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SubjectRe: [PATCH bpf-next v3 1/7] bpf: Refactor trampoline update code
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On 3/4/20 4:47 PM, KP Singh wrote:
> From: KP Singh <kpsingh@google.com>
>
> As we need to introduce a third type of attachment for trampolines, the
> flattened signature of arch_prepare_bpf_trampoline gets even more
> complicated.
>
> Refactor the prog and count argument to arch_prepare_bpf_trampoline to
> use bpf_tramp_progs to simplify the addition and accounting for new
> attachment types.
>
> Signed-off-by: KP Singh <kpsingh@google.com>
> Acked-by: Andrii Nakryiko <andriin@fb.com>

[...]
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index c498f0fffb40..9f7e0328a644 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -320,6 +320,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
> struct bpf_struct_ops_value *uvalue, *kvalue;
> const struct btf_member *member;
> const struct btf_type *t = st_ops->type;
> + struct bpf_tramp_progs *tprogs = NULL;
> void *udata, *kdata;
> int prog_fd, err = 0;
> void *image;
> @@ -425,10 +426,18 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
> goto reset_unlock;
> }
>
> + tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
> + if (!tprogs) {
> + err = -ENOMEM;
> + goto reset_unlock;
> + }
> +

Looking over the code again, I'm quite certain that here's a memleak
since the kcalloc() is done in the for_each_member() loop in the ops
update but then going out of scope and in the exit path we only kfree
the last tprogs.

> + tprogs[BPF_TRAMP_FENTRY].progs[0] = prog;
> + tprogs[BPF_TRAMP_FENTRY].nr_progs = 1;
> err = arch_prepare_bpf_trampoline(image,
> st_map->image + PAGE_SIZE,
> &st_ops->func_models[i], 0,
> - &prog, 1, NULL, 0, NULL);
> + tprogs, NULL);
> if (err < 0)
> goto reset_unlock;
>
> @@ -469,6 +478,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
> memset(uvalue, 0, map->value_size);
> memset(kvalue, 0, map->value_size);
> unlock:
> + kfree(tprogs);
> mutex_unlock(&st_map->lock);
> return err;
> }

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