Kirspel, Kevin Kevin-Kirspel at
Sat Jul 1 14:01:35 UTC 2017

I get a crash when running the tcpdump command in LIBBSD.  It is due to the following structure

struct stp_bpdu_ {
    u_int8_t protocol_id[2];
    u_int8_t protocol_version;
    u_int8_t bpdu_type;
    u_int8_t flags;
    u_int8_t root_id[8];
    u_int8_t root_path_cost[4];
   u_int8_t bridge_id[8];
    u_int8_t port_id[2];
    u_int8_t message_age[2];
    u_int8_t max_age[2];
    u_int8_t hello_time[2];
    u_int8_t forward_delay[2];
    u_int8_t v1_length;

In the code, there is an access to the port_id field as follows: EXTRACT_16BITS(&stp_bpdu->port_id).  EXTRACT_16BITS calls ntohs() .  Since the address of "&stp_bpdu->port_id" is at an odd word (16 bit) boundary, an exception is generated.  What is the correct way to fix this?  I was going to update EXTRACT_16BITS to check for an odd boundary and fix it up before calling ntohs().

Kevin Kirspel
Electrical Engineer - Sr. Staff
Idexx Roswell
235 Hembree Park Drive
Roswell GA 30076
Tel: (770)-510-4444 ext. 81642
Direct: (770)-688-1642
Fax: (770)-510-4445

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