{"id":121189,"date":"2024-12-31T15:46:00","date_gmt":"2024-12-31T13:46:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/kollizii-v-sokrashhyonnyh-identifikatorah-kommitov-v-yadre-linux"},"modified":"2024-12-31T15:46:00","modified_gmt":"2024-12-31T13:46:00","slug":"kollizii-v-sokrashhyonnyh-identifikatorah-kommitov-v-yadre-linux","status":"publish","type":"post","link":"https:\/\/prohoster.info\/sk\/blog\/news\/kollizii-v-sokrashhyonnyh-identifikatorah-kommitov-v-yadre-linux","title":{"rendered":"Kolizije u skra\u0107enim identifikatorima commit-a u Linux kernelu","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Kees Cook, b\u00fdval\u00fd hlavn\u00fd syst\u00e9mov\u00fd administr\u00e1tor kernel.org a l\u00edder Ubuntu Security Team, demon\u0161troval mo\u017enos\u0165 vytv\u00e1rania commitu, ktor\u00e9ho skr\u00e1ten\u00fd identifik\u00e1tor sa zhoduje s commitom, ktor\u00fd bol predt\u00fdm pridan\u00fd do jadra Linux. Experiment bol vykonan\u00fd ako potvrdenie \u00fa\u010delnosti prechodu na 16-znakov\u00e9 skr\u00e1ten\u00e9 identifik\u00e1tory commitov v jadre Linux, ktor\u00e9 boli predt\u00fdm diskutovan\u00e9 na zozname diskusie v\u00fdvoj\u00e1rov jadra, ale neboli schv\u00e1len\u00e9 Linusom Torvaldsom. <\/p>\n

Skr\u00e1ten\u00e9 identifik\u00e1tory commitov sa vytv\u00e1raj\u00fa ponechan\u00edm prv\u00fdch 12 znakov od hash SHA-1 (48 bitov z 160 bitov). Ke\u010f\u017ee po\u010det objektov v jadre identifikovan\u00fdch cez hash SHA-1 presiahol 13 mili\u00f3nov, vznik kol\u00edzi\u00ed pri pou\u017e\u00edvan\u00ed 12-znakov\u00e9ho prefixu sa stal ot\u00e1zkou \u010dasu. Ako pr\u00edklad s\u00fa uveden\u00e9 u\u017e pridelen\u00e9 objekty v jadre, ktor\u00e9 sa prel\u00ednaj\u00fa vo svojich 11-znakov\u00fdch identifik\u00e1toroch. Okrem toho sa spom\u00edna, \u017ee sa u\u017e v okt\u00f3bri zaznamenali kol\u00edzie 12-znakov\u00fdch identifik\u00e1torov, no pred odoslan\u00edm patchu to bolo zisten\u00e9 utilitou checkpatch. <\/p>\n

Skshortn\u00e9 identifik\u00e1tory sa pou\u017e\u00edvaj\u00fa pri publikovan\u00ed kr\u00e1tkych odkazov na commity a tie\u017e sa uv\u00e1dzaj\u00fa pri odosielan\u00ed zmien v tagu «Fixes» ako odkaz na commit, probl\u00e9m v ktorom bol vyrie\u0161en\u00fd v odoslanom patche (napr\u00edklad «Fixes: e21d2170f366»). V\u00fdskyt kol\u00edzi\u00ed, pri ktor\u00fdch je viacero r\u00f4znych zmien spojen\u00fdch s jedn\u00fdm skr\u00e1ten\u00fdm identifik\u00e1torom, m\u00f4\u017ee vies\u0165 k poru\u0161eniu funk\u010dnosti n\u00e1strojov na anal\u00fdzu a kontrolu zmien, ktor\u00e9 zoh\u013ead\u0148uj\u00fa obsah tagov «Fixes». Napr\u00edklad, tieto tagy sa zoh\u013ead\u0148uj\u00fa v spracovate\u013eovi check_fixes, ktor\u00fd sa pou\u017e\u00edva v branche linux-next, ako aj v skriptoch na anal\u00fdzu opr\u00e1v zranite\u013enost\u00ed a sledovanie \u017eivotn\u00e9ho cyklu patchov. <\/p>\n

Linus Torvalds skepticky reagoval na n\u00e1vrh zv\u00fd\u0161i\u0165 minim\u00e1lnu ve\u013ekos\u0165 skr\u00e1ten\u00fdch identifik\u00e1torov, preto\u017ee v skuto\u010dnosti je po\u010det commitov v repozit\u00e1ri v\u00fdrazne men\u0161\u00ed ako po\u010det objektov (pribli\u017ene 1\/8). Je pravdepodobn\u00e9, \u017ee ak n\u00e1hodn\u00e9 prekrytia vznikn\u00fa, tak bud\u00fa medzi commitom a objektom in\u00e9ho typu (napr\u00edklad blobom alebo vetvou). Pod\u013ea jeho n\u00e1zoru s\u00fa skr\u00e1ten\u00e9 identifik\u00e1tory navrhnut\u00e9 tak, aby boli preh\u013eadn\u00e9, \u010ditate\u013en\u00e9 a \u013eahko citovate\u013en\u00e9, a zatia\u013e neexistuj\u00fa objekt\u00edvne predpoklady na zv\u00fd\u0161enie ich ve\u013ekosti. <\/p>\n

Jeden z v\u00fdvoj\u00e1rov navrhol dosiahnu\u0165 zmen\u0161enie ve\u013ekosti pri zv\u00fd\u0161en\u00ed po\u010dtu v\u00fdznamn\u00fdch bitov pou\u017eit\u00edm nov\u00e9ho form\u00e1tu zalo\u017een\u00e9ho na k\u00f3dovan\u00ed Base36 (znaky 0-9a-z) namiesto hexadecim\u00e1lnych \u010d\u00edslic. Pod\u013ea Linusa by tak\u00e9to zmeny vytvorili viac probl\u00e9mov, ne\u017e by vyrie\u0161ili. Napr\u00edklad by bolo potrebn\u00e9 prida\u0165 podporu pre nov\u00fd form\u00e1t do existuj\u00facich util\u00edt a zavies\u0165 identifik\u00e1tor form\u00e1tu, aby sa rozl\u00ed\u0161il star\u00fd a nov\u00fd form\u00e1t. <\/p>\n

Na demon\u0161tr\u00e1ciu toho, \u017ee probl\u00e9m so skr\u00e1ten\u00fdmi identifik\u00e1tormi nie je hypotetick\u00fd a jeho rie\u0161enie sa neoplat\u00ed odklada\u0165, Kees Cook vypracoval zmenu dokument\u00e1cie jadra, skr\u00e1ten\u00fd identifik\u00e1tor ktorej (1da177e4c3f4) sa zhodoval s identifik\u00e1torom commitu na vytvorenie vetvy jadra 2.6.12-rc2. Kol\u00edziu sa podarilo n\u00e1js\u0165 za 6 hod\u00edn v\u00fdpo\u010dtov na syst\u00e9me s GPU NVIDIA GeForce RTX 3080. <\/p>\n

V\u00fdber bol vykonan\u00fd s pou\u017eit\u00edm n\u00e1stroja lucky-commit — do textu cie\u013eov\u00e9ho patche sa prid\u00e1vali n\u00e1hodn\u00e9 medzery, a\u017e k\u00fdm sa 12-znakov\u00fd prefix SHA-1 nezos\u00faladil s u\u017e existuj\u00facimi prefixmi commitov v jadre. Pod\u013ea Case predstavuj\u00fa probl\u00e9m nie n\u00e1hodn\u00e9 prekrytia, ale sk\u00f4r mo\u017enos\u0165 manipul\u00e1cie so skr\u00e1ten\u00fdmi identifik\u00e1tormi na zl\u00e9 \u00fa\u010dely, napr\u00edklad na ob\u00eddenie nejak\u00fdch kontrol.
\n
Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u041a\u0435\u0439\u0441 \u041a\u0443\u043a (Kees Cook), \u0431\u044b\u0432\u0448\u0438\u0439 \u0433\u043b\u0430\u0432\u043d\u044b\u0439 \u0441\u0438\u0441\u0442\u0435\u043c\u043d\u044b\u0439 \u0430\u0434\u043c\u0438\u043d\u0438\u0441\u0442\u0440\u0430\u0442\u043e\u0440 kernel.org \u0438 \u043b\u0438\u0434\u0435\u0440 Ubuntu Security Team, \u043f\u0440\u043e\u0434\u0435\u043c\u043e\u043d\u0441\u0442\u0440\u0438\u0440\u043e\u0432\u0430\u043b \u0432\u043e\u0437\u043c\u043e\u0436\u043d\u043e\u0441\u0442\u044c \u0441\u043e\u0437\u0434\u0430\u043d\u0438\u044f \u043a\u043e\u043c\u043c\u0438\u0442\u0430, \u0441\u043e\u043a\u0440\u0430\u0449\u0451\u043d\u043d\u044b\u0439 \u0438\u0434\u0435\u043d\u0442\u0438\u0444\u0438\u043a\u0430\u0442\u043e\u0440 \u043a\u043e\u0442\u043e\u0440\u043e\u0433\u043e \u0441\u043e\u0432\u043f\u0430\u0434\u0430\u0435\u0442 \u0441 \u043a\u043e\u043c\u043c\u0438\u0442\u043e\u043c, \u0440\u0430\u043d\u0435\u0435 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hlavn\u00fd syst\u00e9mov\u00fd administr\u00e1tor kernel.org a l\u00edder Ubuntu Security Team, demon\u0161troval mo\u017enos\u0165 vytvorenia commitu, skr\u00e1ten\u00fd identifik\u00e1tor ktor\u00e9ho sa zhoduje s predch\u00e1dzaj\u00facim commitom.","canonical_url":"https:\/\/prohoster.info\/sk\/blog\/news\/kollizii-v-sokrashhyonnyh-identifikatorah-kommitov-v-yadre-linux","robots":"max-image-preview:large","keywords":"","webmasterTools":{"miscellaneous":""},"schema":null,"og:locale":"sk_SK","og:site_name":"ProHoster | \u041a\u0443\u043f\u0438\u0442\u044c \u043d\u0430\u0434\u0435\u0436\u043d\u044b\u0439 \u0445\u043e\u0441\u0442\u0438\u043d\u0433 \u0434\u043b\u044f \u0441\u0430\u0439\u0442\u043e\u0432 \u0441 \u0437\u0430\u0449\u0438\u0442\u043e\u0439 \u043e\u0442 DDoS, VPS VDS \u0441\u0435\u0440\u0432\u0435\u0440\u044b","og:type":"article","og:title":"\ud83e\udd47\u041a\u043e\u043b\u043b\u0438\u0437\u0438\u0438 \u0432 \u0441\u043e\u043a\u0440\u0430\u0449\u0451\u043d\u043d\u044b\u0445 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