On Thu, Feb 20, 2020 at 10:50 AM Daniel Colascione <dancol@xxxxxxxxxx> wrote: > > On Thu, Feb 20, 2020 at 10:11 AM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: > > > > On 2/17/2020 4:14 PM, Paul Moore wrote: > > > On Thu, Feb 13, 2020 at 2:41 PM Stephen Smalley <sds@xxxxxxxxxxxxx> wrote: > > >> Add support for labeling and controlling access to files attached to anon > > >> inodes. Introduce extended interfaces for creating such files to permit > > >> passing a related file as an input to decide how to label the anon > > >> inode. Define a security hook for initializing the anon inode security > > >> attributes. Security attributes are either inherited from a related file > > >> or determined based on some combination of the creating task and policy > > >> (in the case of SELinux, using type_transition rules). As an > > >> example user of the inheritance support, convert kvm to use the new > > >> interface for passing the related file so that the anon inode can inherit > > >> the security attributes of /dev/kvm and provide consistent access control > > >> for subsequent ioctl operations. Other users of anon inodes, including > > >> userfaultfd, will default to the transition-based mechanism instead. > > >> > > >> Compared to the series in > > >> https://lore.kernel.org/selinux/20200211225547.235083-1-dancol@xxxxxxxxxx/, > > >> this approach differs in that it does not require creation of a separate > > >> anonymous inode for each file (instead storing the per-instance security > > >> information in the file security blob), it applies labeling and control > > >> to all users of anonymous inodes rather than requiring opt-in via a new > > >> flag, it supports labeling based on a related inode if provided, > > >> it relies on type transitions to compute the label of the anon inode > > >> when there is no related inode, and it does not require introducing a new > > >> security class for each user of anonymous inodes. > > >> > > >> On the other hand, the approach in this patch does expose the name passed > > >> by the creator of the anon inode to the policy (an indirect mapping could > > >> be provided within SELinux if these names aren't considered to be stable), > > >> requires the definition of type_transition rules to distinguish userfaultfd > > >> inodes from proc inodes based on type since they share the same class, > > >> doesn't support denying the creation of anonymous inodes (making the hook > > >> added by this patch return something other than void is problematic due to > > >> it being called after the file is already allocated and error handling in > > >> the callers can't presently account for this scenario and end up calling > > >> release methods multiple times), and may be more expensive > > >> (security_transition_sid overhead on each anon inode allocation). > > >> > > >> We are primarily posting this RFC patch now so that the two different > > >> approaches can be concretely compared. We anticipate a hybrid of the > > >> two approaches being the likely outcome in the end. In particular > > >> if support for allocating a separate inode for each of these files > > >> is acceptable, then we would favor storing the security information > > >> in the inode security blob and using it instead of the file security > > >> blob. > > > Bringing this back up in hopes of attracting some attention from the > > > fs-devel crowd and Al. As Stephen already mentioned, from a SELinux > > > perspective we would prefer to attach the security blob to the inode > > > as opposed to the file struct; does anyone have any objections to > > > that? > > > > Sorry for the delay - been sick the past few days. > > > > I agree that the inode is a better place than the file for information > > about the inode. This is especially true for Smack, which uses > > multiple extended attributes in some cases. I don't believe that any > > except the access label will be relevant to anonymous inodes, but > > I can imagine security modules with policies that would. > > > > I am always an advocate of full xattr support. It goes a long > > way in reducing the number and complexity of special case interfaces. > > It sounds like we have broad consensus on using the inode to hold > security information, implying that anon_inodes should create new > inodes. Do any of the VFS people want to object? Ping?
