smpp_smsc: Check that the size is large enough to hold actual data

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

0 files changed, 0 insertions, 0 deletions