path: root/include/osmocom/sigtran/sccp_sap.h
diff options
authorNeels Hofmeyr <>2019-03-10 04:41:27 +0100
committerNeels Hofmeyr <>2019-04-12 06:27:10 +0200
commitac729eb5a8295d0c1fc2dea3fb0f56413654c13e (patch)
treebb8968730c096a2889fefb536842f731ad5bb4e9 /include/osmocom/sigtran/sccp_sap.h
parent49eea32ab4158b2b80a3862513363f237fb49939 (diff)
add caller-owns-msgb variant osmo_sccp_user_sap_down_nofree()
Add osmo_sccp_user_sap_down_nofree(), which is identical to osmo_sccp_user_sap_down(), but doesn't imply a msgb_free(). To implement that, sccp_sclc_user_sap_down_nofree() with the same msgb semantics is required. Rationale: Avoiding msgb leaks is easiest if the caller retains ownership of the msgb. Take this hypothetical chain where leaks are obviously avoided: void send() { msg = msgb_alloc(); dispatch(msg); msgb_free(msg); } void dispatch(msg) { osmo_fsm_inst_dispatch(fi, msg); } void fi_on_event(fi, data) { if (socket_is_ok) socket_write((struct msgb*)data); } void socket_write(msgb) { if (!ok1) return; if (ok2) { if (!ok3) return; write(sock, msg->data); } } However, if the caller passes ownership down to the msgb consumer, things become nightmarishly complex: void send() { msg = msgb_alloc(); rc = dispatch(msg); /* dispatching event failed? */ if (rc) msgb_free(msg); } int dispatch(msg) { if (osmo_fsm_inst_dispatch(fi, msg)) return -1; if (something_else()) return -1; // <-- double free! } void fi_on_event(fi, data) { if (socket_is_ok) { socket_write((struct msgb*)data); else /* socket didn't consume? */ msgb_free(data); } int socket_write(msgb) { if (!ok1) return -1; // <-- leak! if (ok2) { if (!ok3) goto out; write(sock, msg->data); } out: msgb_free(msg); return -2; } If any link in this call chain fails to be aware of the importance to return a failed RC or to free a msgb if the chain is broken, or to not return a failed RC if the msgb is consumed, we have a hidden msgb leak or double free. This is the case with osmo_sccp_user_sap_down(). In new osmo-msc, passing data through various FSM instances, there is high potential for leak/double-free bugs. A very large brain is required to track down every msgb path. osmo_sccp_user_sap_down_nofree() makes this problem trivial to solve even for humans. Change-Id: Ic818efa78b90f727e1a94c18b60d9a306644f340
Diffstat (limited to 'include/osmocom/sigtran/sccp_sap.h')
1 files changed, 1 insertions, 0 deletions
diff --git a/include/osmocom/sigtran/sccp_sap.h b/include/osmocom/sigtran/sccp_sap.h
index 84d762c..f64b7aa 100644
--- a/include/osmocom/sigtran/sccp_sap.h
+++ b/include/osmocom/sigtran/sccp_sap.h
@@ -263,6 +263,7 @@ osmo_sccp_user_bind(struct osmo_sccp_instance *inst, const char *name,
osmo_prim_cb prim_cb, uint16_t ssn);
int osmo_sccp_user_sap_down(struct osmo_sccp_user *scu, struct osmo_prim_hdr *oph);
+int osmo_sccp_user_sap_down_nofree(struct osmo_sccp_user *scu, struct osmo_prim_hdr *oph);
struct osmo_ss7_instance *
osmo_sccp_addr_by_name(struct osmo_sccp_addr *dest_addr,