cellular-infrastructure
/
osmo-bsc
mirror of https://gerrit.osmocom.org/osmo-bsc
9
0
Fork 0
Code Issues Releases Wiki Activity

gsm48_parse_meas_rep(): set num_cell=0 if no neighbor cells are reported 

Set mr->num_cell to 0 if the bits reflect 0x7, which means that no neighbor
cell measurements are enclosed in the report.

The code in gsm48_parse_meas_rep() acknowledges that, but nevertheless left
num_cell == 7, and evaluating code commonly runs into the mistake of assuming
that actually seven neighbors are being reported on, like:

 MEASUREMENT REPORT
   0: arfcn=0 bsic=0 neigh_idx=0 rxlev=0 flags=0
   1: arfcn=0 bsic=0 neigh_idx=0 rxlev=0 flags=0
   2: arfcn=0 bsic=0 neigh_idx=0 rxlev=0 flags=0
   3: arfcn=0 bsic=0 neigh_idx=0 rxlev=0 flags=0
   4: arfcn=0 bsic=0 neigh_idx=0 rxlev=0 flags=0
   5: arfcn=0 bsic=0 neigh_idx=0 rxlev=0 flags=0
   6: arfcn=0 bsic=0 neigh_idx=0 rxlev=0 flags=0

There are only up to 6 slots for neighbors, the above listing actually printed
7, because num_cell == 7, which is a potential segfault.  (sometimes it printed
uninitialized values instead of 0)

We could fix all meas rep consumers to know what num_cell == 7 means, but
instead setting it to 0 trivially fixes all of them.

Change-Id: Ie12210660a04f2d664ddc92e7ad7fc39ee474180
This commit is contained in:
Neels Hofmeyr 2018-03-08 03:17:48 +01:00
parent f93970b167
commit f0141b95cd
1 changed files with 4 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
src/libbsc/gsm_04_08_utils.c
View File

@ -551,8 +551,11 @@ int gsm48_parse_meas_rep(struct gsm_meas_rep *rep, struct msgb *msg)
rep->dl.sub.rx_qual = (data[2] >> 1) & 0x7;
rep->num_cell = ((data[3] >> 6) & 0x3) | ((data[2] & 0x01) << 2);
if (rep->num_cell < 1 || rep->num_cell > 6)
if (rep->num_cell < 1 || rep->num_cell > 6) {
/* There are no neighbor cell reports present. */
rep->num_cell = 0;
return 0;
}
/* an encoding nightmare in perfection */
mrc = &rep->cell[0];