Re: [PATCH] checksum: Fix calculation for ICMP checksum on IPv4

Hi, thanks for the quick patch. I can confirm that it works but there is still an issue. The first ICMP package is always dropped: $ podman run --net=pasta alpine ping -c 2 192.168.188.1 PING 192.168.188.1 (192.168.188.1): 56 data bytes 64 bytes from 192.168.188.1: seq=1 ttl=42 time=0.550 ms --- 192.168.188.1 ping statistics --- 2 packets transmitted, 1 packets received, 50% packet loss round-trip min/avg/max = 0.550/0.550/0.550 ms This is a problem in pasta (it works from my host and with slirp4nents), I also see the reply on the host with tcpdump: listening on enp9s0u2u1u2, link-type EN10MB (Ethernet), snapshot length 262144 bytes 14:41:09.457147 IP 192.168.188.22 > 192.168.188.1: ICMP echo request, id 31, seq 0, length 64 14:41:09.457481 IP 192.168.188.1 > 192.168.188.22: ICMP echo reply, id 31, seq 0, length 64 14:41:10.456972 IP 192.168.188.22 > 192.168.188.1: ICMP echo request, id 31, seq 1, length 64 14:41:10.457339 IP 192.168.188.1 > 192.168.188.22: ICMP echo reply, id 31, seq 1, length 64 Paul On Wed, Oct 26, 2022 at 2:16 AM David Gibson wrote:

On Tue, Oct 25, 2022 at 06:07:13PM +0200, Stefano Brivio wrote:

...

We need to zero out the checksum field before calculating the checksum, of course. I have no idea how this passed the "icmp" test set, looking into it.

Reported-by: Paul Holzinger Fixes: 67ab6171729c ("Add csum_icmp4() helper for calculating ICMP checksums") Signed-off-by: Stefano Brivio

Oops, that's embarrassing.

Reviewed-by: David Gibson

...

--- checksum.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/checksum.c b/checksum.c index 09d2c7c..c59869c 100644 --- a/checksum.c +++ b/checksum.c @@ -160,10 +160,13 @@ void csum_udp4(struct udphdr *udp4hr, in_addr_t saddr, in_addr_t daddr, */ void csum_icmp4(struct icmphdr *icmp4hr, const void *payload, size_t len) { - /* Partial checksum for ICMP header alone */ - uint32_t psum = sum_16b(icmp4hr, sizeof(*icmp4hr)); + uint32_t psum;

icmp4hr->checksum = 0; + + /* Partial checksum for ICMP header alone */ + psum = sum_16b(icmp4hr, sizeof(*icmp4hr)); + icmp4hr->checksum = csum_unaligned(payload, len, psum); }

-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson