From: Jakub Sitnicki <jakub@cloudflare.com>
Date: Sun, 31 May 2020 10:28:39 +0200
Subject: bpf, cgroup: Return ENOLINK for auto-detached links on update
Patch-mainline: v5.8-rc1
Git-commit: 0c047ecbb7bab4c1d2136f5f04bb47a66a9a12b8
References: bsc#1177028

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: 0c991ebc8c69 ("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
Acked-by: Gary Lin <glin@suse.com>
---
 kernel/bpf/cgroup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -595,7 +595,7 @@ static int cgroup_bpf_replace(struct bpf
 	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) {