On Mon, Jun 29, 2020 at 5:15 PM Eric Dumazet <eric.duma...@gmail.com> wrote:
>
>
>
> On 6/29/20 9:57 AM, Willem de Bruijn wrote:
> > From: Willem de Bruijn <will...@google.com>
> >
> > ICMP messages may include an extension structure after the original
> > datagram. RFC 4884 standardized this behavior.
> >
> > It introduces an explicit original datagram length field in the ICMP
> > header to delineate the original datagram from the extension struct.
> >
> > Return this field when reading an ICMP error from the error queue.
>
> RFC mentions a 'length' field of 8 bits, your patch chose to export the whole
> second word of icmp header.
>
> Why is this field mapped to a prior one (icmp_hdr(skb)->un.gateway) ?
>
> Should we add an element in the union to make this a little bit more
> explicit/readable ?
>
> diff --git a/include/uapi/linux/icmp.h b/include/uapi/linux/icmp.h
> index
> 5589eeb791ca580bb182e1dc38c05eab1c75adb9..427ed5a6765316a4c1e2fa06f3b6618447c01564
> 100644
> --- a/include/uapi/linux/icmp.h
> +++ b/include/uapi/linux/icmp.h
> @@ -76,6 +76,7 @@ struct icmphdr {
> __be16 sequence;
> } echo;
> __be32 gateway;
> + __be32 second_word; /* RFC 4884 4.[123] :
> <unused:8>,<length:8>,<mtu:16> */
> struct {
> __be16 __unused;
> __be16 mtu;
Okay. How about a variant of the existing struct frag?
@@ -80,6 +80,11 @@ struct icmphdr {
__be16 __unused;
__be16 mtu;
} frag;
+ struct {
+ __u8 __unused;
+ __u8 length;
+ __be16 mtu;
+ } rfc_4884;
__u8 reserved[4];
} un;
};
>
>
> >
> > ICMPv6 by default already returns the entire 32-bit part of the header
> > that includes this field by default. For consistency, do the exact
> > same for ICMP. So far it only returns mtu on ICMP_FRAG_NEEDED and gw
> > on ICMP_PARAMETERPROB.
> >
> > For backwards compatibility, make this optional, set by setsockopt
> > SOL_IP/IP_RECVERR_RFC4884. For API documentation and feature test, see
> > https://github.com/wdebruij/kerneltools/blob/master/tests/recv_icmp.c
> >
> > Alternative implementation to reading from the skb in ip_icmp_error
> > is to pass the field from icmp_unreach, again analogous to ICMPv6. But
> > this would require changes to every $proto_err() callback, which for
> > ICMP_FRAG_NEEDED pass the u32 info arg to a pmtu update function.
> >
> > Signed-off-by: Willem de Bruijn <will...@google.com>
> > ---
> > include/net/inet_sock.h | 1 +
> > include/uapi/linux/in.h | 1 +
> > net/ipv4/ip_sockglue.c | 12 ++++++++++++
> > 3 files changed, 14 insertions(+)
> >
> > diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
> > index a7ce00af6c44..a3702d1d4875 100644
> > --- a/include/net/inet_sock.h
> > +++ b/include/net/inet_sock.h
> > @@ -225,6 +225,7 @@ struct inet_sock {
> > mc_all:1,
> > nodefrag:1;
> > __u8 bind_address_no_port:1,
> > + recverr_rfc4884:1,
> > defer_connect:1; /* Indicates that
> > fastopen_connect is set
> > * and cookie exists so we
> > defer connect
> > * until first data frame is
> > written
> > diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
> > index 8533bf07450f..3d0d8231dc19 100644
> > --- a/include/uapi/linux/in.h
> > +++ b/include/uapi/linux/in.h
> > @@ -123,6 +123,7 @@ struct in_addr {
> > #define IP_CHECKSUM 23
> > #define IP_BIND_ADDRESS_NO_PORT 24
> > #define IP_RECVFRAGSIZE 25
> > +#define IP_RECVERR_RFC4884 26
> >
> > /* IP_MTU_DISCOVER values */
> > #define IP_PMTUDISC_DONT 0 /* Never send DF frames */
> > diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
> > index 84ec3703c909..525140e3947c 100644
> > --- a/net/ipv4/ip_sockglue.c
> > +++ b/net/ipv4/ip_sockglue.c
> > @@ -398,6 +398,9 @@ void ip_icmp_error(struct sock *sk, struct sk_buff
> > *skb, int err,
> > if (!skb)
> > return;
> >
> > + if (inet_sk(sk)->recverr_rfc4884)
> > + info = ntohl(icmp_hdr(skb)->un.gateway);
>
> ntohl(icmp_hdr(skb)->un.second_word);
>
> > +
> > serr = SKB_EXT_ERR(skb);
> > serr->ee.ee_errno = err;
> > serr->ee.ee_origin = SO_EE_ORIGIN_ICMP;
> > @@ -755,6 +758,7 @@ static int do_ip_setsockopt(struct sock *sk, int level,
> > case IP_RECVORIGDSTADDR:
> > case IP_CHECKSUM:
> > case IP_RECVFRAGSIZE:
> > + case IP_RECVERR_RFC4884:
> > if (optlen >= sizeof(int)) {
> > if (get_user(val, (int __user *) optval))
> > return -EFAULT;
> > @@ -914,6 +918,11 @@ static int do_ip_setsockopt(struct sock *sk, int level,
> > if (!val)
> > skb_queue_purge(&sk->sk_error_queue);
> > break;
> > + case IP_RECVERR_RFC4884:
> > + if (val != 0 && val != 1)
> > + goto e_inval;
> > + inet->recverr_rfc4884 = val;
> > + break;
> > case IP_MULTICAST_TTL:
> > if (sk->sk_type == SOCK_STREAM)
> > goto e_inval;
> > @@ -1588,6 +1597,9 @@ static int do_ip_getsockopt(struct sock *sk, int
> > level, int optname,
> > case IP_RECVERR:
> > val = inet->recverr;
> > break;
> > + case IP_RECVERR_RFC4884:
> > + val = inet->recverr_rfc4884;
> > + break;
> > case IP_MULTICAST_TTL:
> > val = inet->mc_ttl;
> > break;
> >
