lib/util/asn1: add asn1_peek_tag_needed_size() and asn1_peek_full_tag()

We need a way to ask for the length of a tag without having the full
buffer yet.

metze

diff --git a/lib/util/asn1.c b/lib/util/asn1.c
index 8f30cfe2c677cfe982636607466ad63f7c77631b..c4923343e259068e507021d182507787693282bf 100644 (file)
--- a/lib/util/asn1.c
+++ b/lib/util/asn1.c
@@ -489,6 +489,65 @@ bool asn1_peek_tag(struct asn1_data *data, uint8_t tag)
        return (b == tag);
 }
 
+/*
+ * just get the needed size the tag would consume
+ */
+bool asn1_peek_tag_needed_size(struct asn1_data *data, uint8_t tag, size_t *size)
+{
+       off_t start_ofs = data->ofs;
+       uint8_t b;
+       size_t taglen = 0;
+
+       if (data->has_error) {
+               return false;
+       }
+
+       if (!asn1_read_uint8(data, &b)) {
+               data->ofs = start_ofs;
+               data->has_error = false;
+               return false;
+       }
+
+       if (b != tag) {
+               data->ofs = start_ofs;
+               data->has_error = false;
+               return false;
+       }
+
+       if (!asn1_read_uint8(data, &b)) {
+               data->ofs = start_ofs;
+               data->has_error = false;
+               return false;
+       }
+
+       if (b & 0x80) {
+               int n = b & 0x7f;
+               if (!asn1_read_uint8(data, &b)) {
+                       data->ofs = start_ofs;
+                       data->has_error = false;
+                       return false;
+               }
+               taglen = b;
+               while (n > 1) {
+                       if (!asn1_read_uint8(data, &b)) {
+                               data->ofs = start_ofs;
+                               data->has_error = false;
+                               return false;
+                       }
+                       taglen = (taglen << 8) | b;
+                       n--;
+               }
+       } else {
+               taglen = b;
+       }
+
+       *size = (data->ofs - start_ofs) + taglen;
+
+       data->ofs = start_ofs;
+       data->has_error = false;
+       return true;
+}
+
 /* start reading a nested asn1 structure */
 bool asn1_start_tag(struct asn1_data *data, uint8_t tag)
 {
@@ -943,6 +1002,30 @@ NTSTATUS asn1_full_tag(DATA_BLOB blob, uint8_t tag, size_t *packet_size)
 
        if (size > blob.length) {
                return STATUS_MORE_ENTRIES;
+       }
+
+       *packet_size = size;
+       return NT_STATUS_OK;
+}
+
+NTSTATUS asn1_peek_full_tag(DATA_BLOB blob, uint8_t tag, size_t *packet_size)
+{
+       struct asn1_data asn1;
+       uint32_t size;
+       bool ok;
+
+       ZERO_STRUCT(asn1);
+       asn1.data = blob.data;
+       asn1.length = blob.length;
+
+       ok = asn1_peek_tag_needed_size(&asn1, tag, &size);
+       if (!ok) {
+               return STATUS_MORE_ENTRIES;
+       }
+
+       if (size > blob.length) {
+               *packet_size = size;
+               return STATUS_MORE_ENTRIES;
        }               
 
        *packet_size = size;

diff --git a/lib/util/asn1.h b/lib/util/asn1.h
index ded3244bed15ce0b77859111926ef82428940f85..266a9a386bb95ba73bfe318ce61fe1aae3296a9f 100644 (file)
--- a/lib/util/asn1.h
+++ b/lib/util/asn1.h
@@ -79,6 +79,7 @@ bool asn1_peek(struct asn1_data *data, void *p, int len);
 bool asn1_read(struct asn1_data *data, void *p, int len);
 bool asn1_read_uint8(struct asn1_data *data, uint8_t *v);
 bool asn1_peek_uint8(struct asn1_data *data, uint8_t *v);
+bool asn1_peek_tag_needed_size(struct asn1_data *data, uint8_t tag, size_t *size);
 bool asn1_peek_tag(struct asn1_data *data, uint8_t tag);
 bool asn1_start_tag(struct asn1_data *data, uint8_t tag);
 bool asn1_end_tag(struct asn1_data *data);
@@ -100,5 +101,6 @@ bool asn1_write_enumerated(struct asn1_data *data, uint8_t v);
 bool asn1_blob(const struct asn1_data *asn1, DATA_BLOB *blob);
 void asn1_load_nocopy(struct asn1_data *data, uint8_t *buf, size_t len);
 NTSTATUS asn1_full_tag(DATA_BLOB blob, uint8_t tag, size_t *packet_size);
+NTSTATUS asn1_peek_full_tag(DATA_BLOB blob, uint8_t tag, size_t *packet_size);
 
 #endif /* _ASN_1_H */