checked in.
tx for your submission.
/hannes
Gerrit Renker wrote:
> This introduces support for variable-length checksum in
> DCCP, as it is specified in section 9 of RFC 4340.
>
> Previously tcpdump was only able to validate full-coverage
> checksums, this patch verifies checksums in accordance with
> the CsCov header field (sec. 5.3).
>
> The patch has been tested and verified on DCCPv4 and DCCPv6
> connections, checksums were manually validated, and traces
> can be supplied.
>
>
>
> In addition, the patch also
> * removes reduplicated code in dccp6_cksum (which
> just repeated the code of in_cksum)
> * fixes a bug in dccp.h -- the fields of CCVAL and
> CSCOV were swapped (cf. section 5.1 of RFC 4340)
> * fixes a typo in the display of incorrect checksums
> (these were printed as `cksum xDEAD (incorrect (-> xBEEF)',
> it now will print `cksum xDEAD (incorrect -> xBEEF)'
>
> I would like to see this merged as a Linux kernel patch already
> exists for DCCP partial checksum coverage support.
>
> Regards
> Gerrit Renker
>
>
> dccp.h | 4 ++--
> print-dccp.c | 34 ++++++++++++++++------------------
> 2 files changed, 18 insertions(+), 20 deletions(-)
>
>
> ------------------------------------------------------------------------
>
> diff --git a/dccp.h b/dccp.h
> index 1afa8c0..8585060 100644
> --- a/dccp.h
> +++ b/dccp.h
> @@ -36,8 +36,8 @@ struct dccp_hdr {
> } dccph_xtrs;
> };
>
> -#define DCCPH_CCVAL(dh) (((dh)->dccph_ccval_cscov) & 0x0F)
> -#define DCCPH_CSCOV(dh) (((dh)->dccph_ccval_cscov >> 4) & 0x0F)
> +#define DCCPH_CCVAL(dh) (((dh)->dccph_ccval_cscov >> 4) & 0xF)
> +#define DCCPH_CSCOV(dh) (((dh)->dccph_ccval_cscov) & 0xF)
>
> #define DCCPH_X(dh) ((dh)->dccph_xtrs.dccph_xtr & 1)
> #define DCCPH_TYPE(dh) (((dh)->dccph_xtrs.dccph_xtr >> 1) & 0xF)
> diff --git a/print-dccp.c b/print-dccp.c
> index e6bfca6..d19c500 100644
> --- a/print-dccp.c
> +++ b/print-dccp.c
> @@ -60,9 +60,20 @@ static const char *dccp_feature_nums[] =
> "check data checksum",
> };
>
> +static inline int dccp_csum_coverage(const struct dccp_hdr* dh, u_int len)
> +{
> + int cov;
> +
> + if (DCCPH_CSCOV(dh) == 0)
> + return len;
> + cov = (dh->dccph_doff + DCCPH_CSCOV(dh) - 1) * sizeof(u_int32_t);
> + return (cov > len)? len : cov;
> +}
> +
> static int dccp_cksum(const struct ip *ip,
> const struct dccp_hdr *dh, u_int len)
> {
> + int cov = dccp_csum_coverage(dh, len);
> union phu {
> struct phdr {
> u_int32_t src;
> @@ -86,15 +97,15 @@ static int dccp_cksum(const struct ip *i
> phu.ph.dst = ip_finddst(ip);
>
> sp = &phu.pa[0];
> - return in_cksum((u_short *)dh, len,
> sp[0]+sp[1]+sp[2]+sp[3]+sp[4]+sp[5]);
> + return in_cksum((u_short *)dh, cov,
> sp[0]+sp[1]+sp[2]+sp[3]+sp[4]+sp[5]);
> }
>
> #ifdef INET6
> static int dccp6_cksum(const struct ip6_hdr *ip6, const struct dccp_hdr *dh,
> u_int len)
> {
> size_t i;
> - const u_int16_t *sp;
> - u_int32_t sum;
> + u_int32_t sum = 0;
> + int cov = dccp_csum_coverage(dh, len);
> union {
> struct {
> struct in6_addr ph_src;
> @@ -113,23 +124,10 @@ static int dccp6_cksum(const struct ip6_
> phu.ph.ph_len = htonl(len);
> phu.ph.ph_nxt = IPPROTO_DCCP;
>
> - sum = 0;
> for (i = 0; i < sizeof(phu.pa) / sizeof(phu.pa[0]); i++)
> sum += phu.pa[i];
>
> - sp = (const u_int16_t *)dh;
> -
> - for (i = 0; i < (len & ~1); i += 2)
> - sum += *sp++;
> -
> - if (len & 1)
> - sum += htons((*(const u_int8_t *)sp) << 8);
> -
> - while (sum > 0xffff)
> - sum = (sum & 0xffff) + (sum >> 16);
> - sum = ~sum & 0xffff;
> -
> - return (sum);
> + return in_cksum((u_short *)dh, cov, sum);
> }
> #endif
>
> @@ -288,7 +286,7 @@ #ifdef INET6
> dccp_sum = EXTRACT_16BITS(&dh->dccph_checksum);
> printf("cksum 0x%04x", dccp_sum);
> if (sum != 0) {
> - (void)printf(" (incorrect (-> 0x%04x),
> ",in_cksum_shouldbe(dccp_sum, sum));
> + (void)printf(" (incorrect -> 0x%04x),
> ",in_cksum_shouldbe(dccp_sum, sum));
> } else
> (void)printf(" (correct), ");
> }
>
>
> ------------------------------------------------------------------------
>
> -
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