linux-kernel - Re: [PATCH bpf] bpf: btf: fix truncated last_member_type_id in btf_struct

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Date:   Fri, 9 Sep 2022 11:17:52 -0700
From:   Martin KaFai Lau <martin.lau@...ux.dev>
To:     Lorenz Bauer <oss@....io>
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH bpf] bpf: btf: fix truncated last_member_type_id in
 btf_struct_resolve

On 9/9/22 2:21 AM, Lorenz Bauer wrote:
> When trying to finish resolving a struct member, btf_struct_resolve
> saves the member type id in a u16 temporary variable. This truncates
> the 32 bit type id value if it exceeds UINT16_MAX.
> 
> As a result, structs that have members with type ids > UINT16_MAX and
> which need resolution will fail with a message like this:
> 
>      [67414] STRUCT ff_device size=120 vlen=12
>          effect_owners type_id=67434 bits_offset=960 Member exceeds struct_size
> 
> Fix this by changing the type of last_member_type_id to u32.
> 
> Fixes: eb3f595dab40 ("bpf: btf: Validate type reference")

The fix tag should be

Fixes: a0791f0df7d2 ("bpf: fix BTF limits")

> Signed-off-by: Lorenz Bauer <oss@....io>
> ---
>   kernel/bpf/btf.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 7e64447659f3..36fd4b509294 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -3128,7 +3128,7 @@ static int btf_struct_resolve(struct btf_verifier_env *env,
>   	if (v->next_member) {
>   		const struct btf_type *last_member_type;
>   		const struct btf_member *last_member;
> -		u16 last_member_type_id;
> +		u32 last_member_type_id;

The change makes sense.

The kernel's vmlinux and module btf parsing doesn't go through this 
resolve check though.  Are you trying to __sys_bpf(BPF_BTF_LOAD) the btf 
from the vmlinux file into the kernel ?