diff options
authorLorenz Bauer <>2020-06-08 17:22:01 +0100
committerAlexei Starovoitov <>2020-06-09 11:21:43 -0700
commit248e00ac47d64e153b9c50f45aad73cd61894a73 (patch)
parent26afa0a4eb3fd87757f9de56ec5db5a03b14e120 (diff)
bpf: cgroup: Allow multi-attach program to replace itself
When using BPF_PROG_ATTACH to attach a program to a cgroup in BPF_F_ALLOW_MULTI mode, it is not possible to replace a program with itself. This is because the check for duplicate programs doesn't take the replacement program into account. Replacing a program with itself might seem weird, but it has some uses: first, it allows resetting the associated cgroup storage. Second, it makes the API consistent with the non-ALLOW_MULTI usage, where it is possible to replace a program with itself. Third, it aligns BPF_PROG_ATTACH with bpf_link, where replacing itself is also supported. Sice this code has been refactored a few times this change will only apply to v5.7 and later. Adjustments could be made to commit 1020c1f24a94 ("bpf: Simplify __cgroup_bpf_attach") and commit d7bf2c10af05 ("bpf: allocate cgroup storage entries on attaching bpf programs") as well as commit 324bda9e6c5a ("bpf: multi program support for cgroup+bpf") Fixes: af6eea57437a ("bpf: Implement bpf_link-based cgroup BPF program attachment") Signed-off-by: Lorenz Bauer <> Signed-off-by: Alexei Starovoitov <> Link:
2 files changed, 8 insertions, 1 deletions
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index fdf7836..4d76f16 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -378,7 +378,7 @@ static struct bpf_prog_list *find_attach_entry(struct list_head *progs,
list_for_each_entry(pl, progs, node) {
- if (prog && pl->prog == prog)
+ if (prog && pl->prog == prog && prog != replace_prog)
/* disallow attaching the same prog twice */
return ERR_PTR(-EINVAL);
if (link && pl->link == link)
diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c b/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c
index 139f8e8..b549fcf 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_attach_multi.c
@@ -230,6 +230,13 @@ void test_cgroup_attach_multi(void)
"prog_replace", "errno=%d\n", errno))
goto err;
+ /* replace program with itself */
+ attach_opts.replace_prog_fd = allow_prog[6];
+ if (CHECK(bpf_prog_attach_xattr(allow_prog[6], cg1,
+ BPF_CGROUP_INET_EGRESS, &attach_opts),
+ "prog_replace", "errno=%d\n", errno))
+ goto err;
value = 0;
CHECK_FAIL(bpf_map_update_elem(map_fd, &key, &value, 0));