fix luop crash: use buffer for APN that remains valid

In osmo_gsup_configure_wildcard_apn(), do not compose APN into a local buffer
that becomes invalid as soon as the function exits. Instead, use a caller
provided buf.

Fixes OS#3231 crash:

  ==20030==ERROR: AddressSanitizer: stack-buffer-underflow on address 0x7fffffffd9c0 at pc 0x7ffff6e9b6c2 bp 0x7fffffffd900 sp 0x7fffffffd0b0
  READ of size 2 at 0x7fffffffd9c0 thread T0
      #0 0x7ffff6e9b6c1  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0x766c1)
      #1 0x7ffff6314419 in tlv_put ../../../../src/libosmocore/include/osmocom/gsm/tlv.h:107
      #2 0x7ffff6314419 in msgb_tlv_put ../../../../src/libosmocore/include/osmocom/gsm/tlv.h:299
      #3 0x7ffff6314419 in encode_pdp_info ../../../../src/libosmocore/src/gsm/gsup.c:419
      #4 0x7ffff6314419 in osmo_gsup_encode ../../../../src/libosmocore/src/gsm/gsup.c:535
      #5 0x555555580016 in _luop_tx_gsup ../../../src/osmo-hlr/src/luop.c:54
      #6 0x5555555809d8 in lu_op_tx_insert_subscr_data ../../../src/osmo-hlr/src/luop.c:264
      #7 0x55555558b356 in rx_upd_loc_req ../../../src/osmo-hlr/src/hlr.c:306
      #8 0x55555558b356 in read_cb ../../../src/osmo-hlr/src/hlr.c:365
      #9 0x555555586671 in osmo_gsup_server_read_cb ../../../src/osmo-hlr/src/gsup_server.c:105
      #10 0x7ffff5b35911 in ipa_server_conn_read ../../../src/libosmo-abis/src/input/ipa.c:356
      #11 0x7ffff5b35911 in ipa_server_conn_cb ../../../src/libosmo-abis/src/input/ipa.c:387
      #12 0x7ffff5e5541f in osmo_fd_disp_fds ../../../src/libosmocore/src/select.c:216
      #13 0x7ffff5e5541f in osmo_select_main ../../../src/libosmocore/src/select.c:256
      #14 0x5555555791b6 in main ../../../src/osmo-hlr/src/hlr.c:600
      #15 0x7ffff4707a86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21a86)
      #16 0x555555579679 in _start (/usr/local/bin/osmo-hlr+0x25679)

  Address 0x7fffffffd9c0 is located in stack of thread T0 at offset 16 in frame
      #0 0x7ffff63131ff in osmo_gsup_encode ../../../../src/libosmocore/src/gsm/gsup.c:481

    This frame has 1 object(s):
      [32, 64) 'bcd_buf' <== Memory access at offset 16 underflows this variable

Related: OS#3231
Change-Id: I83d9ef2868bbb01e3f1ddb7920fe735aca172b15

4 files changed, 15 insertions, 7 deletions

diff --git a/src/gsup_server.c b/src/gsup_server.c
index 24ba738..03a6f56 100644
--- a/src/gsup_server.c
+++ b/src/gsup_server.c
@@ -335,16 +335,19 @@ void osmo_gsup_server_destroy(struct osmo_gsup_server *gsups)
 	talloc_free(gsups);
 }
 
-void osmo_gsup_configure_wildcard_apn(struct osmo_gsup_message *gsup)
+/* Set GSUP message's pdp_infos[0] to a wildcard APN.
+ * Use the provided apn_buf to store the produced APN data. This must remain valid until
+ * osmo_gsup_encode() is done. */
+void osmo_gsup_configure_wildcard_apn(struct osmo_gsup_message *gsup,
+				      uint8_t *apn_buf, size_t apn_buf_size)
 {
 	int l;
-	uint8_t apn[APN_MAXLEN];
 
-	l = osmo_apn_from_str(apn, sizeof(apn), "*");
+	l = osmo_apn_from_str(apn_buf, apn_buf_size, "*");
 	if (l <= 0)
 		return;
 
-	gsup->pdp_infos[0].apn_enc = apn;
+	gsup->pdp_infos[0].apn_enc = apn_buf;
 	gsup->pdp_infos[0].apn_enc_len = l;
 	gsup->pdp_infos[0].have_info = 1;
 	gsup->num_pdp_infos = 1;
diff --git a/src/gsup_server.h b/src/gsup_server.h
index 3d36bff..b52b783 100644
--- a/src/gsup_server.h
+++ b/src/gsup_server.h
@@ -53,4 +53,5 @@ struct osmo_gsup_server *osmo_gsup_server_create(void *ctx,
 
 void osmo_gsup_server_destroy(struct osmo_gsup_server *gsups);
 
-void osmo_gsup_configure_wildcard_apn(struct osmo_gsup_message *gsup);
+void osmo_gsup_configure_wildcard_apn(struct osmo_gsup_message *gsup,
+				      uint8_t *apn_buf, size_t apn_buf_size);
diff --git a/src/hlr.c b/src/hlr.c
index 195e5d2..cab34f0 100644
--- a/src/hlr.c
+++ b/src/hlr.c
@@ -32,6 +32,7 @@
 #include <osmocom/vty/telnet_interface.h>
 #include <osmocom/vty/ports.h>
 #include <osmocom/ctrl/control_vty.h>
+#include <osmocom/gsm/apn.h>
 
 #include "db.h"
 #include "hlr.h"
@@ -67,6 +68,7 @@ osmo_hlr_subscriber_update_notify(struct hlr_subscriber *subscr)
 		uint8_t *peer;
 		int peer_len;
 		uint8_t msisdn_enc[43]; /* TODO use constant; TS 24.008 10.5.4.7 */
+		uint8_t apn[APN_MAXLEN];
 		int len;
 		struct msgb *msg_out;
 
@@ -96,7 +98,7 @@ osmo_hlr_subscriber_update_notify(struct hlr_subscriber *subscr)
 
 			/* FIXME: PDP infos - use more fine-grained access control
 			   instead of wildcard APN */
-			osmo_gsup_configure_wildcard_apn(&gsup);
+			osmo_gsup_configure_wildcard_apn(&gsup, apn, sizeof(apn));
 		} else if (co->supports_cs) {
 			gsup.cn_domain = OSMO_GSUP_CN_DOMAIN_CS;
 		} else {
diff --git a/src/luop.c b/src/luop.c
index 7150b64..54c3884 100644
--- a/src/luop.c
+++ b/src/luop.c
@@ -27,6 +27,7 @@
 #include <osmocom/core/logging.h>
 #include <osmocom/gsm/gsm48_ie.h>
 #include <osmocom/gsm/gsup.h>
+#include <osmocom/gsm/apn.h>
 
 #include "gsup_server.h"
 #include "gsup_router.h"
@@ -233,6 +234,7 @@ void lu_op_tx_insert_subscr_data(struct lu_operation *luop)
 {
 	struct osmo_gsup_message gsup;
 	uint8_t msisdn_enc[43]; /* TODO use constant; TS 24.008 10.5.4.7 */
+	uint8_t apn[APN_MAXLEN];
 	int l;
 
 	OSMO_ASSERT(luop->state == LU_S_LU_RECEIVED ||
@@ -257,7 +259,7 @@ void lu_op_tx_insert_subscr_data(struct lu_operation *luop)
 	if (luop->is_ps) {
 		/* FIXME: PDP infos - use more fine-grained access control
 		   instead of wildcard APN */
-		osmo_gsup_configure_wildcard_apn(&gsup);
+		osmo_gsup_configure_wildcard_apn(&gsup, apn, sizeof(apn));
 	}
 
 	/* Send ISD to new VLR/SGSN */