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SubjectRe: [PATCH v3 bpf-next 04/14] bpf: allocate cgroup storage entries on attaching bpf programs
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On 07/20/2018 07:45 PM, Roman Gushchin wrote:
> If a bpf program is using cgroup local storage, allocate
> a bpf_cgroup_storage structure automatically on attaching the program
> to a cgroup and save the pointer into the corresponding bpf_prog_list
> entry.
> Analogically, release the cgroup local storage on detaching
> of the bpf program.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Acked-by: Martin KaFai Lau <kafai@fb.com>
> ---
> include/linux/bpf-cgroup.h | 1 +
> kernel/bpf/cgroup.c | 28 ++++++++++++++++++++++++++--
> 2 files changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
> index 1b1b4e94d77d..f37347331fdb 100644
> --- a/include/linux/bpf-cgroup.h
> +++ b/include/linux/bpf-cgroup.h
> @@ -42,6 +42,7 @@ struct bpf_cgroup_storage {
> struct bpf_prog_list {
> struct list_head node;
> struct bpf_prog *prog;
> + struct bpf_cgroup_storage *storage;
> };
>
> struct bpf_prog_array;
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index badabb0b435c..986ff18ef92e 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -34,6 +34,8 @@ void cgroup_bpf_put(struct cgroup *cgrp)
> list_for_each_entry_safe(pl, tmp, progs, node) {
> list_del(&pl->node);
> bpf_prog_put(pl->prog);
> + bpf_cgroup_storage_unlink(pl->storage);
> + bpf_cgroup_storage_free(pl->storage);
> kfree(pl);
> static_branch_dec(&cgroup_bpf_enabled_key);
> }
> @@ -188,6 +190,7 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
> {
> struct list_head *progs = &cgrp->bpf.progs[type];
> struct bpf_prog *old_prog = NULL;
> + struct bpf_cgroup_storage *storage, *old_storage = NULL;
> struct cgroup_subsys_state *css;
> struct bpf_prog_list *pl;
> bool pl_was_allocated;
> @@ -210,6 +213,10 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
> if (prog_list_length(progs) >= BPF_CGROUP_MAX_PROGS)
> return -E2BIG;
>
> + storage = bpf_cgroup_storage_alloc(prog);
> + if (IS_ERR(storage))
> + return -ENOMEM;
> +
> if (flags & BPF_F_ALLOW_MULTI) {
> list_for_each_entry(pl, progs, node)
> if (pl->prog == prog)
> @@ -217,24 +224,33 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
> return -EINVAL;
>
> pl = kmalloc(sizeof(*pl), GFP_KERNEL);
> - if (!pl)
> + if (!pl) {
> + bpf_cgroup_storage_free(storage);
> return -ENOMEM;
> + }

Above code is:

storage = bpf_cgroup_storage_alloc(prog);
if (IS_ERR(storage))
return -ENOMEM;

if (flags & BPF_F_ALLOW_MULTI) {
list_for_each_entry(pl, progs, node)
if (pl->prog == prog)
/* disallow attaching the same prog twice */
return -EINVAL;

pl = kmalloc(sizeof(*pl), GFP_KERNEL);
if (!pl) {
bpf_cgroup_storage_free(storage);
return -ENOMEM;
}

Given bpf_cgroup_storage_alloc() only changes the mem and prepares (kmallocs)
the local storage buffer, we would leak it above where we attach the same
prog twice, no?

> +
> pl_was_allocated = true;
> pl->prog = prog;
> + pl->storage = storage;
> list_add_tail(&pl->node, progs);
> } else {
> if (list_empty(progs)) {
> pl = kmalloc(sizeof(*pl), GFP_KERNEL);
> - if (!pl)
> + if (!pl) {
> + bpf_cgroup_storage_free(storage);
> return -ENOMEM;
> + }
> pl_was_allocated = true;
> list_add_tail(&pl->node, progs);
> } else {
> pl = list_first_entry(progs, typeof(*pl), node);
> old_prog = pl->prog;
> + old_storage = pl->storage;
> + bpf_cgroup_storage_unlink(old_storage);
> pl_was_allocated = false;
> }
> pl->prog = prog;
> + pl->storage = storage;
> }
>
> cgrp->bpf.flags[type] = flags;
> @@ -257,10 +273,13 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
> }
>
> static_branch_inc(&cgroup_bpf_enabled_key);
> + if (old_storage)
> + bpf_cgroup_storage_free(old_storage);
> if (old_prog) {
> bpf_prog_put(old_prog);
> static_branch_dec(&cgroup_bpf_enabled_key);
> }
> + bpf_cgroup_storage_link(storage, cgrp, type);
> return 0;
>
> cleanup:
> @@ -276,6 +295,9 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
>
> /* and cleanup the prog list */
> pl->prog = old_prog;
> + bpf_cgroup_storage_free(pl->storage);
> + pl->storage = old_storage;
> + bpf_cgroup_storage_link(old_storage, cgrp, type);
> if (pl_was_allocated) {
> list_del(&pl->node);
> kfree(pl);
> @@ -356,6 +378,8 @@ int __cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
>
> /* now can actually delete it from this cgroup list */
> list_del(&pl->node);
> + bpf_cgroup_storage_unlink(pl->storage);
> + bpf_cgroup_storage_free(pl->storage);
> kfree(pl);
> if (list_empty(progs))
> /* last program was detached, reset flags to zero */
>

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