igmp_input() validated the IGMP checksum with:
if (net_chksum((FAR uint16_t *)igmp, IGMP_HDRLEN) != 0)
but net_chksum() returns the raw one's complement sum of the 16-bit
words (it does NOT take the one's complement of that sum). For a valid
IGMP packet whose checksum field holds ~S (as written by igmp_send()),
the sum of all 16-bit words is S + ~S = 0xffff, never 0.
So the existing check `!= 0` was always true for any well-formed IGMP
message, sending every valid packet down the "Checksum error" path to
be silently dropped and breaking IGMP membership query/report processing.
Compare against 0xffff instead, matching the convention used by the
other transport input handlers:
- ipv4_input.c: (ipv4_chksum(IPv4BUF) != 0xffff)
- tcp_input.c: (tcp_chksum(dev) != 0xffff)
This is also consistent with the sender side in igmp_send.c, which
stores `igmp->chksum = ~igmp_chksum(...)`.
Signed-off-by: zhekunren <zhekunren@qq.com>
Assisted-by: GLM-5.2 <noreply@z.ai>
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