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

[Song Liu <song@kernel.org>]

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 | 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)
+{
+	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);
-- 
2.34.1