[lwip-devel] [patch #6760] Ping calculates incorrect checksum

[Robert Sprowson]

Follow-up Comment #4, patch #6760 (project lwip):

[In ping.c in ping_send() et al we have]

size_t ping_size = sizeof(struct icmp_echo_hdr) + PING_DATA_SIZE;
ping_prepare_echo(iecho, ping_size /* 8 + 64 */); 

[In ping.c in ping_prepare_echo we now have]

data_len = len - sizeof(struct icmp_echo_hdr); /* 72 - 8 */
for(i = 0; i < data_len /* 64 */; i++)
{
}
iecho->chksum = inet_chksum(iecho, len); /* 72 */

[In ping.c we used to have just]
for(i = 0; i < PING_DATA_SIZE /* 64 */; i++)
{
}
iecho->chksum = inet_chksum(iecho, len); /* 72 */


So, you're right it will produce a valid packet, but I don't understand what
the extra changes achievey - we now have to calculate data_len at runtime when
in fact it's always just PING_DATA_SIZE.



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