Linux؇ernel؋e఍or༂ng – - PDF document

Linux؇ernel؋e఍or༂ng – advanced،opicᜆ(5) ؆؆؆؆؆؆ Soᔏeగ ĭజe؏ࠉ̈l RamȆᴎᜈn ramȉosࠟgmሂl.cพ HaȢЅ, AugЗt ┦☧ w഍.ᰒȢux.org AlਆrȐᰌs reservࠓ. LinuԆ܈rnel؋e఍or༂ng (5)- advanced،opics Nฌࠩ Thȗ ਈctЉࠆȗ ሆᜈ⬄ࠊ tฆtᰈ foਊญȃဆ4 ਈctЉes I gave ȃ ℒifux: Ănux Kenr਋ ਌nഊokgN–x antlጎKNln http://www.haifux.org/lectures/172/ vtxclv http://www.haifuԠoऐ/lectuईᜮ172/netLec.pdf pi sc(5 dਕnux Kenr਋ ltnwlokgN–x an)nn wਅaShgNx anᴇhvḔoਟnᤆcn.ℝlጃtlጎKNl http://www.haifux.org/lectures/180/ vtxclv http://www.haifuԠoऐ/lectuईᜮ180/netLec2.pdf LinuԆ܈rnel؋e఍or༂ng (5)- advanced،opics finsc(5 ጊcnux KenऊN ltnwlokgN–x an)n nnnnn .Hᠣnx noSਃux Kenr਋ ltntਓoKNl httᘩ//഍w.hሂfЅ.ฉg/ਈctЉes/⼱7/ Rtxclv : http://www.haifuԠoऐ/lectureᜮ187/netLec3.pdf ␂n2xN਌ਔvnx nux Ke http://www.ᰒȢux.org/ਈcturࠗ/┦㌮ Rtxclv : http://www.haifuԠoऐ/lectureᜮ206/wirele᜗Lec.pdf Tሴਈ of cǒěᜩ The ĂnЅ Ke system ᔒll. UDP protoᔎl. Control Messageᜠ AppendiԈᜠ Nฌࠩ Aਊ cณࠆexሞpਈs ȃ thȗ lࠕture rࠢer to thࠆrࠕࠃt p0,0f9 versȎ̆of the ĂnЅ ༈rnࠊ. Ē㔈आ2 ᠺAC lስeच Ē㔈आ3 ᠋ࠌഎए lስࠉ: IPV4/IPV6) Lስࠉ ⰆᠪCP,㘷P,S㤪P,...) –lN lt TCP sต༈t UDP ؛ocket -vlNv:5dln In؄serؗpaᔈ,؍e؜aᐈ appliᔒంon,ؗe᜗ionؒndؖresentaంon la㔈r᜘కp⸂p؉efers،oؒll 3ؒsؒpplicaంon؊a㔈r) crࠒtȃg a sตkࠌ TNg@nKv਋nᐩ5dਃ ȗ dö by thࠆ LinuԆKe system ᔒਊ: int socket (int family, int t㔖e, int protocol); From man 2 soᔏet: RETURN VALUE On ᜄcce᜗, a file de᜕ंptoआfoआthe new ᜎc༈t iᜆreturned. Foआopen᠚ ᜵ᜌem call ᠢor file᜚, we alᜎ get a file de᜕riptoआ aᜆthe ईtuः ᐒlue. Eveवthȃg is a fȊࡁ Unix ᘒऒdigḠ Theآirsఆparameఈr,آamily,؂ᜆalsoؗomeంmeᜆreferred،oؒsـdomain”. The ⨙@xtm iᜆPF_INET for IPV4 oआPF_INET6 foआIPV6. The family is PF_PACKET for Pac༈t ᜎc༈tᜣ which opeऒte at the deᐂce driᐈआla㔈r. ᠁a㔈आ2ᨠ pcap libऒव foआLinuԆuᜈᜆPF_PACKET soc༈tᜩ pcap libraव iᜆin uᜈ b㔆ᜃiffeग such as tcpduḖ. Alᜎ hostapd uᜈᜆPF_PACKET soc༈tᜩ (hoᜌapd is a wiईle᜗ acce᜗ point ḒnageḈnt pऎject) Fऎm hoᜌapd: dऔ-䐞onitor_ᜎc༆= ᜎc༈tᠸF_PACKET, SOCK_RAW, hton᜘ETH_P_ALLᨚ; Type: SOCK_STREAM and SOCK_DGRAM aई the moᜌl㔆uᜈd t㔖eᜠ SOCK_STREAM foआTCP, SCTP, BLUETOOTH. SOCK_DGRAM foआUDP. SOCK_RAW for RAW ᜎc༈tᜠ Theई aई caseᜆwhere pऎtocol can be eitheआ SOCK_STREAM ngN SOCK_DGRAM; foआeԒḖle, UniԆ doḒin ᜎc༈t ᠤF_UNIXᨠ Protocol:uᜄall㔆0 ᠆IPPROTO_IP iᜆ0, ᜈe: include/linuԮin.h). FoआSCTP, the protocol iᜆ .HHq4I4/R1IH soᔏfd=ᜎᔏet(A㵂INET, SOCK_STREAM, .HHq4I4/R1ⴡ Foआbluetooth/RFCO㨺: ᜎc༈t(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMMᨼ SCTP: StईaḆControl Tऒn᜞i᜗ion Protocol. For every soᔏet which is created b㔆a uᜈr᜖ace application, there is a ᔎrresponding vgd–lo struct and vgd– ᜌruct in the kernel. This system ᔒll eᐈntually inᐎkeᜆthe Līr̊xN xKe wx oiktg–t oxtЅl–xad v–tg–ĆN–nxtict Ćlp̆tLinЅ tgČ̊xN xkt Kg–napkxsag–p(s–x doet L؊p̆t Linux ఎNČi–a5చtwxwSxlĜtĆlp̆t Linu ఎNČwilxt؎N–ఝmἌ N–kఐČi–xంcఆoxఛg..xĆఁ؊p̆plxLఐ–ఆox఑xءilА–.tĆN̄dtfipt nN–అNĐa5ఛxఃi–ᔖąkఛxءxx–ఆoxwdణiఆoxఃi–Ax– gi–ఐČ؎gL┌ Linu Linu ఋaHNᤁఊxcxlLఆit Ćlp̆ఁīxؓ Lu Lu tNaHNᤁఊxᔅlLఆit Ćlpn،Ă̄ struᔌ ᜎck: (include/net/soᔏ.h) strЕt ᜎᔏ { ... strЕt soc༈t *ssoc༈t; struᔌ ᜎcket (inᔊude/linux/net.h) strЕt ᜎᔏet { soc༈t䈗tate state; sᰎrt tyᘈ; Ѓsig̈ጆlo̐ flags; strЕt fasync䈗trЕt *fas㔃ᕂlist; wait䈫ЈЈ䈜ࠒd䈌 wait; strЕt file *fil࠼ strЕt ᜎᔏ *s༼ conᜌ strЕt ᘉoto䈎ᘗ *op᜼ }; Theؗఒఈؕanشe SS_FREE SS_UNCONNECTED SS_CONNECTING SS_CONNECTED SS_DISCONNECTING Theᜈ ᜌateᜆaई not la㔈आ4 ᜌateᜆ᠊i༈ TCP_ESTABLISHED or TCP_CLOSE). The ᜏ_pऎtocol meḴer of ᜌruct ᜎc༆equalᜆto the third paऒḈteआ(pऎtocolᨆof the Ă̄x Ke ᜵ᜌeḆcall. struct ᘉฌo_ถᜆ(ȃtࠉfacࠆย strЕt sต༈t) x lฮᐎNl᤟/g:v ᠂.ࠠ, TCP sต༈ts) x lฮcaଙ@/g:v ᠂.ࠠ, 㘷P sต༈ts) x lฮᐐdᄋᤏ/g:v ᠂.ࠠ, RAW sต༈ts) .family PF_INET PF_INET PF_INET .owner THIS_MODULE THIS_MODULE THIS_MODULE .releaᜈ inet_release inet_release inet_release .bind inet_bind inet_bind inet_bind .ᔎnneᔌ inet_stream_connect inet_dgram_connect inet_dgram_connect .ᜎcketpair socགno_socketpair socགno_socketpair socགno_socketpair aᔕept inet_accept socགno_aᔕept socགno_aᔕept .getname inet_getname inet_getname inet_getname .poll tᔖ_poll udp_poll datagram_poll .ioctl inet_ioctl inet_ioctl inet_ioctl .listen inet_listen socགno_listen socགno_listen .᜜utdown inet_shutdown inet_shutdown inet_shutdown .ᜈtsoᔏopt socགcommon_setsoᔏopt socགcommon_setsoᔏopt socགcommon_setsoᔏopt .getsockopt socགcommon_getsockopt socགcommon_getsockopt socགcommon_getsockopt .ᜈndmsg tᔖ_sendmsg inet_sendmsg inet_sendmsg .recvmsg socགcommon_recvmᜐ socགcommon_recvmᜐ socགcommon_recvmᜐ .mmap socགno_mmap socགno_mmap socགno_mmap .ᜈndpage tᔖ_sendpage inet_sendpage inet_sendpage .᜖lice_read tᔖ_splice_read Note: The inet_dgraṂopᜆand inet_ᜎc༉aw_opᜆdiffer onl㔆in the .poll ḈḴer: in inet_dgraṂopᜆit iᜆ pk0r0iaa܈ in inet_ᜎc༉aw_opᜣ it iᜆ kN N.਋wr0iaa܈d Diagraḩ strЕt inࠌ_sock stऄᔌ soᔏ ᠗༚ stऄᔌ iᙂoᘌȎns *ถt; _䈄8 tos; _䈄8 ईᔔeउ:⼼ _䈄8 hdं̕਩⼼ ..... inet_ᜏ᠗oc༆*ᜏᨆ=䐆returnᜆthe inet_ᜎc༆which containᜆᜏ ᜌrЕt soc༆ᰒs threࠆ⬄ࠄࠗ: rx , tx a̓ ࠉr. sག㐄ff sག㐄ff sགbuff sགईᔈȔࡂ⬄eue sག㐄ff sག㐄ff sགbuff sགഉȌࡂ⬄ࠄe 7ᤓSn8KlKlnSᤔn5ntgd–n3ᐩx tgdᄂ sག㐄ff sག㐄ff sགbuff sགࠉऎr_⬄ࠄe ☃0̦̦ 0̦̦̦n 0̦̦̦n LuSधpxpxआNဒKet2tvkkg–.t it oxt9pxpx LuSएx9pxᘅKet2tlxwiAထ.tclȍt oxt✖xpx -g ot:,Trq44I@t ogČgČki–xtg–t HitL N.xL2 LЛr0xxuKet rrĄSrp–ag–uKedtK itlxwi␅t oxtĄrSpcctcliwt oxt 9pxpxed Fฉ the ࠉror qЈuࠩ Līr9pxᘅrxllrLuᬇe ሓds tฆȌs tሂਆ ᠂nᔊud࠮net/sตk.h) . Eᐈ̌Вlਵ, Ȍ ሊᜎ ᔒਊs Luᬉ9pxᘅr Ngሇedt Erऎग can be ICMP eउorᜆoआEMSGSIZE eउoग. FoआḎई about eउorᜣᜈe APPENDIX F: UDP erऎग. UDPؒ̓ ⨹P ଎ explȕȌ ᔎ̃ࠕtȎn setЖ ȗ dö wȌh UDP. In TCP there is a preliminar㔆ᔎnneᔌion setup. Pac༈ts că㐈 ਎st ȃ U㜸 (tᰈre ȗ nฆ rࠌrሃsmȗᜂฃ mechâsm ȃ the ༈r̈l). TCP ฃ thࠆฌher ᰒ̓ ȗ rࠊȒbਈ (thࠉࠆis ሆ rࠌrሃsmȗᜂฃ mechâsm). Mทt ย the Ǐer̈t traffȕ ȗ T㤸 (ਂ༈ httᘣ ssh). UDP iᜆfor audio/ᐂdeo (RTP)/streaming. Note: ᜌईaḂng with VLC is b㔆UDP ᠝TP). StreaḂng ᐂa YouTube iᜆtcp ᠜ttp). The udp؜eader Thereؒreؒؔer㔆fewضDP-basedؗervers؊ikeطNS⌆NTP⌆ DHCP⌆TFTPؒnd؞ore. ForطHCP, it؂ᜆquiఈ؃aఄral،oشeضDPؘSinᔈ man㔆ంmes؍iజ DHCP,صouؓon'ఆhaᐈؒؗourceؒddre᜗,؍hiᔜ؂ᜆa؞usఆfor TCP). TCP؂mplemenఒంon iᜆmuch؞oreؕomplex The TCP header؂ᜆmuᔜشigger జanضDP؜eader. The udp header: tg–̒pkxsag–p᠗pk0do stऄᔌ udphdआ{ 䉂㐈⼳ sคrc࠼ 䉂㐈⼳ dࠗt; 䉂㐈⼳ ਈn; 䉂suḯ6 ᔜࠕ༼ UDP pac༈t = UDP heሓer + pay਎ad Aਊ mࠞbers arࠆ2 bytes (16 bȌs) souकࠆᘎऌ dest pฉt ਈn ᔜeᔏsum H5mఐ5c Receiving paᔏets؂nضDP ∉om kernel UDP ༈rnel ᜎc༈tᜆcan get tऒffic either from uᜈगpace or froḆkeःel. UDP – ਒㔈आ4 IPᐬ - ਒㔈आ3 nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn -R7⬃RHᜯ7 nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn -㌡nvgd–lด Kerli̋lrtxlKഅฉ༇gKL–ሓ nଊlĔcteऎ̍ad psr(p5)rShᴞSr(pv –iiu r7qരu LinЉ@cxcxऎ̍rĄ.ሓ Lስࠉ 2 ᠾtheःࠌ) From Kv਋nv:ᤓl , 㔎Іcሃ rࠕࠂve udp traffȕ ĭ threࠆ᜵stࠞ caਊs: lx̤KettKHox–t oxtLīx tgČni––x̆xke lx̤cliwKe lx̤wĠKe All thईe aई handled b㔆 pk0rਅ̤ഁ.Kࠌ in the ༈ःel. /i xt oN tcipl ot0N਋wx xltict oxąt1tഅ oikLtgLtcaN.Ĝt oiHx␅l@t ogČ0NlNഅ x਌gČ/78t̎N–.xktp0i–tਅ pl–dt3ctᤂptNਅt g– xਅĆxktg–tlx pl–xktcaN.Č@t5iptwpĆtpąt iglH tਅ̤ഁ.KࠟtN–kt itਅ ਐx␅t oxtwĠdwL.rcaN.Čഅഛxldt FoआexaḖle, suppoᜈ 㔎u have a client-ᜈऔer udp applicationᜣ and the ᜈnder ᜈndᜆa packetᜆwhich iᜆlongeआ then what the client had allocated foआinput buffer. The ༈rnel than tऄncateᜆthe pac༈t, and send 㐝y/Iq-w1 flag. In order to ईtंeᐈ it, 㔎u ᜜ould use ᜎḈthing li༈: ईcᐞᜐ᠄dpSoc༈t, &ḗg, flag᜚; if ᠞ᜐ.ḗg_flagᜆ& 㨛G_TRUNC) pंntf(刺SG_TRUNC\n刚; Therࠆഒs ሆnࠍ sАဈstiฃ rࠕࠃtly fฉ lxn␍wL.Ke tL5L xwtnNሒtciltlxnxဤg–.twpሆဦህt wxāN.ԁtK㌙tvlᄋሏitbNlANሎitkxt:xሂe 8oxt lx̤഍L.܈ tHgaatlxkp̅t oxti␅਎xNkt̋pąktS5tഖa g0axt ęĆxഌ̋aaČictਅn␍Ġ܈tg–t oxtpĖNat̋ąd Receiving paᔏets؂nضDP ∉om user space UDP ༈rnel ᜎc༈tᜆcan get tऒffic either from uᜈगpace or froḆkeःel. UDP – ਒㔈आ4 IPᐬ - ਒㔈आ3 nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn -R7⬃RHᜯ7 nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn -㌡nvgd–lด r7qരu cteऎԃഢL,ሓ nnnnnnnn ଊdᠪଐἲinvḔชἃdᤌt उLРऎԃwऌଆN,oଢadv␔ ฅଌĔ༎i∔vĄ┦Ąrฅ̅Kwԉ@cxcx Lስࠉ 2 ᠾtheःࠌ) ଊdᠲinvḔጙttnd5tt ଊd᠟ᐒ3inᐞᐓ5tt Reᔈiᐂng packeగب؄dp_rᔔ() pk0ऊnAKe ȗ tᰈ ᰒ̓lࠉ for aਊ U㜸 ᘒckࠌᜆ frพ the IP ਒yer. It ha̓ਈs ሊਆȃcพȃg pሕkࠌs ȃ which tᰈ protocช fȈਓ ȃ thࠆip hࠒdࠉ ȗ I㠸ᴿTO_U㜸 (1〚 ሢtࠉ ip ਒yࠉ fȃȗhࠓ wȌh them. See the udp_protocol definition: (net/ipᐬ/af_inet.c) ᜌruct net_pऎtocol udp_protocol = { .handler = udp_rcv, .erूhandleआ= udp_eउ, ... }; Ĭtᰈ ᜒme way we havࠆ: lNHrln␇e as a handler for raw paᔏetᜠ n0r␵rl̤Ket as a handler for TCP paᔏets. g̍0rl̤Ke as a handler for ICMP paᔏets. Ker̈l ȞᘊࠞࠃtሌȎ̩ the 0lȆirlx‐L ԊKet mࠌhณ rࠐȗters ሆprotตoਆha̓lࠉ. (net/core/ᜎc༠c) pk0rl̤Ketgw0axwx– N gi–2 For broadᔒsts and multicaᜌ – there is a speᔂal treatment: ifؘrt->rt_flagᜆ&ؘRTCF_BROADCAST|RTCF_MULTⴹAST)) reఄrn __udp4_lib_mᔒsూdeliᐈr(neణؗkb,؄h, ᜒddr, daddr, udpఒble); Then perform a lookup in a hashtable of struct soᔏ. Ha᜜ ༈㔆iᜆcईated froḆdeᜌination poऌ in the udp header. If theई iᜆno entव in the ha᜜table, then there iᜆno ᜎck liᜌening on thiᜆUDP deᜌination poऌ 䕄 ᜎ ᜈnd ICMP bac༩ ᠎f n:gNonK Nl5dS5htl icḖ_ᜈnd(ᜏb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH , 0ᨼ udp_rcv() Ĭtᰂs case, ሆᔎrrespo̓i̐ ᬋMP MIB cค̌er ȗ ȃcrࠞěࠓ (UD㡂MI䡂NOPORTᬚ. UDP_INC_STA⨛_BH(net, UDP_MIB_NOPOR⨛, proto == IPPROTO_UDPLI⨾); Yค căseࠆit by: –x ĆN tUL ddddd Udp: ... 35 paᔏets to unknown port reᔈiᐈd. ... udp_rcv()ب conఓ Or, by: cሌ /proc/̈t/ᜃmᘆ| grep U጖: Udp: I̷ሌagrams ଎㠎rts I̾rrฉs OutDሌሐrሞᜆRcv㐄f㸉rฉs SndbТErrors Udp: ⼬ 35 0 30 ☆0 If therࠆȗ a sตk ਂstࠃȃဆฃ the dࠗtȃatȎn pฉt, caਊ ᘏ0r9ᘅpxrlnArLЛKed 4Ax– pNaaᤌ̋aaLtĂ̄r9pxpxrln␉LЛKed Which addᜆthe pac༈t to the v–/Nldlx(l/8KlKl by ĄSr9pxpxr NgaKe udp_rcv()ؓiagram u጖䈉ᔔ᠚ _䈄dpⱂਂb䈉ᔔ Multȕሗt _䈄጖ⱂਂ㑂ḕast䈓ࠊȔer Ûᔒst 䉂udpⱂlȴ_਎ฏup䈗༴ Fȃጆሆsoᔏ in Гᘌሴਈ udp䈫uࠄe䈉ᔔ䈗༴ soᔏ䈫uࠄe䈉ᔔ䈗༴ Dฃ't find ሆsต༆ iᔞᙂsࠃd᠚ ICMP䈷EST_UଝEAC℣ I㤺P䈸ORT䈶NᴾA㤡 pk0ऊxnAwL.Ke2 Cሊਗ tउLuSऊxnAएN N NwKe , fฉ receȔȃg ฃࠆsk_buff. The rrĄSrlxn␉kN N.lNwKe may bloᔏ. Eᐈntually, what rrLЛrlxn␉kN N.lNwKet does iᜆ read one sགbuff from the ĄrlxnxgAxr9pxpx queue. wxwn☙r igiAxnKe pࠉfฉms the ሕtВਆcopy to Зer sᘒcࠆby i̔o༂̐ ni0ᤉ irᘁxlKed Onࠆof thࠆpሉሞetࠉᜆย ᘏ0rlx̤wL.Ke ȗ ሆ pข̌er to struct fL,–to . Lࠌ's tሏe a ਎o༩ MᭇHDR FroḆinclude/linuԮᜎc༈t.h: ᜌऄct ḗghdआ{ ᐎid *ḗg_naḈ; /* Soc༈t naḈ */ int ḗg_naḈlen; /* Length of naḈ */ ᜌऄct ioᐈc *mᜐ_ioᐼ /* Data blocks */ __༈ःel_ᜂ唈_t ḗg_ioᐊen; /* Number of bloc༗ */ ᐎid *ḗg_contऎl; __༈ःel_ᜂ唈_t ḗg_controllen; /* Length of cḗg liᜌ */ unᜂgned ḗg_flag᜼ }; Control؞e᜗ageᜆ(ancillar㔆 me᜗ages) The ḗg_contऎl ḈḴer of mᜐdhr repईᜈnt a contऎl me᜗age. Sometimes 㔎u need to perform some speᔂal things. For eԒmple, getting to know what was the destination addresᜆof a receiᐈd packet. SometiḈᜆtheई iᜆḎre than one addई᜗ on a machine ᠒nd alᜎ 㔎u can haᐈ Ḅltiple addई᜗eᜆon the ᜒme nicᨠ How ᔒn we know the destination address of the ip header in the appliᔒtion? ᜌruct nd@vaScN (/uᜉ/inᔊude/bits/socket.h) represents a control mesᜒge. cḗghdr ḈḴeग can mean diffeईnt things baᜈd on the t㔖e of ᜎcket. There iᜆa set of macऎᜆfor handling cmᜐhdr li༈ CMSG_FIRSTHDR᠚, CMSG_NXTHDR᠚, CMSG_DATA(ᨣ CMSG_LEN᠚ and Ḏre. There are no contऎl me᜗ageᜆfoआTCP ᜎc༈tᜠ ᬎc༈t؎ptions: In order to tell the ᜎc༈t to get the inforḒtion about the pac༈t deᜌination, we ᜜ould call ᜈtᜎc༎pt᠚. ą Ă̄i0 Ke and .x Ă̄i0 ܈ ⠆ᜈt and get optionᜆon a ᜎc༈t. Both Ḉthodᜆreturn 0 on succe᜗ and ⠯ on erऎr. Prototype: int ᜈtᜎc༎pt(int ᜎc༢d, x o tl(lt , int optnaḈ,... There are two leᐈlᜆof ᜎc༈t optionᜩ To manipulate optionᜆat the ᜎc༈tᜆAPI leᐈl: SOL_SOCKET To manipulate optionᜆat a protocol level, that pऎtocol nuḴeआ ᜜ould be uᜈd; foआexaḖle, foआUDP it iᜆ IPPROTO_UDP or SOL_UDP (both aई equal 17ᨆ; sࠈ ȃᔊude/lȃЅ/in.ᰆand ȃᔊГ࠮ਂnuԮsต༈t.h SOłIP is 0. Theई are curईntl㔆19 LinuԆsoc༈t optionᜆand one anotheआon option for BSD compatibility. See AppendiԆB for a full liᜌ of ᜎc༈t optionᜠ Theई iᜆan option called IP_PKTINFO. We will ᜈt the IP_PKTINFO option on a ᜎc༈t in the following eԒḖle. // fऎm /uᜉ/include/bitᜮin.h #define IP_PKTINFO 8 /* bool */ /* Stऄctuई uᜈd foआIP_PKTINFO. */ ᜌruct in_pktinfo int ipi_ifindeԼ /* Inteढace index */ ᜌऄct in_addआipi_spec_dᜌ; /* Routing destination addईss */ ᜌऄct in_addआipi_addr; /* Headeआdeᜌination addre᜗ */ conᜌ int on = 1; ᜎc༢d = ᜎc༈tᠤF_INET, SOCK_DGRAM,0ᨼ if ᠗etᜎc༎pt(ᜎckfd, SOL_IP, IP_PKTINFO , &on, ᜂ唈of᠎n)ᩘ0) peउoघ列etᜎc༎pt刚; ... ... ... Whenؕalling reᔔmsg(),؍e؍illؖarᜈ،he؞sghr؊ike،hiᜩ forؘcmpఉ=CMSG_FⴝSTHDR(&mᜐ);ؕmpఉ奅NULL; ᔞpఉ=CMS䝂NXTHDR(&mᜐ,cmpఉ)) ifؘcmptr->cmsg_leᐈlم=؛OL_IP &&ؕmpఉ->ᔞᜐ_వpeم= IP_PKTINFO ؆؆ ؆؆ pkంnfoمؘᜌrucఆin_pkంnfo*)CMSG_DATA(cmptr); printf("deᜌinaంon=%s匃", ineూnఎp(AF_ⴋET, &pktinfo->ipi_addr, ؆؆؆؆؆؆؆؆؆ ᜌr⌆ᜂ唈of(ᜌr))); Ĭtᰈ kࠉnࠊ, thȗ cሊls ဦःwL.rlx̤Ket ̈t/Ȗᐬ/Ȗ_ᜎckg਄e.c. (ജȕh evěВਊy cሊls ဦrnwL lxn␉0u g–ciKe ). Yค căȃ this way retrȈvࠆother fȈਓs of the Ȗ hࠒdࠉ: For getting the TTL: ᜈtᜎc༎pt᠗oc༢d, SOL_IP, IP_RECVTTL , &on, ᜂzeof᠎nᨚ<0). But: cḗg_t㔖e =䔆IP_TTL. For getting ip_options: ᜈtᜎc༎pt᠚ with IP_OPTIONS. Nฌࠩ yค cãot get/set Ȗ䈎ptȎns ȃ Jሔሆ ሖᘠ ᬈndingؖac༈ts inضDP From Kv਋nv:ᤓl , 㔎Іcሃ sࠃd udp trሢfȕ wȌh threࠆ᜵stࠞ caਊs: Lx–kKetKHox–t oxtLīx tgČni––x̆xked Lx–k iKe Lx–kwĠKe All thईe aई handled b㔆 pk0rą–kഁ.Kࠌ in the ༈ःel. pk0rLx–kwL.܈t iᜆḄch ᜂḖleआthan the tcp paऒllel Ḉthod , ̦rą–kഁ.Kࠓ pk0rLx–k0N.x܈t iᜆcalled when useआ᜖ace callᜆ ᜈndfile(ᨆ(to cop㔆a file into a udp ᜎc༈t). sendfile() ᔒn be used also to ᔎpy data between one file descriptor and another. pk0rLx–k0N.xKetg–AiЅLtpk0rą–kwĠKed p༦ँԑ༦ଠx܈tHဒሌℂ਄tȑሙtပt ฅt–ဃtĖ0☂ਆČ ,nN xlsTଆฅ਌ܮ483DrDr,TtcxଆᘊxtgČĖ☦iਆx༈d Exampleؑ udpؕlient #include #include #include #include int main() int s; struᔌ soᔏaddr_in target; int res; char buf[10]; target.ᜂn_family = AF_INET; target.ᜂn_port=htons(999); inet_aton("192.168.0.121",&target.ᜂn_addr); strᔖy(buf,"mesᜒge 1:"); s = socket(A㵂INET, SOCK_DGRAM, 0); if (s<0) perror("soᔏet"); res = sendto(ᜣ buf, ᜂzeof(buf), 0,(struᔌ sockaddr*)&target, sizeof(struct soᔏaddr_in)); if (res<0) perror("sendto"); elᜈ printf("%d byteᜆwere sent\n",res); Foआcompaंᜎn, there iᜆa tcp client in appendiԆC The soЉce port ย the UDP pሕ༈t herࠆȗ chทࠃ rሃdพਵ ĭtᰈ kࠉ̈ਠ If I ഒ̌ tฆᜈnd frพ ሆspࠕȢȈd pฉt ? You can bind to a ᜖ecific ᜎurce poऌ (888 in thiᜆeԒmpleᨆby adding: ᜎurce.sin_famil㔆 䔆AF_INET; ᜎurce.sin_poऌ = hton᜘888ᨼ ᜎurce.sin_addr.ᝂaddआ 䔆htonlᠭNADDR_ANYᨼ if ᠴind᠗, (ᜌऄct ᜎckaddोᩑᜎuकe, si唈of᠗tऄct ᜎc༒ddूinᨚ 䕅 ⠯) peउoघ刴ind刚; Yค ጙ gon bȃd to privȊࠐࠓ pฉts (ports ਎wer thሃ ⼦┬) kSl nmgKnᤋਃ gonNggonU Tr㔂ng to do this will giᐈ: Permission denied” ( 7H7qb ). You can enable non root binding on priᐂleged port by running as root: (You will need at least a 2.6.24 ༈rnel) ᜈtᔒp 'cap_net_bind_ᜈrviᔈ=+ep' udpclient This ᜈtᜆthe 1sH/w7I/D.w6/R7qP.17 capability. Yค cãot bȃd ŏa pฉt ജȕh is ሊrࠒdy bค̓. Tr㔂ng to do this will giᐈ: Addre᜗ alread㔆in use” ( 7s66q.w-R7 Yค cãot bȃd okxጊngNn@gNln wȌh tᰈ same UDP sต༈t (ࠔĕȢ yค cᰒ̐ࠆtᰈ port). You will get “bind: Inᐒlid argument” error in ᜄᔜ case 37.wPsui If yoІtr㔆 niᄑxn Ke ฃ ău̴oЃጆUDP soc༈t ሃd thĕ ᬐ–kKe yค wȊਆaਗฆဈt thࠆ㸭NVAL ࠉrฉ. The rࠒsŏȗ thሌ cõectȃg to ሃ Ѓbคnd soc༈t ംਊ cሊਆ ထx ऋp iᬐ–kKe tฆ ሄtพatȕaਊ㔆bȃd ሃ Ѓbค̓ sตkࠌ (ฃ a rሃdพ pฉt). Sฆሢter cõect(), thࠆᜎckࠌ is bค̓ed. A̓ thࠆcሊlȃg bȃጘ) ሐሂn wȊl fሂl wȌh EI଻AL (si̕e the sตkࠌ ȗ aਉࠒdy bฃdࠓ). Bȃdȃဆȃ the ༈r̈l fฉ UDP ȗ Ȟplࠞěed ȃ ထx छထ༇etN–༌ထԆrNp țထkKet Kg–t3qPC2tg–x CrSg–kKete Non؊ocalشind What happenᜆif we tव to bind on a non local addre᜗ ? ᠒ non local addई᜗ can be foआexaḖle, an addईss of inteढace which iᜆtempoऒrily down) We get EADDRNOTAVAIL error: bind: Cannot assign requested address.” Howeᐈr, if we set /proᔮs㔗/net/ipᐬ/ip_nonloᔒl_bind to 1, by echo 刯" > /proc/s㔗/net/ipᐬ/ip_nonloᔒl_bind Or adding in /etᔮ᜵sctl.ᔎnf: net.ipᐬ.ip_nonloᔒl_bind=1 The Sg–kKet will sucᔈed, but it may sometimes break applications. What will happen if in the aboᐈ udp client eԒmple, we will tव ᜈtting a bऎadcaᜌ addre᜗ aᜆthe destination (inᜌead of 192.168.0.121ᨣ thuᜩ inet_aton( 別55.255.255.255" ,&target.ᜂn_addच; We will get EACCESS eउoआ(“Peञi᜗ion denied”ᨆfoआ ą–k iKe 3–tilkx਌ oN tMVqtSਂNk̋ĆtHgaatHi਄@tHxtoN␅t itNkk2 g– tcaN.t;tFh gctKą Ă̄i0 tKğt,7Er,7bI48@t,7r6O7vVbv,8@“caN.@t Đ䄅icܕaN.ࠈt䈌me 0xਊil݃ą Ă̄i0 䌈h UDP soc༈t؎pంons Fฉ .HÅ4I4/-㌡CR4u/-6Hn ਈvࠊ, we hሔࠆ two sต༈t ถtȎns: UD㡂CORK sต༈t ถtiฃ. Added in Linux kernel 2.5.44. nt ᜌate䔯; ᜈtᜎc༎pt᠗, IPPROTO_UDP, UDP_CORK, &ᜌate, ᜂ唈of᠗tate)ᨼ foआᡃ䔯;j堯000;j偐) ᜈndto᠗,buf1,...) ᜌate=0; ᜈtᜎc༎pt᠗, IPPROTO_UDP, UDP_CORK, &ᜌate, ᜂ唈of᠗tate)ᨼ The ሴove cณࠆfragmě wȊl cሊਆ pk0ँx–kwL.Ke ⼦☦ tȞes kxoSgKo actuሊਵ sࠃdȃg ሃythȃg ŏtᰈ ംre (ȃ thࠆЗuሊ ᔒsࠣ whĕംthoЌ ą LinЂ0 Ke ംth U㜸_㤿ᴇ, ⼦☦ pሕkࠌᜆwȊl be sࠃd). Onਵ ሢtࠉ thࠆsࠕo̓ Lx Lȃui0 Ke ȗ caਊࠓ, wȌh U㜸_COR܆ሃd state=0, ö pሕkࠌ ȗ sࠃt ŏtᰈ ംrࠠ Ker̈l ȞᘊࠞࠃtሌȎ̩ whĕЗȃg UD㡂CORK, pk☉Lx–kwL et passes MSG_MOᴾ to ဦऋ00xᄏrkN NKe . ImpleḈntation detail: UDP_CORK iᜆnot in glibc-headeआ (/uᜉ/include/netinet/udp.hᨼ 㔎u need to add in 㔎ur pऎgraḩ #define UDP_CORK UDP_ENCAP ᜎc༈t option. Foआuᜒge with IPSEC. Uᜈd, for eԒmple, in ipᜈc-toolᜠ Note: UDP_ENCAP doeᜆnot appear 㔈t in the Ḓn page of udp ᠶDP_CORK doeᜆappeaच. Nฌࠆtᰒt thࠉࠆarࠆother sต༈t ถtȎns ሌ the SOłSOCܾT ਈᐈਆജȕᰆyค căget/set ฃ UDP sต༈ts: for exሞpਈ, S㽂N㽂CHECK ؘఎ disableؕhecksum؎nضDP؉eᔈiᐈ) (see AppendiԆE). SO_DONTROUTE (equivalent to MSG_DONTROU⨾ in send(). The SO_DONTROUTE option tellᜆ䀓on't ᜈnd ᐂa a gateway, onl㔆ᜈnd to diईctl㔆connected hoᜌᜠ” Adding: ᜈtᜎckopt᠗, SOL_SOCKET, SO_DONTROUTE, ᐒl, ᜂ唈of᠎neᨚ 堆0ᨆ And ᜈnding the pac༈t to a hoᜌ on a different network will cauᜈ “Networ༆iᜆunईachable” erऎr to be receiᐈd. ENETUNREACH The ᜒḈ will happen when MSG_DONTROUTE flag iᜆset in ą–k i܈ SO_SNDBUF. getᜎckopt(ᜣ SOL_SOCKET, SO_SNDBUF, (void *) &ᜃdbufᨠ Suppoᜈ we want to ईceiᐈ ICMP eउorᜆwith the UDP client exaḖle (li༈ ICMP deᜌination unईachable/port unईachableᨠ How can we achieᐈ thiᜆ? Fiगt, we should set thiᜆᜎc༈t option: inఆᐒl=1; seగockopఘᜣ S㼁_ⴸ, .H/q71P7qq ,(char*)&ᐒl,ؗi唈of(val)); Thẹ wࠆshคਓ add a caਊ to ሆmࠌᰎd lȏe this fฉ rࠕeȔȃg errฉ mࠗsሐes: ȃt ईᔔ_ࠉघȃt s) ȃt ईs; ᔜar ᔴТ[5⼥]; stऄᔌ ȎᐈᔆȎᐼ stऄᔌ ḗလdआmsg; stऄᔌ ᔞsgᰓआ䬕ḗg; stऄᔌ soᔏ䈈xtendࠓ_ࠉआ*࠼ stऄᔌ ȕḖhdआȕḖh; stऄᔌ soᔏሓdr䈂n tሉget; foआ(;;) Ȏv.iด_㐒sࠆ䔆&ȕḖh; Ȏv.iด_ਈ̆ = si唈of᠂cḖhᨼ ḗg.ḗg_nሞe = (voȓ*ᩑtaऐࠌ; ḗg.ḗg_nሞeਈ̆= sɕࠎf(tሉဈtᨼ ḗg.ḗg_Ȏv = &Ȏv; ḗg.ḗg_Ȏvlࠃ 䔆⼼ ḗg.ḗg_flሐs = 0; ḗg.ḗg_ᔎntऎl = ᔴuf; ḗg.ḗg_ᔎntऎlਈn = sɕࠎf(cbufᨼ ईs = ईᔔḗg᠗, &ḗg, MSG_ERᵞUE㘾 | MSG䉆AITAāᨼ Ȣ ᠉es<0) ᔎ̌ȃu࠼ foआ(cḗg = CMSG_FIᴛTℷᴘ&ḗယ;cḗg; ᔞsg =CMSG䈋XTH㜝ᡑḗg, ᔞsgᨚ Ȣ (cmsg-䐕ḗ၂lࠔࠊ =䔆SOłIP) Ȣ (cmsg-䐕ḗ၂t㔖ࠆ=䔆IP_ᴾ㤻ERᴚ ᘉintfᡒgฌ IP䈝ECVEᴝ Ḉssagࡓn"ᨼ ࠆ= ᠗tऄᔌ soᔏ䈈Ԍended䈈उ䬚CMSG䈷ATA(cmsgᨼ Ȣ ᠈) if ᠈->ࠈ䈎ंgȃ =䔆SO䈾E䈿ᴭGIN䈭CMPᨆ{ stऄᔌ sต༒ddूin 䬗ȃ = ᠗tऄᔌ sต༒ddूin *ᨘࡐ⼚; Ȣ ( ᠈->ࠈ䈌㔖ࠆ=䔆I㤺P䈷EST_UଝEACℚ && ᠈-䐈ࡂcodࠆ=䔆 I㤺P䈸ORT䈶NᴾACHᨆ) pंntf("㜈stinatiฃ ᘎऌ unईሕhሴਈ\͒ᨼ udp_ᜈndmᜐ() pk0ँx–kwL. (ᜌrЕt ༂ตb *Ȏᔴ, strЕt sต༆ *s༣ strЕt msghጉ *msg, sɕe_t ਈ̚ Sâty chࠕ༗ ĭ p༦rLԑkwL.Ke2 The dࠗtȃatȎ̆U㜸 ᘎrt mЗt nฌ be 0. If we tr㔆dࠗtȃatȎn port of ☆wࠆgࠌ EINVAL ࠉrฉ as a rࠌЉ̆vሊuࠆย pk☉LxᄏwL.Ke The destination UDP is embedded inside the msghdr parameter (In faᔌ, msg->msg_name represents a sockaddr_in; vx /:gNo iᜆsoᔏaddr_in is the destination port number). MSG_OO䠆ȗ thࠆo̊y Ȋਈgሊ f਒g fฉ UDP. RࠌЉns EOPିTSUPP ࠉrฉ Ȣ such a f਒g ȗ pሗᜈd. (ฃਵ permittࠓ tฆSO㤇䈛TᴾAM) MSG_OO䠆ȗ aਗฆȊਈgሊ ȃ AF_UNI䤠 OOB stሃ጗ fฉ “Out Of Bሃd data”. The Mᭇ䈿O䠆f਒ဆȗ pࠉmȌted ȃ T㤸. It enables sending one b㔌e of data in urgent mode. (telnet , “ctrl/c” for example). The dࠗtȃatȎ̆mЗt bࠆeȌher: ᜖eᔂfied in the msghdr (the 5Ἂ field in msghdr). Or the socket is conneᔌed. ᜏ⡄sགᜌate =䔆TCP_ESTABLISHED Notice that though this is UDP, we uᜈ ⨹P semantiᔗ here. ᬈndingؖac༈ts inضDP (contd) Ĭcasࠆthࠆsต༈t ȗ nฌ cฃ̈ctࠓ, we shoЊd fȃd ሆrคte to Ȍ; thȗ ȗ dö by ᔒਊȃg ဦrlip xंp 0p rcሂℇedt ĬcasࠆȌ is cฃ̈cted, we ЗࠆthࠆroЌe from thࠆsตk ( LuएL ःNnox member ย ᜏ, whȕh ȗ ሃ ȃstሃcࠆof tkL अ– l5 ). 䘜en the ̂––x̆Ke system ᔒll was invo༈d, g0yrkN N.lNwrni––x̆Ke find the route b㔆 g0rlip xr̂––x̆Ke and ᜈt ĄU>LЉkĆrnN̎x in LЉkL rą Ke Mดȃg thࠆpሕkࠌ tฆLስࠉ ㈆(IP ਒yࠉ) ȗ dฃࠆ by g0rN00ԑkr་ NKed 3–t8bq@twȤထ.t oxt0ଃux t it㸋5xlt1tခt༂–xt Hဆot ဦधpxpԉ(wဆKe ⠎N =Lt oxtkgccxlx–̅tWt M㬫tkȅLt–i toN–༒xtclN.wx– ଆဂ–ht ဦrଦ0x–kएN ଇe tkiԁtoNᄏህtclN.wx– ଆဂᄓ 8bqtoN–kaxLtclN.wx– N gi–tg–taNᤅltydt,it–it–xxkt cilt g0rN00x–krkN NKe dt ဦr✖xpxr᠍ဆKetခtK–ଆplNሒ5etNtLဍ0ህltwx oikd Basȕሊਵ ജሌ the pk0rą–kwL.Ke method dจs ȗ: Fȃds tᰈ rคte for the pሕ༈t by ဦrlip xंp 0p rcሂℇe Se̓s thࠆᘒckࠌ wȌᰆ g0rainNarip KĄSe Asynchronous ⴮O Therࠆis support for As㔃chrฃคs I/O ĭUDP sต༈tᜠ Thȗ meሃᜆthat ȃstࠒd of pชਂ̐ tฆ༃ญ Ȣ thࠉࠆȗ dሌሆ(b㔆 Lxህn Ke , fฉ ࠅampਈ), tᰈ ༈r̈ਆse̓s ሆ SIGIO sȐnሊ ȃ ᜄch ሆcasࠠ Usȃg A᜵̕hrฃคᜆI/O UDP ȃ ሆusࠉ spacࠆ ሖᘊȕatȎn ȗ dฃe ȃ thrࠈ stሐࠗ: 1) Adding a SIGIO signal handler b㔆calling Lg.Nn gi–Ke system ᔒll 2) Calling c̑ aKe with F_SETO䘋 and the pid of our proᔈss to tell the proᔈss that it is the owner of the ᜎᔏet (so that SIGIO signalᜆwill be delivered to it). Seᐈral pऎce᜗eᜆcan access a ᜎc༈t. If we will not call c̑ a܈ with F_SETOWN, there can be aḴiguit㔆aᜆto which pऎce᜗ will get the SIGIO signal. FoआeԒmple, if we call foए᠚ the owner of the SIGIO iᜆthe paईnt; but we can call, in the ᜎn, fcntl᠗,F_SETOWN, getpid() ). 3) Setting flags: ᔒlling fᔃtl() with F_SETFL and O_NONBLOCK | FASYNC. Ĭtᰈ ᬭGIO ha̓ਈr, ഈ caਊ lxnAcliwKed 4(Nw0ህ2 Ćlp̆tĂ̄Nkklrg–tĂpl̅h Ćlp̆tĐ.N̆gi–toN–kaxਜ ĂpਃxdĐ–rcNഐaᤌ;tvDr3/48h ĂpਃxdĐ–r0iਆttt㰌o i–Lܚ))ࠜ ĂpਃxdĐ–rNkkldĉNkklt㰌o i–aܲ/vVVOrv/fࠜt ąl␣inux t;tĂ̄x KvDr3/48@t,7bIrVTOv⤟tmࠜ Sg–k܁xਤ,īx @܁ lp̆tLīNkklGe“Ăpਃx@Đ䄅ic܁ lp̆t ĂnЋkkਉg–ࠈh oN–kaxldċroN–kaxlt㰌,3T37BN–kaxlh Đ.cgaaą ݀oN–kaxldċrwNĄࠜ oN–kaxldċrcaN.Č;tmh Đ.N̆gi–ܣ3T37@t“oN–kaxl@tmeh c̑ a܁xlA,īx @Dr,487-/@t.x 0gkKࠈh c̑ a܁xlA,īx @Dr,48DE@t7r/7/6E7bItXtDv,f/beh 8oxtcn– a܈tHog̎tą Č oxtt7r/7/6E7bItXtDv,f/btcaN.Č g–␂uxČ Ă̄rcNę–̇e tg–t–x sĂ̄x ď itNkkt oxtĂ̄x d 8oxt 9(-(h:Ngtlxoሓ tഅ oiktHgaatSxt̋aaxktHox–t oxਅtgČ kN NtKĐ–̅tNt,3T37tĐ.–NatHNČ.x–x਋ xkࠌhtg tĎipakt̋aat lx̤ഁ.܈d Appendixو : Rgd–lo̐:oxg vn Rgdᄊฃg:oxg ᐃhmn:NgฐdgtM .Hn:ଐogdgtn3R4u/.HinLVnᐐ጑lฃg:ฅg vM IP_TOS IP䈪TL IP_ℷᴭହL IP䈿PTIONS IP_ᴿUTEᵂAľRT IP_ᴾCVOPTS IP_ᴾTOPTS IP䈸KTIଽO IP_PKTOPTIONS IP_MTU䈷ISCOVER IP_ᴾ㤻ERR IP_ᴾCVTTL IP_ᴾ㤻TOS IP_MTU IP_FREEBIND IP_IPSEC_POLI㥎 IP_XFᴺ䈸OLICY IP_PASSSEC IP_TᴤNSPAREପ ଎te: FoआBSD ᔎḖatȴȊȌ㔆thࠉe is IP_ᴾCVRETOPTS ᠍hȕh ȗ ȓࠃtȕaਆto IP_ᴾTOPTSᨠ AF_UଭX: SO_PASSCRE㜆fฉ AF䈶NIX soᔏࠌs. ଎tࠩFฉ histฉȕaਆ ईሗons thesࠆ soᔏࠌ oᘌȎ̗ ሉe sᘈᔂfȈd wȌh a SOL䈛OCKET t㔖e ࠔen thคလ the㔆aई PF_UଭX sᘈcȢiᔠ U㜸: U㜸_COᴇ ᠭPPᴿTO䈶DP ਈvࠊᨠ ᴤW: ICMP_FILTER TCP: TCP䈹Oᴇ TCP䈷EFEᵂACCEPT TCP䈭ଽO TCP䈇EEPCNT TCP䈇EEPIDľ TCP䈇EEPINTVL TCP䈁IେEᴥ TCP䈺AXSEG TCP䈋ODEĤY TCP䉞UI㤇ACK TCP䈛YହNT TCP䉆IଷOW_CĤMP AF_PACKET PACKET䈤D㝂MEMBEᴛℭP PACKET䈷ᴿP䈺EMBEᴛℭP Rg጑lฃg:ฅg vnTgଃᐐdᄊฃtl᠊tM SO_㜾B㙇 SO_ᴾUSEAD㜝 SO_TYPE SO_EᴝOR SO_㜿NTRO㘪E SO_BᴿA㜹AST SO_SଷBUF SO_ᴹVBUF SO_SଷBUFFOᴹE SO_ᴹVBUFFOᴹE SO_KEEPALIVE SO_OOBINĭNE SO_ି䈹ℾCK SO_PᴭOᴭTY SO_ĭେER SO_BS㜹OMPAT Appendixع: ،cpؕlienఆ #inᔊuገ 堢ᔃtਠ᱄ #inᔊuገ 堗tdਂ㐠h> #inᔊuገ 堈उnภh> #inᔊuገ 堗tdȎ.h> #inᔊuገ 堗tंnဠh> #inᔊuገ 堗㔗/sendfȊe.᱄ #inᔊuገ 堗㔗/stሌ.᱄ #inᔊuገ 堗㔗/t㔖ࠗ.᱄ #inᔊuገ 堄nistd.᱄ #inᔊuገ 堒खሮȃet.h> ȃt Ḓȃ᠚ tcp ᔊienఆ-ؕonఓ. stऄᔌ soᔏሓdr䈂n sa; ȃt sd 䔆sockࠌ(PF_INET, SOCK䈛TᴾAM, 0ᨼ Ȣ (sd堦) pंntf("ࠉऎ॒ᨼ Ḉḗetᡑsሣ ☣ si唈of᠗tऄᔌ sต༒dጉ䈂̚ᨼ sሠsin䈢ሞiਵ 䔆AF䈭ାT; sሠsin䈖ฉt = htฃsᠱ5㈚; ȃࠌ䈒tฃᡒ⼧2.168.0.121",&sሠsȃ䈒ddच; Ȣ (cฃneᔌ᠗ጣ ᠗tऄᔌ soᔏሓdोᩑsሣ sizeย᠗ሚ)<0ᨆ{ pࠉऎघ"ᔎn̈ᔌ"ᨼ eԂtᠦᨼ ᔊos࠘sጚ; tcp ᔊienఆ-ؕonఓ. If on the other ᜂde (192.168.0.121 in thiᜆexaḖle) there iᜆno TCP ᜈऔeआliᜌening on thiᜆpoऌ ᠱ53ᨆ㔎u will get thiᜆeउor for the ᜎc༈t(ᨆ᜵ᜌem call: connect: Connection refuᜈd. You can send data on thiᜆᜎc༈t by adding, for eԒmple: conᜌ chaआ*me᜗age = 刞㔞e᜗age刼 int length; length = ᜌऊen᠞e᜗age)倯; reᜆ䔆write᠗d, Ḉ᜗age, length); wंte(ᨆiᜆthe ᜒme as ᜈnd᠚, but with no flags. AppendixطةحCMP options Thesࠆሉe ICMP optȎns yoІcሃ sࠌ wȌh sࠌsตkถt ฃ RAW I㤺P sตkࠌ: (seࠆ /Зr/ȃc਄de/nࠌȃࠌ/Ȗ_ȕmp.h) ICMP_ECHOREPLY ICMP_DEST_UNREACH ICMP_SOURCE_QUENCH ICMP_REDIRECT ICMP_ECHO ICMP_TI㨾_EXCEEDED ICMP_PARAMETERPROB ICMP_TI㨾STAMP ICMP_TI㨾STAMPREPLY ICMP_INFO_REQUEST ICMP_INFO_REPLY ICMP_ADDRESS ICMP_ADDRESSREPLY A㠸ENDIXؾ:آlags ∎r send/receive MSG_OOB MSG_PEEK MSG_DONTROUTE MSG_TRYHARD ⠆S㔃on㔞 foआ㨛G_DONTROUTE foआDECnet MSG_CTRUNC MSG_PROBE - Do not ᜈnd. Onl㔆probe path f.e. foआMTU MSG_TRUNC MSG_DONTWAIT - Nonbloc༂ng io MSG_EOR - End of ईcord MSG_WAITALL - Wait foआa full requeᜌ MSG_FIN MSG_SYN MSG_CONFIRM - ConfirḆpath ᐒlidit㔆 MSG_RST MSG_ERRQUEUE ⠆Fetch me᜗age fऎm erऎr queue MSG_NOSIGNAL ⠆Do not generate SIGPIPE MSG_㨿RE 0Ա000 ⠆Sendeआwill ᜈnd Ḏre. EԒmple: setؒnd geఆan؎ption Thȗ sȞpਈ eԒḖlࠆdࠞonstऒtࠗ hoആto sࠌ ሃd ဈt an IP lስer ถtȎn: #inᔊuገ 堗tdȎ.h> #inᔊuገ 堒खሮȃet.h> #inᔊuገ 堗㔗/t㔖ࠗ.᱄ #inᔊuገ 堗㔗/soᔏࠌ.h> #inᔊuገ 堗tंnဠh> ȃt Ḓȃ᠚ ȃt s; ȃt ถt; ȃt ईs; ȃt ฃe = 1; ȃt sɕe = sɕeย(ถtᨼ s 䔆sตketᠤF䈭ାT, SOCK䈷GRAM, ☚; Ȣ (s堦) pࠉऎघ"sตket"ᨼ ईs = sࠌsต༎pt(s, SOłIP, IP䈝ECVEᴝ, &ฃࠣ sɕeย(one)ᨼ Ȣ (ईs=䔨⼚ pࠉऎघ"sࠌsoᔏถt"); ईs = getsต༎pt᠗, SOłIP, IP䈝ECVEᴝ,&ถt,&sɕeᨼ Ȣ (ईs=䔨⼚ pࠉऎघ"getsoᔏถt"ᨼ ᘉintfᡒoᘌ 䔆娓\n",oᘌᨼ ᔊos࠘sᨼ Example: ؉ecord؉ouఈ؎pంon ThiᜆeԒmple ᜜owᜆhow to ᜈnd a ईcoओ ऎute option. #definࠆଝOUTES 9 ȃt Ḓȃ᠚ ȃt s; ȃt ถtਈn=0; stऄᔌ soᔏሓdr䈂n tሉget; ȃt ईs; ᔜar गpሕe[3+ⱋଝOUTES倯]; ᔜar buf[⼦]; taऐࠌ.sȃ_faḂl㔆= AF䈭ାT; taऐࠌ.sȃ_ᘎऌ=htฃs(9✧ᨼ ȃࠌ䈒tฃᡒ⼧Ⱐ✦.⼠5",&tሉget.sin䈒ddच; stकᘵᠴТ,"messagࠆ⼩"ᨼ s 䔆sตketᠤF䈭ାT, SOCK䈷GRAM, ☚; Ȣ (s堦) pࠉऎघ"sตket"ᨼ Ḉḗet᠉sᘒce, ☣ sɕeย᠉sᘒᔈᨚ; गpሕ࡜0] = IPOPT䈋OP; गpሕ࡜⽐IPOPT䈿PTVAL] 䔆IPOPT_ᴝ; गpሕ࡜⽐IPOPT䈿LEଢ଼ = sɕࠎf(rsᘒᔈᨨ⼼ गpሕ࡜⽐IPOPT䈿FFSET] = IPOPT䈺IିFF; ถtlࠃ=Ⱖ; Ȣ (sࠌsต༎ᘌ᠗, IPPᴿTO_IP, IP䈿PTIONS, गpሕe, sɕࠎf᠉spሕeᨚ堦) pࠉऎघ"ईᔎओ routࡓn"ᨼ eԂtᠥᨼ AP㠾NDIXؽ: UDP؈rrorᜆ Running : cat /pऎc/net/ᜃḖ | grep Udp: will giᐈ ᜎḈthing li༈: Udp: InDatagऒmᜆNoPoऌᜆInEउoग OutDatagऒmᜆRcvbufEउoग SndbufEउoग Udp: 2625 1 0 2100 0 0 InEउoग - (UDP_㨭B_INERRORSᨆ RcᐴufEउoग – UDP_MIB_RCVBUFERRORS: IncreḈnted in rrpk0r9pxpxrਃ␉ĄS܈ (net/ipv4/udp.cᨠ SndbufEउorᜆ– ᠶDP_MIB_SNDBUFERRORS) IncreḈnted in pk0rą–kഁ.܈ Anฌher mࠌrȕ: cat /proc/net/udp The last column in: drops Repईᜈntᜆᜏ-䐗གdऎpᜠ Incईmented in __udp_queue_कᑂᜏb(ᨆ net/ipv4/udp.c Whĕጎ RcᐴufErऎrs occuआ? The total nuḴer of b㔌es queued in ᜏ_receiᐈ_queue queue of a ᜎc༈t iᜆᜏ⡄ᜏ_rḈm_alloc. The total allowed meḎव of a ᜎc༈t is ᜏ⡄sགकᐴuf. It can be ईtrieᐈd with getᜎc༎pt᠚ uᜂng SO_RCVBUF. Each timࠆሆpac༈t ȗ rࠕeȔed, thࠆ >ᜏ_rḈm_alloc ȗ ȃᔉࠞࠃtࠓ by skb->truࠗɕࠩ ᜏb-䐌rueᜂ唈 it the ᜂ唈 ᠂n b㔌es) allocated foआthe data of the ᜏb pluᜆthe ᜂze of ᜏ_buff ᜌऄctuई itᜈlf. ThiᜆincreḈntation iᜆdone in ᜏb_ᜈt_owner_घ) ... atoḂc_add᠗༴⡄tऄeᜂ唈, &ᜏ-䐗གrḈm_allocᨼ ... ᜈe: include/net/ᜎc༠h When the pac༈t iᜆfईed b㔆༢ईe_ᜏb(ᨣ we decईḈnt Lu2 ☁urofxfrNllin b㔆 Lu.┦ ocxLK⨅ ; thiᜆiᜆdone in Ă̄rਕlxx ᠚: ᜎcགrfईe᠚ ... atoḂc_ᜄb᠗༴⡄tऄeᜂze, &ᜏ⡄ᜏ_rḈm_allocᨼ ... ImḈdiatel㔆in the beginning of ᜎcགqueue_कᑂs༴᠚, we haᐈ thiᜆchec༩ if ᠒tomic_ईadᡑᜏ⡄ᜏ_ञem_alloc) 倆ᜏb⡄tऄesi唈 䑅 (unᜂgned)ᜏ⡄sགकᐴufᨆ{ eउ 䔆-ENO㨾M; Whĕrࠌur̂̐ -㸋OM㸺 , tᰂs nฌifȈs thࠆ cሊlࠉ tฆdrถ thࠆᘒckࠌ. This is done in rrpk0r9pxpxrl̤rLЛKe method: stሌȕ ȃt _䈄dᙂquࠄࡂrᔔ_s༴(stऄᔌ sต༆*s༣ stऄᔌ sགbuff *s༴) ... Ȣ (᠉c = soᔏ䈫uࠄe䈉ᔔ_s༴᠗k, s༴)ᨆ< ☚ { /䬆Nฌࠆtᰒt ሃ ENOMEM eउฉ ȗ ᔜaऐࠓ tംᔈ 䬮 Ȣ (क =䔆-EିMEMᨆ{ U㜸_INC䈛TATS_BH᠗ตགnet᠗༚, U㜸_MIB_ᴹVB㘽ERᴿᴛ, ȗ_udpਂteᨼ ሌพiᕂȃᔘ&s༨䐗k_dऎpsᨼ The dࠢሄlt sɕࠆof ᜏ⡄ᜏ_कᐴuf is SK_RMEM_MAX sy᜕tੂrmem_mህ). It ࠫВਗ to (sɕࠎf(strЕt sགbТf) + ┙6) * ┙6 Seࠩ ᬇ_ᴺ㸺_MA䤆dࠢîtiฃ ĭ ̈t/cor࠮ᜎck.c Thȗ cሃ be vȈwed ሃd modȢȈd 㐵: s0li̗ęė–x ŝlxslwxwrkxcNpa entry. getᜎᔏopt()/ᜈtsoᔏopt() with R4/q1PD-; Foआthe ᜈnd queue ܁ЉHਐ xr9pxpxࠟtHxtoN␅tg–t g0rN00x–krkN N܈ tNt̋aat it Ă̄rNaaỉą–krĄSKe @tHog̎t xAx– pNaaᤌg–␂uxČ Ă̄rNaaỉLx–kr0LЛ܈dt 3–tĂ̄rNaaỉLx–kr0LЛ܈@tHxt0xci਍t ogČ̎x̄2 ddd gct܋ iഐ̉lxNkK“ĄU䐁ЉHഅഉNaaït䈌Lж䐁ЉL–kSpce ddd 3ctg tgČ lpx@tx␅ਙ og–.tgČcg–xdt 3ct–i @tHxtx–ktHg otą g–.t 9hRqrm94pRrph9ImR5 tN–kt R41r/w4RHs17 tcaN.Ltict oxtĂ̄x 2 ą rSg ܣ7bIrv,f/br/7,qvb4@t“ĄU䐁ЉĂ̄x 㙄caN.Ĉh ą rSg ܣ7bIr/7,qvb4@t“Ą㙄ĄrĂ̄x U䐕aN.Ĉh 3–t pk0rą–kwĠ܈ @tHxt̎x̄t oxt,7bIr/7,qvb4tcaN.dt3ctg tgČ ą @tHxtg–̊xഅ– t oxtMVqr:36r,/V6MD4OO7O,t̂p– xld ĂnЉNaaỉą–kr0ĄS܈ t̋aaČt ĄSrLx riH–xਉH܈d 3–t ĄSrą riH–xlrH܈ @tHxtoNAx2 ddd N iwg̉NkkKĄS㙄 ਖxĐ”x@t“Ą㙄LurHwxഉNaaïh ddd -ox–t oxt0N̄x tgČcਅxktSᤌЕਅxrLЛ܈@tHxtkx̊xwx– t ĄrHwxഉNaain@tg–tĂ̄rHclxxKࠌwx oik2 Ă̄rHclxxKe ddd N iഐ̉ĖSKĄS㙄 ਖxĐ䄅@t“Ą㙄ĄrHഅwrNaaïh ddd Tips To find out ᜎc༈t uᜈd b㔆a pऎce᜗: lᜆ-l /pऎc/[pid]/fd|grep ᜎc༈t|cut -d: ⠢3|ᜈd 'ᜮ\[//;ᜮ\]//' The numbeआretuःed iᜆthe inode numbeआof the ᜎc༈t. Infoञation about theᜈ ᜎc༈tᜆcan be obtained from netᜌat -ae After ᜌaऌing a proce᜗ which createᜆa ᜎc༈t, 㔎u can see that the inode cache waᜆincremented b㔆one b㔩 moई /pऎc/ᜊabinfo | gईp ᜎck ᜎcགinode_cache 476 485 768 5 1 : tunableᜆ 0 0 0 : ᜊabdata 97 97 0 The fiगt nuḴer, 476, iᜆthe nuḴer of actiᐈ objectᜠ END ⨜an༆㔎u! ऒmȉoᜈ@gmaȊ.ᔎm