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authorAndrii Nakryiko <andriin@fb.com>2020-03-29 19:59:59 -0700
committerAlexei Starovoitov <ast@kernel.org>2020-03-30 17:36:33 -0700
commit0c991ebc8c69d29b7fc44db17075c5aa5253e2ab (patch)
treee61172384e68887343d57f1e40d47c2e5ecc98cc /kernel/bpf/cgroup.c
parentaf6eea57437a830293eab56246b6025cc7d46ee7 (diff)
bpf: Implement bpf_prog replacement for an active bpf_cgroup_link
Add new operation (LINK_UPDATE), which allows to replace active bpf_prog from under given bpf_link. Currently this is only supported for bpf_cgroup_link, but will be extended to other kinds of bpf_links in follow-up patches. For bpf_cgroup_link, implemented functionality matches existing semantics for direct bpf_prog attachment (including BPF_F_REPLACE flag). User can either unconditionally set new bpf_prog regardless of which bpf_prog is currently active under given bpf_link, or, optionally, can specify expected active bpf_prog. If active bpf_prog doesn't match expected one, no changes are performed, old bpf_link stays intact and attached, operation returns a failure. cgroup_bpf_replace() operation is resolving race between auto-detachment and bpf_prog update in the same fashion as it's done for bpf_link detachment, except in this case update has no way of succeeding because of target cgroup marked as dying. So in this case error is returned. Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200330030001.2312810-3-andriin@fb.com
Diffstat (limited to 'kernel/bpf/cgroup.c')
-rw-r--r--kernel/bpf/cgroup.c80
1 files changed, 80 insertions, 0 deletions
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index c24029937431..80676fc00d81 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -500,6 +500,86 @@ cleanup:
return err;
}
+/* Swap updated BPF program for given link in effective program arrays across
+ * all descendant cgroups. This function is guaranteed to succeed.
+ */
+static void replace_effective_prog(struct cgroup *cgrp,
+ enum bpf_attach_type type,
+ struct bpf_cgroup_link *link)
+{
+ struct bpf_prog_array_item *item;
+ struct cgroup_subsys_state *css;
+ struct bpf_prog_array *progs;
+ struct bpf_prog_list *pl;
+ struct list_head *head;
+ struct cgroup *cg;
+ int pos;
+
+ css_for_each_descendant_pre(css, &cgrp->self) {
+ struct cgroup *desc = container_of(css, struct cgroup, self);
+
+ if (percpu_ref_is_zero(&desc->bpf.refcnt))
+ continue;
+
+ /* find position of link in effective progs array */
+ for (pos = 0, cg = desc; cg; cg = cgroup_parent(cg)) {
+ if (pos && !(cg->bpf.flags[type] & BPF_F_ALLOW_MULTI))
+ continue;
+
+ head = &cg->bpf.progs[type];
+ list_for_each_entry(pl, head, node) {
+ if (!prog_list_prog(pl))
+ continue;
+ if (pl->link == link)
+ goto found;
+ pos++;
+ }
+ }
+found:
+ BUG_ON(!cg);
+ progs = rcu_dereference_protected(
+ desc->bpf.effective[type],
+ lockdep_is_held(&cgroup_mutex));
+ item = &progs->items[pos];
+ WRITE_ONCE(item->prog, link->link.prog);
+ }
+}
+
+/**
+ * __cgroup_bpf_replace() - Replace link's program and propagate the change
+ * to descendants
+ * @cgrp: The cgroup which descendants to traverse
+ * @link: A link for which to replace BPF program
+ * @type: Type of attach operation
+ *
+ * Must be called with cgroup_mutex held.
+ */
+int __cgroup_bpf_replace(struct cgroup *cgrp, struct bpf_cgroup_link *link,
+ struct bpf_prog *new_prog)
+{
+ struct list_head *progs = &cgrp->bpf.progs[link->type];
+ struct bpf_prog *old_prog;
+ struct bpf_prog_list *pl;
+ bool found = false;
+
+ if (link->link.prog->type != new_prog->type)
+ return -EINVAL;
+
+ list_for_each_entry(pl, progs, node) {
+ if (pl->link == link) {
+ found = true;
+ break;
+ }
+ }
+ if (!found)
+ return -ENOENT;
+
+ old_prog = xchg(&link->link.prog, new_prog);
+ replace_effective_prog(cgrp, link->type, link);
+ bpf_prog_put(old_prog);
+ return 0;
+}
+
static struct bpf_prog_list *find_detach_entry(struct list_head *progs,
struct bpf_prog *prog,
struct bpf_cgroup_link *link,