[v10,bpf-next,1/9] bpf: Add __bpf_dynptr_data* for in kernel use

Commit Message

Song Liu Nov. 3, 2023, 9:45 p.m. UTC

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 <[e-mail]>
---
 include/linux/bpf.h      |  2 ++
 kernel/bpf/helpers.c     | 47 ++++++++++++++++++++++++++++++++++++++++
 kernel/trace/bpf_trace.c | 10 +++++----
 3 files changed, 55 insertions(+), 4 deletions(-)

Comments

Andrii Nakryiko Nov. 3, 2023, 10:02 p.m. UTC | #1

On Fri, Nov 3, 2023 at 2:46 PM Song Liu <[e-mail]> 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 <[e-mail]>
> ---
>  include/linux/bpf.h      |  2 ++
>  kernel/bpf/helpers.c     | 47 ++++++++++++++++++++++++++++++++++++++++
>  kernel/trace/bpf_trace.c | 10 +++++----
>  3 files changed, 55 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index b4825d3cdb29..129c5a7c5982 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);
> +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..ddd1a5a81652 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.
> + */
> +void *__bpf_dynptr_data(const struct bpf_dynptr_kern *ptr, u32 len)

If it's read-only, then this should return `const void *`?

> +{
> +       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 __bpf_dynptr_data(ptr, len);

and then here we can cast to (void *) because we checked is_rdonly
above, I think it would be ok to do that

> +}
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index df697c74d519..bfe6fb83e8d0 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1378,6 +1378,7 @@ __bpf_kfunc int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
>                                struct bpf_dynptr_kern *sig_ptr,
>                                struct bpf_key *trusted_keyring)
>  {
> +       void *data, *sig;
>         int ret;
>
>         if (trusted_keyring->has_ref) {
> @@ -1394,10 +1395,11 @@ __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 = __bpf_dynptr_data(data_ptr, __bpf_dynptr_size(data_ptr));
> +       sig = __bpf_dynptr_data(sig_ptr, __bpf_dynptr_size(sig_ptr));
> +
> +       return verify_pkcs7_signature(data, __bpf_dynptr_size(data_ptr),
> +                                     sig, __bpf_dynptr_size(sig_ptr),
>                                       trusted_keyring->key,
>                                       VERIFYING_UNSPECIFIED_SIGNATURE, NULL,
>                                       NULL);
> --
> 2.34.1
>

Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index b4825d3cdb29..129c5a7c5982 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);
+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..ddd1a5a81652 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.
+ */
+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 __bpf_dynptr_data(ptr, len);
+}
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index df697c74d519..bfe6fb83e8d0 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1378,6 +1378,7 @@  __bpf_kfunc int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
 			       struct bpf_dynptr_kern *sig_ptr,
 			       struct bpf_key *trusted_keyring)
 {
+	void *data, *sig;
 	int ret;
 
 	if (trusted_keyring->has_ref) {
@@ -1394,10 +1395,11 @@  __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 = __bpf_dynptr_data(data_ptr, __bpf_dynptr_size(data_ptr));
+	sig = __bpf_dynptr_data(sig_ptr, __bpf_dynptr_size(sig_ptr));
+
+	return verify_pkcs7_signature(data, __bpf_dynptr_size(data_ptr),
+				      sig, __bpf_dynptr_size(sig_ptr),
 				      trusted_keyring->key,
 				      VERIFYING_UNSPECIFIED_SIGNATURE, NULL,
 				      NULL);