On Wed, Oct 26, 2016 at 08:56:39AM +0200, Mickaël Salaün wrote: > This new arraymap looks like a set and brings new properties: > * strong typing of entries: the eBPF functions get the array type of > elements instead of CONST_PTR_TO_MAP (e.g. > CONST_PTR_TO_LANDLOCK_HANDLE_FS); > * force sequential filling (i.e. replace or append-only update), which > allow quick browsing of all entries. > > This strong typing is useful to statically check if the content of a map > can be passed to an eBPF function. For example, Landlock use it to store > and manage kernel objects (e.g. struct file) instead of dealing with > userland raw data. This improve efficiency and ensure that an eBPF > program can only call functions with the right high-level arguments. > > The enum bpf_map_handle_type list low-level types (e.g. > BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) which are identified when > updating a map entry (handle). This handle types are used to infer a > high-level arraymap type which are listed in enum bpf_map_array_type > (e.g. BPF_MAP_ARRAY_TYPE_LANDLOCK_FS). > > For now, this new arraymap is only used by Landlock LSM (cf. next > commits) but it could be useful for other needs. > > Changes since v3: > * make handle arraymap safe (RCU) and remove buggy synchronize_rcu() > * factor out the arraymay walk > > Changes since v2: > * add a RLIMIT_NOFILE-based limit to the maximum number of arraymap > handle entries (suggested by Andy Lutomirski) > * remove useless checks > > Changes since v1: > * arraymap of handles replace custom checker groups > * simpler userland API [...] > + case BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD: > + handle_file = fget(handle->fd); > + if (IS_ERR(handle_file)) > + return ERR_CAST(handle_file); > + /* check if the FD is tied to a user mount point */ > + if (unlikely(handle_file->f_path.mnt->mnt_flags & MNT_INTERNAL)) { > + fput(handle_file); > + return ERR_PTR(-EINVAL); > + } > + path_get(&handle_file->f_path); > + ret = kmalloc(sizeof(*ret), GFP_KERNEL); > + ret->path = handle_file->f_path; > + fput(handle_file); You can use fdget() and fdput() here because the reference to handle_file is dropped before the end of the syscall. > + break; > + case BPF_MAP_HANDLE_TYPE_UNSPEC: > + default: > + return ERR_PTR(-EINVAL); > + } > + ret->type = handle_type; > + return ret; > +} > + > +static void *nop_map_lookup_elem(struct bpf_map *map, void *key) > +{ > + return ERR_PTR(-EINVAL); > +} > + > +/* called from syscall or from eBPF program */ > +static int landlock_array_map_update_elem(struct bpf_map *map, void *key, > + void *value, u64 map_flags) > +{ This being callable from eBPF context is IMO pretty surprising and should at least be well-documented. Also: What is the usecase here?
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