/ $ ./vendor/bin/userfaultfdSimple UFFDIO_API: Permission denied with the following logcat message: 11-18 14:33:29.142 2028 2028 W userfaultfdSimp: type=1400 audit(0.0:104): avc: denied { ioctl } for path="anon_inode:[userfaultfd]" dev="anon_inodefs" ino=41169 ioctlcmd=0xaa3f scontext=u:r:userfaultfdSimple:s0 tcontext=u:object_r:uffd_t:s0 tclass=anon_inode permissive=0 > -- > paul moore > www.paul-moore.com