[PATCH] libosmocore[master]: gsm0480: drop messages with incorrect data length

[Vadim Yanitskiy]

Review at  https://gerrit.osmocom.org/7630

gsm0480: drop messages with incorrect data length

If either an INVOKE, either a RETURN_RESULT component has the
data with incorrect length (see Annex A, 3GPP TS 04.80), the
whole message is probably incorrect.

Let's drop such messages instead of silent truncation.

Change-Id: I2a169b0b84aa26ea2521edd55ff005c27ae6d808
---
M src/gsm/gsm0480.c
1 file changed, 12 insertions(+), 9 deletions(-)


  git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/30/7630/1

diff --git a/src/gsm/gsm0480.c b/src/gsm/gsm0480.c
index 38082b3..dd58249 100644
--- a/src/gsm/gsm0480.c
+++ b/src/gsm/gsm0480.c
@@ -552,8 +552,12 @@
 	if (num_chars > length - 2)
 		return 0;
 
-	if (num_chars > GSM0480_USSD_OCTET_STRING_LEN)
-		num_chars = GSM0480_USSD_OCTET_STRING_LEN;
+	/* Drop messages with incorrect length */
+	if (num_chars > GSM0480_USSD_OCTET_STRING_LEN) {
+		LOGP(0, LOGL_ERROR, "Incorrect USS_DATA data length=%u, "
+			"dropping message", num_chars);
+		return 0;
+	}
 
 	memcpy(req->ussd_text, uss_req_data + 2, num_chars);
 
@@ -588,9 +592,12 @@
 	/* Get the amount of bytes */
 	num_chars = uss_req_data[6];
 
-	/* Prevent a mobile-originated buffer-overrun! */
-	if (num_chars > GSM0480_USSD_OCTET_STRING_LEN)
-		num_chars = GSM0480_USSD_OCTET_STRING_LEN;
+	/* Drop messages with incorrect length */
+	if (num_chars > GSM0480_USSD_OCTET_STRING_LEN) {
+		LOGP(0, LOGL_ERROR, "Incorrect USS_REQ data length=%u, "
+			"dropping message", num_chars);
+		return 0;
+	}
 
 	/* Copy the data 'as is' */
 	memcpy(req->ussd_data, uss_req_data + 7, num_chars);
@@ -605,10 +612,6 @@
 	if (dcs == 0x0F) {
 		/* Calculate the amount of 7-bit characters */
 		num_chars = (num_chars * 8) / 7;
-
-		/* Prevent a mobile-originated buffer-overrun! */
-		if (num_chars > GSM0480_USSD_7BIT_STRING_LEN)
-			num_chars = GSM0480_USSD_7BIT_STRING_LEN;
 
 		gsm_7bit_decode_n_ussd((char *)req->ussd_text,
 			sizeof(req->ussd_text), &(uss_req_data[7]), num_chars);

-- 
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I2a169b0b84aa26ea2521edd55ff005c27ae6d808
Gerrit-PatchSet: 1
Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Owner: Vadim Yanitskiy <axilirator at gmail.com>