[MERGED] osmo-msc[master]: msc_mgcp: to not access higher layers after release

[Harald Welte]

Harald Welte has submitted this change and it was merged.

Change subject: msc_mgcp: to not access higher layers after release
......................................................................


msc_mgcp: to not access higher layers after release

The higher layers (gsm_04_08.c) are informed errors occur. But it
is not checked if the call was already released. If an error occurs
after the call control stack calls msc_mgcp_call_release() then
the higher layers might already have cleaned up and the code
accesses memory that is already freed (trans)

- fix use after free by guarding the call to mncc_tx_to_cc()

Change-Id: I78f1b6a9149488a4ad3f120c1e190a83c07d4b89
Related OS#2881
Related OS#2882
---
M src/libmsc/msc_mgcp.c
1 file changed, 9 insertions(+), 4 deletions(-)

Approvals:
  Harald Welte: Looks good to me, approved
  Jenkins Builder: Verified



diff --git a/src/libmsc/msc_mgcp.c b/src/libmsc/msc_mgcp.c
index 8e874d8..5c615a9 100644
--- a/src/libmsc/msc_mgcp.c
+++ b/src/libmsc/msc_mgcp.c
@@ -197,10 +197,15 @@
 		osmo_fsm_inst_dispatch(fi, EV_TEARDOWN_ERROR, mgcp_ctx);
 	}
 
-	/* Request the higher layers to release the call */
-	mncc_set_cause(&mncc, GSM48_CAUSE_LOC_TRANS_NET,
-		       GSM48_CC_CAUSE_RESOURCE_UNAVAIL);
-	mncc_tx_to_cc(mgcp_ctx->trans->net, MNCC_REL_REQ, &mncc);
+	/* Request the higher layers (gsm_04_08.c) to release the call. If the
+	 * problem occured after msc_mgcp_call_release() was calls, remain
+	 * silent because we already got informed and the higher layers might
+	 * already freed their context information (trans). */
+	if (!mgcp_ctx->free_ctx) {
+		mncc_set_cause(&mncc, GSM48_CAUSE_LOC_TRANS_NET,
+			       GSM48_CC_CAUSE_RESOURCE_UNAVAIL);
+		mncc_tx_to_cc(mgcp_ctx->trans->net, MNCC_REL_REQ, &mncc);
+	}
 }
 
 /* Timer callback to shut down in case of connectivity problems */

-- 
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Gerrit-MessageType: merged
Gerrit-Change-Id: I78f1b6a9149488a4ad3f120c1e190a83c07d4b89
Gerrit-PatchSet: 2
Gerrit-Project: osmo-msc
Gerrit-Branch: master
Gerrit-Owner: dexter <pmaier at sysmocom.de>
Gerrit-Reviewer: Harald Welte <laforge at gnumonks.org>
Gerrit-Reviewer: Jenkins Builder