Date: Wed, 12 Jan 2022 08:35:50 -0900 From: Rob Wing <rew@freebsd.org> To: Mike Karels <mike@karels.net> Cc: src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: eb18708ec8c7 - main - syncache: accept packet with no SA when TCP_MD5SIG is set Message-ID: <CAF3%2Bn_eOVx=WwVqO4rHja_3r3sqmj94theYRgqmQaMxU9X5=JQ@mail.gmail.com> In-Reply-To: <1C53233E-B706-4AE8-9928-5AEC09DBD25A@karels.net> References: <202201090145.2091j96M028719@gitrepo.freebsd.org> <1C53233E-B706-4AE8-9928-5AEC09DBD25A@karels.net>
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--0000000000002017c505d566002e Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, Jan 12, 2022 at 6:58 AM Mike Karels <mike@karels.net> wrote: > Sorry for the delayed response; I=E2=80=99ve been out. > No worries. This change seems wrong to me. The TCP_MD5SIG option clearly required MD5 > signatures on all connections in the past, for many years, You're right, since 2017. Before that, TCP_MD5SIG did not require MD5 signature when establishing a connection either. > That meant that connections were limited to peers in the Security > Association Database. A program like a routing daemon could then be sure that it was talking to a > known peer using > signed packets This is still the case, if you've configured a peer to use MD5, it will use MD5. > Redefining the option at this late date seems unsafe and unwise. The option hasn't been redefined. > If there is a use case for a socket that requires MD5SIG for known > peers and not for others, it seems to me that it would be better to add a > new option with those semantics. > The use case is a bgp daemon socket that wants to handle/establish connections with MD5 and non-MD5 peers. For peers configured with MD5, the established connection will be protected by MD5 signatures (i.e., the TCP_MD5SIG option will be set). If a peer is not configured for MD5, then the established connection will not be protected with MD5 signatures (i.e., TCP_MD5SIG will not be set). For what it's worth, this behavior is consistent with OpenBSD. -Rob > > Mike > > On 8 Jan 2022, at 19:45, Robert Wing wrote: > > > The branch main has been updated by rew: > > > > URL: > https://cgit.FreeBSD.org/src/commit/?id=3Deb18708ec8c7e1de6a05aba41971659= 549991b10 > > > > commit eb18708ec8c7e1de6a05aba41971659549991b10 > > Author: Robert Wing <rew@FreeBSD.org> > > AuthorDate: 2022-01-09 01:07:50 +0000 > > Commit: Robert Wing <rew@FreeBSD.org> > > CommitDate: 2022-01-09 01:32:14 +0000 > > > > syncache: accept packet with no SA when TCP_MD5SIG is set > > > > When TCP_MD5SIG is set on a socket, all packets are dropped that > don't > > contain an MD5 signature. Relax this behavior to accept a non-signe= d > > packet when a security association doesn't exist with the peer. > > > > This is useful when a listen socket set with TCP_MD5SIG wants to > handle > > connections protected with and without MD5 signatures. > > > > Reviewed by: bz (previous version) > > Sponsored by: nepustil.net > > Sponsored by: Klara Inc. > > Differential Revision: https://reviews.freebsd.org/D33227 > > --- > > share/man/man4/tcp.4 | 6 +++++- > > sys/netinet/tcp_syncache.c | 30 ++++++++++++++++++------------ > > sys/netipsec/xform_tcp.c | 5 +++++ > > 3 files changed, 28 insertions(+), 13 deletions(-) > > > > diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4 > > index 17138fa224ba..d103293132ba 100644 > > --- a/share/man/man4/tcp.4 > > +++ b/share/man/man4/tcp.4 > > @@ -34,7 +34,7 @@ > > .\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93 > > .\" $FreeBSD$ > > .\" > > -.Dd June 27, 2021 > > +.Dd January 8, 2022 > > .Dt TCP 4 > > .Os > > .Sh NAME > > @@ -339,6 +339,10 @@ This entry can only be specified on a per-host > basis at this time. > > .Pp > > If an SADB entry cannot be found for the destination, > > the system does not send any outgoing segments and drops any inbound > segments. > > +However, during connection negotiation, a non-signed segment will be > accepted if > > +an SADB entry does not exist between hosts. > > +When a non-signed segment is accepted, the established connection is n= ot > > +protected with MD5 digests. > > .It Dv TCP_STATS > > Manage collection of connection level statistics using the > > .Xr stats 3 > > diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c > > index 7dd8443cad65..32ca3bc2209b 100644 > > --- a/sys/netinet/tcp_syncache.c > > +++ b/sys/netinet/tcp_syncache.c > > @@ -1514,19 +1514,25 @@ syncache_add(struct in_conninfo *inc, struct > tcpopt *to, struct tcphdr *th, > > > > #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) > > /* > > - * If listening socket requested TCP digests, check that received > > - * SYN has signature and it is correct. If signature doesn't matc= h > > - * or TCP_SIGNATURE support isn't enabled, drop the packet. > > + * When the socket is TCP-MD5 enabled check that, > > + * - a signed packet is valid > > + * - a non-signed packet does not have a security association > > + * > > + * If a signed packet fails validation or a non-signed packet ha= s > a > > + * security association, the packet will be dropped. > > */ > > if (ltflags & TF_SIGNATURE) { > > - if ((to->to_flags & TOF_SIGNATURE) =3D=3D 0) { > > - TCPSTAT_INC(tcps_sig_err_nosigopt); > > - goto done; > > + if (to->to_flags & TOF_SIGNATURE) { > > + if (!TCPMD5_ENABLED() || > > + TCPMD5_INPUT(m, th, to->to_signature) !=3D 0) > > + goto done; > > + } else { > > + if (TCPMD5_ENABLED() && > > + TCPMD5_INPUT(m, NULL, NULL) !=3D ENOENT) > > + goto done; > > } > > - if (!TCPMD5_ENABLED() || > > - TCPMD5_INPUT(m, th, to->to_signature) !=3D 0) > > - goto done; > > - } > > + } else if (to->to_flags & TOF_SIGNATURE) > > + goto done; > > #endif /* TCP_SIGNATURE */ > > /* > > * See if we already have an entry for this connection. > > @@ -1724,11 +1730,11 @@ skip_alloc: > > } > > #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE) > > /* > > - * If listening socket requested TCP digests, flag this in the > > + * If incoming packet has an MD5 signature, flag this in the > > * syncache so that syncache_respond() will do the right thing > > * with the SYN+ACK. > > */ > > - if (ltflags & TF_SIGNATURE) > > + if (to->to_flags & TOF_SIGNATURE) > > sc->sc_flags |=3D SCF_SIGNATURE; > > #endif /* TCP_SIGNATURE */ > > if (to->to_flags & TOF_SACKPERM) > > diff --git a/sys/netipsec/xform_tcp.c b/sys/netipsec/xform_tcp.c > > index b53544cd00fb..ce2552f0a205 100644 > > --- a/sys/netipsec/xform_tcp.c > > +++ b/sys/netipsec/xform_tcp.c > > @@ -269,6 +269,11 @@ tcp_ipsec_input(struct mbuf *m, struct tcphdr *th, > u_char *buf) > > KMOD_TCPSTAT_INC(tcps_sig_err_buildsig); > > return (ENOENT); > > } > > + if (buf =3D=3D NULL) { > > + key_freesav(&sav); > > + KMOD_TCPSTAT_INC(tcps_sig_err_nosigopt); > > + return (EACCES); > > + } > > /* > > * tcp_input() operates with TCP header fields in host > > * byte order. We expect them in network byte order. > --0000000000002017c505d566002e Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote">= <div dir=3D"ltr" class=3D"gmail_attr">On Wed, Jan 12, 2022 at 6:58 AM Mike = Karels <<a href=3D"mailto:mike@karels.net" target=3D"_blank">mike@karels= .net</a>> wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"mar= gin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1= ex">Sorry for the delayed response; I=E2=80=99ve been out.<br></blockquote>= <div><br></div><div>No worries.</div><div> <br></div><blockquote class=3D"g= mail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204= ,204,204);padding-left:1ex"> This change seems wrong to me.=C2=A0 The TCP_MD5SIG option clearly required= MD5<br> signatures on all connections in the past, for many years, </blockquote><di= v><br></div><div>You're right, since 2017. Before that, TCP_MD5SIG did = not require MD5 signature when establishing a connection either.<br></div><= div>=C2=A0<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0= px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> That meant that connections were limited to peers in the Security Associati= on Database.</blockquote><blockquote class=3D"gmail_quote" style=3D"margin:= 0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">= A program like a routing daemon could then be sure that it was talking to a= known peer using<br> signed packets </blockquote><div><br></div><div>This is still the case, if = you've configured a peer to use MD5, it will use MD5.<br></div><div>=C2= =A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8e= x;border-left:1px solid rgb(204,204,204);padding-left:1ex">Redefining the o= ption at this late date seems unsafe and unwise.</blockquote><div><br></div= ><div>The option hasn't been redefined.<br></div><div>=C2=A0</div><bloc= kquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:= 1px solid rgb(204,204,204);padding-left:1ex">If there is a use case for a s= ocket that requires MD5SIG for known<br> peers and not for others, it seems to me that it would be better to add a<b= r> new option with those semantics.<br></blockquote><div><br></div><div>The us= e case is a bgp daemon socket that wants to handle/establish connections wi= th MD5 and non-MD5 peers.<br></div><div><br></div><div>For peers configured= with MD5, the established connection will be protected by MD5 signatures (= i.e., the TCP_MD5SIG option will be set). If a peer is not configured for M= D5, then the established connection will not be protected with MD5 signatur= es (i.e., TCP_MD5SIG will not be set).<br></div><div><br></div><div>For wha= t it's worth, this behavior is consistent with OpenBSD.<br></div><div><= br></div><div>-Rob<br></div><div>=C2=A0</div><blockquote class=3D"gmail_quo= te" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204= );padding-left:1ex"> <br> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 Mike<br> <br> On 8 Jan 2022, at 19:45, Robert Wing wrote:<br> <br> > The branch main has been updated by rew:<br> ><br> > URL: <a href=3D"https://cgit.FreeBSD.org/src/commit/?id=3Deb18708ec8c7= e1de6a05aba41971659549991b10" rel=3D"noreferrer" target=3D"_blank">https://= cgit.FreeBSD.org/src/commit/?id=3Deb18708ec8c7e1de6a05aba41971659549991b10<= /a><br> ><br> > commit eb18708ec8c7e1de6a05aba41971659549991b10<br> > Author:=C2=A0 =C2=A0 =C2=A0Robert Wing <rew@FreeBSD.org><br> > AuthorDate: 2022-01-09 01:07:50 +0000<br> > Commit:=C2=A0 =C2=A0 =C2=A0Robert Wing <rew@FreeBSD.org><br> > CommitDate: 2022-01-09 01:32:14 +0000<br> ><br> >=C2=A0 =C2=A0 =C2=A0syncache: accept packet with no SA when TCP_MD5SIG = is set<br> ><br> >=C2=A0 =C2=A0 =C2=A0When TCP_MD5SIG is set on a socket, all packets are= dropped that don't<br> >=C2=A0 =C2=A0 =C2=A0contain an MD5 signature. Relax this behavior to ac= cept a non-signed<br> >=C2=A0 =C2=A0 =C2=A0packet when a security association doesn't exis= t with the peer.<br> ><br> >=C2=A0 =C2=A0 =C2=A0This is useful when a listen socket set with TCP_MD= 5SIG wants to handle<br> >=C2=A0 =C2=A0 =C2=A0connections protected with and without MD5 signatur= es.<br> ><br> >=C2=A0 =C2=A0 =C2=A0Reviewed by:=C2=A0 =C2=A0 bz (previous version)<br> >=C2=A0 =C2=A0 =C2=A0Sponsored by:=C2=A0 =C2=A0<a href=3D"http://nepusti= l.net" rel=3D"noreferrer" target=3D"_blank">nepustil.net</a><br> >=C2=A0 =C2=A0 =C2=A0Sponsored by:=C2=A0 =C2=A0Klara Inc.<br> >=C2=A0 =C2=A0 =C2=A0Differential Revision:=C2=A0 <a href=3D"https://rev= iews.freebsd.org/D33227" rel=3D"noreferrer" target=3D"_blank">https://revie= ws.freebsd.org/D33227</a><br> > ---<br> >=C2=A0 share/man/man4/tcp.4=C2=A0 =C2=A0 =C2=A0 =C2=A0|=C2=A0 6 +++++-<= br> >=C2=A0 sys/netinet/tcp_syncache.c | 30 ++++++++++++++++++------------<b= r> >=C2=A0 sys/netipsec/xform_tcp.c=C2=A0 =C2=A0|=C2=A0 5 +++++<br> >=C2=A0 3 files changed, 28 insertions(+), 13 deletions(-)<br> ><br> > diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4<br> > index 17138fa224ba..d103293132ba 100644<br> > --- a/share/man/man4/tcp.4<br> > +++ b/share/man/man4/tcp.4<br> > @@ -34,7 +34,7 @@<br> >=C2=A0 .\"=C2=A0 =C2=A0 =C2=A0From: @(#)tcp.4=C2=A0 =C2=A0 =C2=A0 = 8.1 (Berkeley) 6/5/93<br> >=C2=A0 .\" $FreeBSD$<br> >=C2=A0 .\"<br> > -.Dd June 27, 2021<br> > +.Dd January 8, 2022<br> >=C2=A0 .Dt TCP 4<br> >=C2=A0 .Os<br> >=C2=A0 .Sh NAME<br> > @@ -339,6 +339,10 @@ This entry can only be specified on a per-host ba= sis at this time.<br> >=C2=A0 .Pp<br> >=C2=A0 If an SADB entry cannot be found for the destination,<br> >=C2=A0 the system does not send any outgoing segments and drops any inb= ound segments.<br> > +However, during connection negotiation, a non-signed segment will be = accepted if<br> > +an SADB entry does not exist between hosts.<br> > +When a non-signed segment is accepted, the established connection is = not<br> > +protected with MD5 digests.<br> >=C2=A0 .It Dv TCP_STATS<br> >=C2=A0 Manage collection of connection level statistics using the<br> >=C2=A0 .Xr stats 3<br> > diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c<b= r> > index 7dd8443cad65..32ca3bc2209b 100644<br> > --- a/sys/netinet/tcp_syncache.c<br> > +++ b/sys/netinet/tcp_syncache.c<br> > @@ -1514,19 +1514,25 @@ syncache_add(struct in_conninfo *inc, struct t= cpopt *to, struct tcphdr *th,<br> ><br> >=C2=A0 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0/*<br> > -=C2=A0 =C2=A0 =C2=A0 * If listening socket requested TCP digests, che= ck that received<br> > -=C2=A0 =C2=A0 =C2=A0 * SYN has signature and it is correct. If signat= ure doesn't match<br> > -=C2=A0 =C2=A0 =C2=A0 * or TCP_SIGNATURE support isn't enabled, dr= op the packet.<br> > +=C2=A0 =C2=A0 =C2=A0 * When the socket is TCP-MD5 enabled check that,= <br> > +=C2=A0 =C2=A0 =C2=A0 *=C2=A0 - a signed packet is valid<br> > +=C2=A0 =C2=A0 =C2=A0 *=C2=A0 - a non-signed packet does not have a se= curity association<br> > +=C2=A0 =C2=A0 =C2=A0 *<br> > +=C2=A0 =C2=A0 =C2=A0 *=C2=A0 If a signed packet fails validation or a= non-signed packet has a<br> > +=C2=A0 =C2=A0 =C2=A0 *=C2=A0 security association, the packet will be= dropped.<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 */<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0if (ltflags & TF_SIGNATURE) {<br> > -=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0if ((to->to_flags = & TOF_SIGNATURE) =3D=3D 0) {<br> > -=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0TCPSTAT_INC(tcps_sig_err_nosigopt);<br> > -=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0goto done;<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0if (to->to_flags &= amp; TOF_SIGNATURE) {<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0if (!TCPMD5_ENABLED() ||<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 =C2=A0TCPMD5_INPUT(m, th, to->to_signature) !=3D 0)<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0goto done;<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0} else {<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0if (TCPMD5_ENABLED() &&<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 =C2=A0TCPMD5_INPUT(m, NULL, NULL) !=3D ENOENT)<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0goto done;<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0}<br> > -=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0if (!TCPMD5_ENABLED()= ||<br> > -=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0TCPMD5_= INPUT(m, th, to->to_signature) !=3D 0)<br> > -=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0goto done;<br> > -=C2=A0 =C2=A0 =C2=A0}<br> > +=C2=A0 =C2=A0 =C2=A0} else if (to->to_flags & TOF_SIGNATURE)<b= r> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0goto done;<br> >=C2=A0 #endif=C2=A0 =C2=A0 =C2=A0 =C2=A0/* TCP_SIGNATURE */<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0/*<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 * See if we already have an entry for this = connection.<br> > @@ -1724,11 +1730,11 @@ skip_alloc:<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0}<br> >=C2=A0 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0/*<br> > -=C2=A0 =C2=A0 =C2=A0 * If listening socket requested TCP digests, fla= g this in the<br> > +=C2=A0 =C2=A0 =C2=A0 * If incoming packet has an MD5 signature, flag = this in the<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 * syncache so that syncache_respond() will = do the right thing<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 * with the SYN+ACK.<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 */<br> > -=C2=A0 =C2=A0 =C2=A0if (ltflags & TF_SIGNATURE)<br> > +=C2=A0 =C2=A0 =C2=A0if (to->to_flags & TOF_SIGNATURE)<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0sc->sc_flags = |=3D SCF_SIGNATURE;<br> >=C2=A0 #endif=C2=A0 =C2=A0 =C2=A0 =C2=A0/* TCP_SIGNATURE */<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0if (to->to_flags & TOF_SACKPERM)<br> > diff --git a/sys/netipsec/xform_tcp.c b/sys/netipsec/xform_tcp.c<br> > index b53544cd00fb..ce2552f0a205 100644<br> > --- a/sys/netipsec/xform_tcp.c<br> > +++ b/sys/netipsec/xform_tcp.c<br> > @@ -269,6 +269,11 @@ tcp_ipsec_input(struct mbuf *m, struct tcphdr *th= , u_char *buf)<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0KMOD_TCPSTAT_INC= (tcps_sig_err_buildsig);<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0return (ENOENT);= <br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0}<br> > +=C2=A0 =C2=A0 =C2=A0if (buf =3D=3D NULL) {<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0key_freesav(&sav)= ;<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0KMOD_TCPSTAT_INC(tcps= _sig_err_nosigopt);<br> > +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0return (EACCES);<br> > +=C2=A0 =C2=A0 =C2=A0}<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0/*<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 * tcp_input() operates with TCP header fiel= ds in host<br> >=C2=A0 =C2=A0 =C2=A0 =C2=A0 * byte order. We expect them in network byt= e order.<br> </blockquote></div></div> --0000000000002017c505d566002e--
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