Deprecate ipa_ccm_idtag_parse() with ipa_ccm_id_{get,resp}_parse()

In the past, the function ipa_ccm_idtag_parse() was used to parse
the payload of IPA CCM ID RESP packets.  However, the function was
based on a possible misunderstanding of the message encoding, and
callers actually counted the first (upper) length nibble as part
of the header and passed a pointer to the second
(lower) length nibble of the first TLV into this function.  As such,
it was unfixable, and had to be replaced with a new function called
ipa_ccm_id_resp_parse().  At the same time, we also add
ipa_ccm_id_get_parse() to parse the slightly different format of
the IPA CCM ID GET payload.

We can never be 100% sure what is "correct", as our understanding
of the protocol is entirely based on protocol analysis, without any
official documentation available.

This patch also introduces unit test coverage for both of the new
functions.

Revert "ipa: Add libosmogsm.map entry for ipa_ccm_idtag_parse_off"
This reverts commit 7f31c90b80c08fbfe2d84d70d397402fdb38b94c.

Revert "ipa: Properly parse LV stream of a ID_GET request"
This reverts commit f558ed4bb9c0f00997b8f97c2b251a574c1a64c4.

It introduced a function/behavior that was not originally intended:
The parse of IPA CCM ID GET (8bit length followed by 1 byte tag
and variable-length payload) instead of the IPA CCM ID RESP (16bit
length followed by 1 byte tag and variable-length payload).

Change-Id: I1834d90fbcdbfcb05f5b8cfe39bfe9543737ef8f

2 files changed, 77 insertions, 9 deletions

diff --git a/src/gsm/ipa.c b/src/gsm/ipa.c
index aecde831..3c7c300b 100644
--- a/src/gsm/ipa.c
+++ b/src/gsm/ipa.c
@@ -100,14 +100,47 @@ const char *ipa_ccm_idtag_name(uint8_t tag)
 
 int ipa_ccm_idtag_parse(struct tlv_parsed *dec, unsigned char *buf, int len)
 {
-	return ipa_ccm_idtag_parse_off(dec, buf, len, 0);
+	uint8_t t_len;
+	uint8_t t_tag;
+	uint8_t *cur = buf;
+
+	memset(dec, 0, sizeof(*dec));
+
+	while (len >= 2) {
+		len -= 2;
+		t_len = *cur++;
+		t_tag = *cur++;
+
+		if (t_len > len + 1) {
+			LOGP(DLMI, LOGL_ERROR, "The tag does not fit: %d > %d\n", t_len, len + 1);
+			return -EINVAL;
+		}
+
+		DEBUGPC(DLMI, "%s='%s' ", ipa_ccm_idtag_name(t_tag), cur);
+
+		dec->lv[t_tag].len = t_len;
+		dec->lv[t_tag].val = cur;
+
+		cur += t_len;
+		len -= t_len;
+	}
+	return 0;
 }
 
-int ipa_ccm_idtag_parse_off(struct tlv_parsed *dec, unsigned char *buf, int len, const int len_offset)
+/*! Parse the payload part of an IPA CCM ID GET, return \ref tlv_parsed format.
+ *  The odd payload format of those messages is structured as follows:
+ *   * 8bit length value (length of payload *and tag*)
+ *   * 8bit tag value
+ *   * optional, variable-length payload
+ *  \param[out] dec Caller-provided/allocated output structure for parsed payload
+ *  \param[in] buf Buffer containing the payload (excluding 1 byte msg_type) of the message
+ *  \param[in] len Length of \a buf in octets
+ *  \returns 0 on success; negative on error */
+int ipa_ccm_id_get_parse(struct tlv_parsed *dec, const uint8_t *buf, unsigned int len)
 {
 	uint8_t t_len;
 	uint8_t t_tag;
-	uint8_t *cur = buf;
+	const uint8_t *cur = buf;
 
 	memset(dec, 0, sizeof(*dec));
 
@@ -116,11 +149,45 @@ int ipa_ccm_idtag_parse_off(struct tlv_parsed *dec, unsigned char *buf, int len,
 		t_len = *cur++;
 		t_tag = *cur++;
 
-		if (t_len < len_offset) {
-			LOGP(DLMI, LOGL_ERROR, "minimal offset not included: %d < %d\n", t_len, len_offset);
+		if (t_len > len + 1) {
+			LOGP(DLMI, LOGL_ERROR, "The tag does not fit: %d > %d\n", t_len, len + 1);
 			return -EINVAL;
 		}
 
+		DEBUGPC(DLMI, "%s='%s' ", ipa_ccm_idtag_name(t_tag), cur);
+
+		dec->lv[t_tag].len = t_len-1;
+		dec->lv[t_tag].val = cur;
+
+		cur += t_len-1;
+		len -= t_len-1;
+	}
+	return 0;
+}
+
+/*! Parse the payload part of an IPA CCM ID RESP, return \ref tlv_parsed format.
+ *  The odd payload format of those messages is structured as follows:
+ *   * 16bit length value (length of payload *and tag*)
+ *   * 8bit tag value
+ *   * optional, variable-length payload
+ *  \param[out] dec Caller-provided/allocated output structure for parsed payload
+ *  \param[in] buf Buffer containing the payload (excluding 1 byte msg_type) of the message
+ *  \param[in] len Length of \a buf in octets
+ *  \returns 0 on success; negative on error */
+int ipa_ccm_id_resp_parse(struct tlv_parsed *dec, const uint8_t *buf, unsigned int len)
+{
+	uint8_t t_len;
+	uint8_t t_tag;
+	const uint8_t *cur = buf;
+
+	memset(dec, 0, sizeof(*dec));
+
+	while (len >= 3) {
+		len -= 3;
+		t_len = *cur++ << 8;
+		t_len += *cur++;
+		t_tag = *cur++;
+
 		if (t_len > len + 1) {
 			LOGP(DLMI, LOGL_ERROR, "The tag does not fit: %d > %d\n", t_len, len + 1);
 			return -EINVAL;
@@ -128,11 +195,11 @@ int ipa_ccm_idtag_parse_off(struct tlv_parsed *dec, unsigned char *buf, int len,
 
 		DEBUGPC(DLMI, "%s='%s' ", ipa_ccm_idtag_name(t_tag), cur);
 
-		dec->lv[t_tag].len = t_len - len_offset;
+		dec->lv[t_tag].len = t_len-1;
 		dec->lv[t_tag].val = cur;
 
-		cur += t_len - len_offset;
-		len -= t_len - len_offset;
+		cur += t_len-1;
+		len -= t_len-1;
 	}
 	return 0;
 }
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index bc9ed528..a1d342aa 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -461,7 +461,8 @@ ipa_ccm_send_pong;
 ipa_ccm_tlv_to_unitdata;
 ipa_ccm_idtag_name;
 ipa_ccm_idtag_parse;
-ipa_ccm_idtag_parse_off;
+ipa_ccm_id_get_parse;
+ipa_ccm_id_resp_parse;
 ipa_ccm_make_id_resp;
 ipa_ccm_make_id_resp_from_req;
 ipa_msg_alloc;