[PATCH] osmo-bsc[master]: sysinfo: Fix regression causing missing L2 Pseudo-Length in ...

[Harald Welte]

Review at  https://gerrit.osmocom.org/7220

sysinfo: Fix regression causing missing L2 Pseudo-Length in SI5/SI6

Fixes a regression in the code generating SI5* and SI6 on SACCH,
where the L@ pseudo-length is not part of the 'struct' definition
we have in gsm_04_08.h and hence has to be encoded manually into
the first byte of the SI buffer.

We were doing this correctly until April 2017, when the following
patch was merged:

> commit 6f0e50c8337355eb59033903ede9ab6528890835
> Author: Max <msuraev at sysmocom.de>
> Date:   Wed Apr 12 15:30:54 2017 +0200
>
>     Prepare for extended SI2quater support

This patch cacidentially overwrote the l2_plen that was just enoded,
as the 'struct' was no longer pointing to 'output' (si_buf+1), but
now directly to the start of the si_buf.

NOTE: The Wireshark RSL dissector (and more recently also LAPDm)
contain a similar bug, so the SACCH will not be decoded correctly
after applying this patch. Nevertheless, it's correct.

Change-Id: Ie8c907b1317566670aeb68f933ceefd552c17565
Closes: #3059
Related: #2963
---
M src/libbsc/system_information.c
1 file changed, 5 insertions(+), 5 deletions(-)


  git pull ssh://gerrit.osmocom.org:29418/osmo-bsc refs/changes/20/7220/1

diff --git a/src/libbsc/system_information.c b/src/libbsc/system_information.c
index c7c85b0..d99153f 100644
--- a/src/libbsc/system_information.c
+++ b/src/libbsc/system_information.c
@@ -959,7 +959,7 @@
 		break;
 	}
 
-	si5 = (struct gsm48_system_information_type_5 *) GSM_BTS_SI(bts, t);
+	si5 = (struct gsm48_system_information_type_5 *) output;
 
 	/* l2 pseudo length, not part of msg: 18 */
 	si5->rr_protocol_discriminator = GSM48_PDISC_RR;
@@ -995,7 +995,7 @@
 		break;
 	}
 
-	si5b = (struct gsm48_system_information_type_5bis *) GSM_BTS_SI(bts, t);
+	si5b = (struct gsm48_system_information_type_5bis *) output;
 
 	/* l2 pseudo length, not part of msg: 18 */
 	si5b->rr_protocol_discriminator = GSM48_PDISC_RR;
@@ -1009,7 +1009,7 @@
 	if (n) {
 		/* indicate in SI5 and SI5bis: there is an extension */
 		struct gsm48_system_information_type_5 *si5 =
-			(struct gsm48_system_information_type_5 *) GSM_BTS_SI(bts, SYSINFO_TYPE_5);
+			(struct gsm48_system_information_type_5 *) GSM_BTS_SI(bts, SYSINFO_TYPE_5)+1;
 		si5->bcch_frequency_list[0] |= 0x20;
 		si5b->bcch_frequency_list[0] |= 0x20;
 	} else
@@ -1039,7 +1039,7 @@
 		break;
 	}
 
-	si5t = (struct gsm48_system_information_type_5ter *) GSM_BTS_SI(bts, t);
+	si5t = (struct gsm48_system_information_type_5ter *) output;
 
 	/* l2 pseudo length, not part of msg: 18 */
 	si5t->rr_protocol_discriminator = GSM48_PDISC_RR;
@@ -1077,7 +1077,7 @@
 		break;
 	}
 
-	si6 = (struct gsm48_system_information_type_6 *) GSM_BTS_SI(bts, t);
+	si6 = (struct gsm48_system_information_type_6 *) output;
 
 	/* l2 pseudo length, not part of msg: 11 */
 	si6->rr_protocol_discriminator = GSM48_PDISC_RR;

-- 
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Gerrit-MessageType: newchange
Gerrit-Change-Id: Ie8c907b1317566670aeb68f933ceefd552c17565
Gerrit-PatchSet: 1
Gerrit-Project: osmo-bsc
Gerrit-Branch: master
Gerrit-Owner: Harald Welte <laforge at gnumonks.org>