On Wed, Jan 6, 2021 at 10:55 PM Lokesh Gidra <lokeshgi...@google.com> wrote: > On Wed, Jan 6, 2021 at 7:03 PM Paul Moore <p...@paul-moore.com> wrote: > > On Wed, Nov 11, 2020 at 8:54 PM Lokesh Gidra <lokeshgi...@google.com> wrote: > > > From: Daniel Colascione <dan...@google.com> > > > > > > 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 <dan...@google.com> > > > Signed-off-by: Lokesh Gidra <lokeshgi...@google.com> > > > --- > > > security/selinux/hooks.c | 56 +++++++++++++++++++++++++++++ > > > security/selinux/include/classmap.h | 2 ++ > > > 2 files changed, 58 insertions(+) > > > > > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > > > index 6b1826fc3658..d092aa512868 100644 > > > --- a/security/selinux/hooks.c > > > +++ b/security/selinux/hooks.c > > > @@ -2927,6 +2927,61 @@ 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); > > > + if (context_isec->initialized != LABEL_INITIALIZED) > > > + return -EACCES; > > > + > > > + isec->sclass = context_isec->sclass; > > > > Taking the object class directly from the context_inode is > > interesting, and I suspect problematic. In the case below where no > > context_inode is supplied the object class is set to > > SECCLASS_ANON_INODE, which is correct, but when a context_inode is > > supplied there is no guarantee that the object class will be set to > > SECCLASS_ANON_INODE. This could both pose a problem for policy > > writers (how do you distinguish the anon inode from other normal file > > inodes in this case?) as well as an outright fault later in this > > function when we try to check the ANON_INODE__CREATE on an object > > other than a SECCLASS_ANON_INODE object. > > > Thanks for catching this. I'll initialize 'sclass' unconditionally to > SECCLASS_ANON_INODE in the next version. Also, do you think I should > add a check that context_inode's sclass must be SECCLASS_ANON_INODE to > confirm that we never receive a regular inode as context_inode?
This is one of the reasons why I was asking if you ever saw the need to use a regular inode here. It seems much safer to me to add a check to ensure that context_inode is SECCLASS_ANON_INODE and return an error otherwise; I would also suggest emitting an error using pr_err() with something along the lines of "SELinux: initializing anonymous inode with inappropriate inode" (or something similar). If something changes in the future we can always reconsider this restriction. > > It works in the userfaultfd case because the context_inode is > > originally created with this function so the object class is correctly > > set to SECCLASS_ANON_INODE, but can we always guarantee that to be the > > case? Do we ever need or want to support using a context_inode that > > is not SECCLASS_ANON_INODE? > > I don't think there is any requirement of supporting context_inode > which isn't anon-inode. And even if there is, as you described > earlier, for ANON_INODE__CREATE to work the sclass has to be > SECCLASS_ANON_INODE. I'll appreciate comments on this from others, > particularly Daniel and Stephen who originally discussed and > implemented this patch. I would encourage you not to wait too long for additional feedback before sending the next revision. -- paul moore www.paul-moore.com