[PATCH 2/3] smpp_smsc: Check that the size is large enough to hold actual data

[Daniel Willmann]

From: Daniel Willmann <dwillmann at sysmocom.de>

The first 4 bytes are the length including the length field. For
length < 4 the subsequent msgb_put(msg, sizeof(uint32_t)) will fail,
resulting in an abort. The code also expects (in smpp_msgb_cmdid()) the
existence of 4 more bytes for the SMPP command ID.

This patch checks that the length received is large enough to hold all
8 bytes in the msgb and drops the connection if that's not the case.

The issue is reproducible with:
echo -e "\x00\x00\x00\x02\x00" |socat stdin tcp:localhost:2775
---
 openbsc/src/libmsc/smpp_smsc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/openbsc/src/libmsc/smpp_smsc.c b/openbsc/src/libmsc/smpp_smsc.c
index 1e9829b..605bdd5 100644
--- a/openbsc/src/libmsc/smpp_smsc.c
+++ b/openbsc/src/libmsc/smpp_smsc.c
@@ -803,6 +803,12 @@ static int esme_link_read_cb(struct osmo_fd *ofd)
 
 		if (esme->read_idx >= sizeof(uint32_t)) {
 			esme->read_len = ntohl(len);
+			if (esme->read_len < 8) {
+				LOGP(DSMPP, LOGL_ERROR, "[%s] read length too small %u\n",
+						esme->system_id, esme->read_len);
+				goto dead_socket;
+			}
+
 			msg = msgb_alloc(esme->read_len, "SMPP Rx");
 			if (!msg)
 				return -ENOMEM;
-- 
1.8.4.2