Re: [PATCH v2 02/23] bpf: initial support for attaching struct ops to cgroups

bot+bpf-ci
2025-10-27T23:48:19Z

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```
commit 31d238f36a0a6a56efa48c847cb776e67ba2f079
Author: Roman Gushchin <roman.gushchin@linux.dev>

bpf: initial support for attaching struct ops to cgroups

When a struct ops is being attached and a bpf link is created, allow to
pass a cgroup fd using bpf attr, so that struct ops can be attached to a
cgroup instead of globally. Attached struct ops doesn't hold a reference
to the cgroup, only preserves cgroup id.

> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index eae907218..7205b813e 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1849,6 +1849,7 @@ struct bpf_struct_ops_link {
> struct bpf_link link;
> struct bpf_map __rcu *map;
> wait_queue_head_t wait_hup;
> + u64 cgroup_id;
> };
>
> struct bpf_link_primer {
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index 45cc5ee19..58664779a 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -13,6 +13,7 @@
> #include <linux/btf_ids.h>
> #include <linux/rcupdate_wait.h>
> #include <linux/poll.h>
> +#include <linux/cgroup.h>
>
> struct bpf_struct_ops_value {
> struct bpf_struct_ops_common_value common;

[ ... ]

> @@ -1359,6 +1360,18 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
> }
> bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_map_lops, NULL,
> attr->link_create.attach_type);
> +#ifdef CONFIG_CGROUPS
> + if (attr->link_create.cgroup.relative_fd) {
> + struct cgroup *cgrp;
> +
> + cgrp = cgroup_get_from_fd(attr->link_create.cgroup.relative_fd);
> + if (IS_ERR(cgrp))
> + return PTR_ERR(cgrp);
^^^^^^^^^^^^^^^^^^^^^^

Can this leak the link and map? In bpf_struct_ops_link_create(), the link
is allocated with kzalloc(GFP_USER) and map is obtained with bpf_map_get()
before this point. If cgroup_get_from_fd() fails, the early return skips
the err_out label which does kfree(link) and bpf_map_put(map).

All other error paths in this function use "err = <error>; goto err_out;"
but this one returns directly.

> +
> + link->cgroup_id = cgroup_id(cgrp);
> + cgroup_put(cgrp);
> + }
> +#endif /* CONFIG_CGROUPS */
> +
> err = bpf_link_prime(&link->link, &link_primer);
> if (err)
> goto err_out;

```

---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
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In-Reply-To-Subject: `bpf: initial support for attaching struct ops to cgroups`
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/18859027430