bpf, cgroup: Return ENOLINK for auto-detached links on update

Failure to update a bpf_link because it has been auto-detached by a dying
cgroup currently results in EINVAL error, even though the arguments passed
to bpf() syscall are not wrong.

bpf_links attaching to netns in this case will return ENOLINK, which
carries the message that the link is no longer attached to anything.

Change cgroup bpf_links to do the same to keep the uAPI errors consistent.

Fixes: e7b78a6a310b ("bpf: Implement bpf_prog replacement for an active bpf_cgroup_link")
Suggested-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200531082846.2117903-6-jakub@cloudflare.com

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 5c0e964105ac9070d284d160da7b43305ec8afda..fdf7836750a3352caaf34dd13085c9fcac4c1c3a 100644 (file)
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -595,7 +595,7 @@ static int cgroup_bpf_replace(struct bpf_link *link, struct bpf_prog *new_prog,
        mutex_lock(&cgroup_mutex);
        /* link might have been auto-released by dying cgroup, so fail */
        if (!cg_link->cgroup) {
-               ret = -EINVAL;
+               ret = -ENOLINK;
                goto out_unlock;
        }
        if (old_prog && link->prog != old_prog) {