bsc: Fix use-after-free on OML NM messages from the BTS
Currently the sign_link pointer is dereferenced after a call to
osmo_signal_dispatch, which can indirectly call
e1inp_sign_link_destroy. If that happens, accessing *sign_link is
illegal and can lead to a segmentation violation.
Since only the bts pointer is needed from sign_link after the call to
osmo_signal_dispatch, this patch changes abis_nm_rcvmsg_fom to save
that pointer to a local variable earlier.
Addresses:
<0019> input/ipa.c:250 accept()ed new link from 192.168.1.101 to port 3002
SET ATTR NACK CAUSE=Message cannot be performed
<0005> bsc_init.c:52 Got a NACK going to drop the OML links.
<001b> bsc_init.c:319 Lost some E1 TEI link: 1 0xb351a830
=================================================================
==13198== ERROR: AddressSanitizer: heap-use-after-free on address 0xb5d1bc70 at pc 0x80a6e3d bp 0xbfbb33d8 sp 0xbfbb33cc
Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/libbsc/abis_nm.c b/openbsc/src/libbsc/abis_nm.c
index 3bf55ec..c05e2f9 100644
--- a/openbsc/src/libbsc/abis_nm.c
+++ b/openbsc/src/libbsc/abis_nm.c
@@ -565,6 +565,8 @@
struct abis_om_fom_hdr *foh = msgb_l3(mb);
struct e1inp_sign_link *sign_link = mb->dst;
uint8_t mt = foh->msg_type;
+ /* sign_link might get deleted via osmo_signal_dispatch -> save bts */
+ struct gsm_bts *bts = sign_link->trx->bts;
int ret = 0;
/* check for unsolicited message */
@@ -582,7 +584,7 @@
DEBUGPC(DNM, "%s NACK ", abis_nm_nack_name(mt));
- abis_nm_tlv_parse(&tp, sign_link->trx->bts, foh->data, oh->length-sizeof(*foh));
+ abis_nm_tlv_parse(&tp, bts, foh->data, oh->length-sizeof(*foh));
if (TLVP_PRESENT(&tp, NM_ATT_NACK_CAUSES))
DEBUGPC(DNM, "CAUSE=%s\n",
abis_nm_nack_cause_name(*TLVP_VAL(&tp, NM_ATT_NACK_CAUSES)));
@@ -591,9 +593,9 @@
nack_data.msg = mb;
nack_data.mt = mt;
- nack_data.bts = sign_link->trx->bts;
+ nack_data.bts = bts;
osmo_signal_dispatch(SS_NM, S_NM_NACK, &nack_data);
- abis_nm_queue_send_next(sign_link->trx->bts);
+ abis_nm_queue_send_next(bts);
return 0;
}
#if 0
@@ -636,7 +638,7 @@
break;
}
- abis_nm_queue_send_next(sign_link->trx->bts);
+ abis_nm_queue_send_next(bts);
return ret;
}