Change in libosmocore[master]: ns2: Avoid use-after-free when SGSN-side non-persistent SNS-NSE fails

[laforge]

laforge has submitted this change. ( https://gerrit.osmocom.org/c/libosmocore/+/26199 )

Change subject: ns2: Avoid use-after-free when SGSN-side non-persistent SNS-NSE fails
......................................................................

ns2: Avoid use-after-free when SGSN-side non-persistent SNS-NSE fails

alive_timeout_handler() changes the state to RECOVERING which calls
ns2_st_alive_onenter()->ns2_nse_notify_unblocked(unblocked=false)->
ns2_sns_notify_alive(unblocked=false)

When all (signalling) NSVCs have failed and gss->role is SGSN and not
persistent sns_failed() calls gprs_ns2_free_nse() which talloc_free()s
the nse before returning.

The next line in ns2_nse_notify_unblocked() tries to read nse->alive which then causes the
use-after-free.

Change-Id: I0486a77fd3e21fd3904bd19e4e0225ffbf654935
Related: OS#5302
---
M src/gb/gprs_ns2.c
1 file changed, 6 insertions(+), 1 deletion(-)

Approvals:
  Jenkins Builder: Verified
  pespin: Looks good to me, but someone else must approve
  osmith: Looks good to me, but someone else must approve
  laforge: Looks good to me, approved



diff --git a/src/gb/gprs_ns2.c b/src/gb/gprs_ns2.c
index 3bb04ae..02d2266 100644
--- a/src/gb/gprs_ns2.c
+++ b/src/gb/gprs_ns2.c
@@ -1392,11 +1392,16 @@
 void ns2_nse_notify_unblocked(struct gprs_ns2_vc *nsvc, bool unblocked)
 {
 	struct gprs_ns2_nse *nse = nsvc->nse;
+	struct gprs_ns2_inst *nsi = nse->nsi;
+	uint16_t nsei = nse->nsei;
 
 	ns2_nse_data_sum(nse);
 	ns2_sns_notify_alive(nse, nsvc, unblocked);
 
-	if (unblocked == nse->alive)
+	/* NSE could have been freed, try to get it again */
+	nse = gprs_ns2_nse_by_nsei(nsi, nsei);
+
+	if (!nse || unblocked == nse->alive)
 		return;
 
 	/* wait until both data_weight and sig_weight are != 0 before declaring NSE as alive */

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Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Change-Id: I0486a77fd3e21fd3904bd19e4e0225ffbf654935
Gerrit-Change-Number: 26199
Gerrit-PatchSet: 3
Gerrit-Owner: daniel <dwillmann at sysmocom.de>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-Reviewer: lynxis lazus <lynxis at fe80.eu>
Gerrit-Reviewer: osmith <osmith at sysmocom.de>
Gerrit-Reviewer: pespin <pespin at sysmocom.de>
Gerrit-MessageType: merged
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