Change in osmo-bts[master]: measurement.c: fix integer overflow problem

[dexter]

dexter has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-bts/+/20979 )


Change subject: measurement.c: fix integer overflow problem
......................................................................

measurement.c: fix integer overflow problem

The variables num_meas_sub_expect - num_meas_sub must not be subtracted
without prior checking. Depending on the input (which might be
errornous), num_meas_sub might be greater then num_meas_sub_expect. This
eventually leads into odd behavior, which can be difficult to debug.

Change-Id: I381cc637d1c125f279ccf88db114609946fe24fe
Related: OS#4799
---
M src/common/measurement.c
1 file changed, 3 insertions(+), 1 deletion(-)



  git pull ssh://gerrit.osmocom.org:29418/osmo-bts refs/changes/79/20979/1

diff --git a/src/common/measurement.c b/src/common/measurement.c
index d5c3ee0..a388847 100644
--- a/src/common/measurement.c
+++ b/src/common/measurement.c
@@ -642,7 +642,9 @@
 			 * negotiated in AMR, so we can not know if and how many
 			 * SUB frames are missing. */
 			if (lchan->tch_mode != GSM48_CMODE_SPEECH_AMR) {
-				if (num_ul_meas_expect - i <= num_meas_sub_expect - num_meas_sub) {
+				if (num_meas_sub < num_meas_sub_expect
+				    && num_ul_meas_expect - i <=
+				    num_meas_sub_expect - num_meas_sub) {
 					num_meas_sub_subst++;
 					is_sub = true;
 				}

-- 
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Gerrit-Project: osmo-bts
Gerrit-Branch: master
Gerrit-Change-Id: I381cc637d1c125f279ccf88db114609946fe24fe
Gerrit-Change-Number: 20979
Gerrit-PatchSet: 1
Gerrit-Owner: dexter <pmaier at sysmocom.de>
Gerrit-MessageType: newchange
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