Re: [PATCH v12 bpf-next 1/9] bpf: Add __bpf_dynptr_data* for in kernel use

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 04/11/2023 00:13, Song Liu wrote:
> Different types of bpf dynptr have different internal data storage.
> Specifically, SKB and XDP type of dynptr may have non-continuous data.
> Therefore, it is not always safe to directly access dynptr->data.
> 
> Add __bpf_dynptr_data and __bpf_dynptr_data_rw to replace direct access to
> dynptr->data.
> 
> Update bpf_verify_pkcs7_signature to use __bpf_dynptr_data instead of
> dynptr->data.
> 
> Signed-off-by: Song Liu <song@kernel.org>
> ---
>   include/linux/bpf.h      |  2 ++
>   kernel/bpf/helpers.c     | 47 ++++++++++++++++++++++++++++++++++++++++
>   kernel/trace/bpf_trace.c | 12 ++++++----
>   3 files changed, 57 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index b4825d3cdb29..eb84caf133df 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1222,6 +1222,8 @@ enum bpf_dynptr_type {
>   
>   int bpf_dynptr_check_size(u32 size);
>   u32 __bpf_dynptr_size(const struct bpf_dynptr_kern *ptr);
> +const void *__bpf_dynptr_data(const struct bpf_dynptr_kern *ptr, u32 len);
> +void *__bpf_dynptr_data_rw(const struct bpf_dynptr_kern *ptr, u32 len);
>   
>   #ifdef CONFIG_BPF_JIT
>   int bpf_trampoline_link_prog(struct bpf_tramp_link *link, struct bpf_trampoline *tr);
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index e46ac288a108..c569c4c43bde 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2611,3 +2611,50 @@ static int __init kfunc_init(void)
>   }
>   
>   late_initcall(kfunc_init);
> +
> +/* Get a pointer to dynptr data up to len bytes for read only access. If
> + * the dynptr doesn't have continuous data up to len bytes, return NULL.
> + */
> +const void *__bpf_dynptr_data(const struct bpf_dynptr_kern *ptr, u32 len)
> +{
> +	enum bpf_dynptr_type type;
> +	int err;
> +
> +	if (!ptr->data)
> +		return NULL;
> +
> +	err = bpf_dynptr_check_off_len(ptr, 0, len);
> +	if (err)
> +		return NULL;
> +	type = bpf_dynptr_get_type(ptr);
> +
> +	switch (type) {
> +	case BPF_DYNPTR_TYPE_LOCAL:
> +	case BPF_DYNPTR_TYPE_RINGBUF:
> +		return ptr->data + ptr->offset;
> +	case BPF_DYNPTR_TYPE_SKB:
> +		return skb_pointer_if_linear(ptr->data, ptr->offset, len);
> +	case BPF_DYNPTR_TYPE_XDP:
> +	{
> +		void *xdp_ptr = bpf_xdp_pointer(ptr->data, ptr->offset, len);
> +
> +		if (IS_ERR_OR_NULL(xdp_ptr))
> +			return NULL;
> +		return xdp_ptr;
> +	}
> +	default:
> +		WARN_ONCE(true, "unknown dynptr type %d\n", type);
> +		return NULL;
> +	}
> +}
> +
> +/* Get a pointer to dynptr data up to len bytes for read write access. If
> + * the dynptr doesn't have continuous data up to len bytes, or the dynptr
> + * is read only, return NULL.
> + */
> +void *__bpf_dynptr_data_rw(const struct bpf_dynptr_kern *ptr, u32 len)
> +{
> +	if (__bpf_dynptr_is_rdonly(ptr))
> +		return NULL;
> +	return (void *)__bpf_dynptr_data(ptr, len);
> +}
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index df697c74d519..d525a22b8d56 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1378,6 +1378,8 @@ __bpf_kfunc int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
>   			       struct bpf_dynptr_kern *sig_ptr,
>   			       struct bpf_key *trusted_keyring)
>   {
> +	const void *data, *sig;
> +	u32 data_len, sig_len;
>   	int ret;
>   
>   	if (trusted_keyring->has_ref) {
> @@ -1394,10 +1396,12 @@ __bpf_kfunc int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
>   			return ret;
>   	}
>   
> -	return verify_pkcs7_signature(data_ptr->data,
> -				      __bpf_dynptr_size(data_ptr),
> -				      sig_ptr->data,
> -				      __bpf_dynptr_size(sig_ptr),
> +	data_len = __bpf_dynptr_size(data_ptr);
> +	data = __bpf_dynptr_data(data_ptr, data_len);
> +	sig_len = __bpf_dynptr_size(sig_ptr);
> +	sig = __bpf_dynptr_data(sig_ptr, sig_len);
> +
> +	return verify_pkcs7_signature(data, data_len, sig, sig_len,
>   				      trusted_keyring->key,
>   				      VERIFYING_UNSPECIFIED_SIGNATURE, NULL,
>   				      NULL);

Acked-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>