pespin has uploaded this change for review. (
https://gerrit.osmocom.org/c/osmo-bsc/+/42010?usp=email )
Change subject: assignment_fsm: Fix use-after-free of lchan->conn
......................................................................
assignment_fsm: Fix use-after-free of lchan->conn
Scenario:
* A DYNAMIC/OSMOCOM TS in PDCH mode is selected to be used for TCH/F,
hence the TS is being switched to TCH/F: RF Channel Release is being
transmitted and waiting to receive RF Channel release ACK. Hence,
lchan is in state LCHAN_ST_WAIT_TS_READY, and there's a conn with an
assignment FSM pointing to it in conn->assignment.new_lchan.
lchan->conn also points to the related conn.
* The BSSMAP SCCP link goes down (link lost), which will terminate the
conn->fi of all conns related to the MSC peer going down.
During that teardown, first gscon_pre_term()->gscon_release_lchans()->
assignment_reset() is called, which sets
conn->assignment.new_lchan=NULL and calls lchan_release(). This path
leaves conn->assignment.new_lchan->conn untouched!
* Later in the call path, when finally the bsc_subscr is put() to 0
references and associated lchan gets its lchan_forget_conn() called,
it will access lchan->conn which was not freed in the previous step
mentioned above during assignment_reset().
This patch fixes the issue by adding a lchan_forget_conn() after the
lchan_release() in assignment_reset(), to make sure the conn is no
longer user by the lchan afterwards.
Related: OS#6936
Change-Id: Ifbb9a61cd8a40d953ef5c2b52f9be9ef0dffefa4
---
M src/osmo-bsc/assignment_fsm.c
1 file changed, 1 insertion(+), 0 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-bsc refs/changes/10/42010/1
diff --git a/src/osmo-bsc/assignment_fsm.c b/src/osmo-bsc/assignment_fsm.c
index f0a2781..e5392f6 100644
--- a/src/osmo-bsc/assignment_fsm.c
+++ b/src/osmo-bsc/assignment_fsm.c
@@ -127,6 +127,7 @@
struct gsm_lchan *lchan = conn->assignment.new_lchan;
conn->assignment.new_lchan = NULL;
lchan_release(lchan, false, true, RSL_ERR_EQUIPMENT_FAIL, NULL);
+ lchan_forget_conn(lchan);
}
if (conn->assignment.created_ci_for_msc) {
--
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Gerrit-MessageType: newchange
Gerrit-Project: osmo-bsc
Gerrit-Branch: master
Gerrit-Change-Id: Ifbb9a61cd8a40d953ef5c2b52f9be9ef0dffefa4
Gerrit-Change-Number: 42010
Gerrit-PatchSet: 1
Gerrit-Owner: pespin <[email protected]>
