{"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\/cs\/blog\/news\/kollizii-v-sokrashhyonnyh-identifikatorah-kommitov-v-yadre-linux","title":{"rendered":"Kolize ve zkr\u00e1cen\u00fdch identifik\u00e1torech commit\u016f v j\u00e1d\u0159e Linux","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Kees Cook, b\u00fdval\u00fd hlavn\u00ed syst\u00e9mov\u00fd administr\u00e1tor kernel.org a vedouc\u00ed t\u00fdmu Ubuntu Security, demonstroval mo\u017enost vytvo\u0159en\u00ed commitu, jeho\u017e zkr\u00e1cen\u00fd identifik\u00e1tor se shoduje s commitem, kter\u00fd byl d\u0159\u00edve p\u0159id\u00e1n do j\u00e1dra Linux. Experiment byl proveden jako d\u016fkaz vhodnosti p\u0159echodu na 16 znakov\u00e9 zkr\u00e1cen\u00e9 identifik\u00e1tory commit\u016f v j\u00e1d\u0159e Linux, o \u010dem\u017e se ji\u017e d\u0159\u00edve diskutovalo v mailing listu v\u00fdvoj\u00e1\u0159\u016f j\u00e1dra, ale nebylo to schv\u00e1leno Linusem Torvaldsem. <\/p>\n

Zkr\u00e1cen\u00e9 identifik\u00e1tory commit\u016f se vytv\u00e1\u0159ej\u00ed ponech\u00e1n\u00edm prvn\u00edch 12 znak\u016f z hash SHA-1 (48 bit\u016f z 160 bit\u016f). Vzhledem k tomu, \u017ee po\u010det objekt\u016f v j\u00e1d\u0159e, kter\u00e9 jsou identifikov\u00e1ny pomoc\u00ed hash SHA-1, p\u0159ekro\u010dil 13 milion\u016f, stalo se vznik\u00e1n\u00ed koliz\u00ed p\u0159i pou\u017eit\u00ed 12-znakov\u00fdch prefix\u016f ot\u00e1zkou \u010dasu. Jako p\u0159\u00edklad byly uvedeny ji\u017e p\u0159idan\u00e9 objekty do j\u00e1dra, kter\u00e9 se k\u0159\u00ed\u017e\u00ed podle sv\u00fdch 11-znakov\u00fdch identifik\u00e1tor\u016f. D\u00e1le bylo zm\u00edn\u011bno, \u017ee k\u0159\u00ed\u017een\u00ed 12-znakov\u00fdch identifik\u00e1tor\u016f ji\u017e bylo zaznamen\u00e1no v \u0159\u00edjnu, ale p\u0159ed odesl\u00e1n\u00edm patch byl odhalen utilitou checkpatch. <\/p>\n

Zkr\u00e1cen\u00e9 identifik\u00e1tory se pou\u017e\u00edvaj\u00ed p\u0159i publikov\u00e1n\u00ed kr\u00e1tk\u00fdch odkaz\u016f na commity a tak\u00e9 se uv\u00e1d\u011bj\u00ed p\u0159i odes\u00edl\u00e1n\u00ed zm\u011bn v tagu «Fixes» jako odkaz na commit, v n\u011bm\u017e je probl\u00e9m vy\u0159e\u0161en v odeslan\u00e9 z\u00e1plav\u011b (nap\u0159\u00edklad «Fixes: e21d2170f366»). Vznik koliz\u00ed, kdy jsou r\u016fzn\u00e9 zm\u011bny spojeny s jedn\u00edm zkr\u00e1cen\u00fdm identifik\u00e1torem, m\u016f\u017ee v\u00e9st k poruch\u00e1m v n\u00e1stroj\u00edch pro anal\u00fdzu a kontrolu zm\u011bn, kter\u00e9 zohled\u0148uj\u00ed obsah tag\u016f «Fixes». Nap\u0159\u00edklad tyto tagy se zohled\u0148uj\u00ed v zpracovateli check_fixes, kter\u00fd se pou\u017e\u00edv\u00e1 ve v\u011btvi linux-next, a tak\u00e9 ve skriptech pro anal\u00fdzu oprav zranitelnost\u00ed a sledov\u00e1n\u00ed \u017eivotn\u00edho cyklu z\u00e1plat. <\/p>\n

Linus Torvalds byl skeptick\u00fd k n\u00e1vrhu na zv\u00fd\u0161en\u00ed minim\u00e1ln\u00ed velikosti zkr\u00e1cen\u00fdch identifik\u00e1tor\u016f, proto\u017ee ve skute\u010dnosti je po\u010det commit\u016f v repozit\u00e1\u0159i v\u00fdrazn\u011b ni\u017e\u0161\u00ed ne\u017e po\u010det objekt\u016f (p\u0159ibli\u017en\u011b 1\/8). Je pravd\u011bpodobn\u00e9, \u017ee pokud k n\u00e1hodn\u00fdm koliz\u00edm dojde, bude to mezi commitem a objektem jin\u00e9ho typu (nap\u0159\u00edklad blobem nebo v\u011btv\u00ed). Podle jeho n\u00e1zoru jsou zkr\u00e1cen\u00e9 identifik\u00e1tory zkr\u00e1cen\u00e9 pr\u00e1v\u011b proto, aby byly p\u0159ehledn\u00e9, \u010diteln\u00e9 a snadno citovateln\u00e9, a pro zv\u00fd\u0161en\u00ed jejich velikosti zat\u00edm neexistuj\u00ed objektivn\u00ed p\u0159edpoklady. <\/p>\n

Jeden z v\u00fdvoj\u00e1\u0159\u016f navrhl, aby se zmen\u0161en\u00ed velikosti dos\u00e1hlo zv\u00fd\u0161en\u00edm po\u010dtu v\u00fdznamn\u00fdch bit\u016f pomoc\u00ed nov\u00e9ho form\u00e1tu zalo\u017een\u00e9ho na k\u00f3dov\u00e1n\u00ed Base36 (znaky 0-9a-z) m\u00edsto hexadecim\u00e1ln\u00edch \u010d\u00edslic. Podle Linuse by takov\u00e1 zm\u011bna vytvo\u0159ila v\u00edce probl\u00e9m\u016f, ne\u017e by vy\u0159e\u0161ila. Nap\u0159\u00edklad by bylo nutn\u00e9 p\u0159idat podporu nov\u00e9ho form\u00e1tu do st\u00e1vaj\u00edc\u00edch utilit a zav\u00e9st identifik\u00e1tor form\u00e1tu k rozli\u0161en\u00ed mezi star\u00fdm a nov\u00fdm form\u00e1tem. <\/p>\n

Aby demonstroval, \u017ee probl\u00e9m se zkr\u00e1cen\u00fdmi identifik\u00e1tory nen\u00ed pouze teoretick\u00fd a jeho \u0159e\u0161en\u00ed by se nem\u011blo odkl\u00e1dat, Kees Cook vytvo\u0159il zm\u011bnu v dokumentaci j\u00e1dra, jej\u00ed\u017e zkr\u00e1cen\u00fd identifik\u00e1tor (1da177e4c3f4) se shodoval s identifik\u00e1torem commitu pro vytvo\u0159en\u00ed v\u011btve j\u00e1dra 2.6.12-rc2. Kolizi se poda\u0159ilo nal\u00e9zt za 6 hodin v\u00fdpo\u010dt\u016f na syst\u00e9mu s GPU NVIDIA GeForce RTX 3080. <\/p>\n

Zkou\u0161en\u00ed bylo provedeno pomoc\u00ed n\u00e1stroje lucky-commit — do textu c\u00edlov\u00e9 z\u00e1platy byly p\u0159id\u00e1v\u00e1ny n\u00e1hodn\u00e9 mezery, dokud 12-znakov\u00fd prefix SHA-1 nesouhlasil s ji\u017e existuj\u00edc\u00edmi prefixy commit\u016f v j\u00e1d\u0159e. Podle Case bude probl\u00e9mem sp\u00ed\u0161e n\u00e1hodn\u00e1 p\u0159ekryvy, ne\u017e schopnost manipulovat se zkr\u00e1cen\u00fdmi identifik\u00e1tory za \u00fa\u010delem \u0161kodliv\u00e9ho pou\u017eit\u00ed, nap\u0159\u00edklad pro obch\u00e1zen\u00ed n\u011bjak\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 \u0434\u043e\u0431\u0430\u0432\u043b\u0435\u043d\u043d\u044b\u043c \u0432 \u044f\u0434\u0440\u043e Linux. \u042d\u043a\u0441\u043f\u0435\u0440\u0438\u043c\u0435\u043d\u0442 \u043f\u0440\u043e\u0432\u0435\u0434\u0451\u043d \u0432 \u043a\u0430\u0447\u0435\u0441\u0442\u0432\u0435 \u043f\u043e\u0434\u0442\u0432\u0435\u0440\u0436\u0434\u0435\u043d\u0438\u044f \u0446\u0435\u043b\u0435\u0441\u043e\u043e\u0431\u0440\u0430\u0437\u043d\u043e\u0441\u0442\u0438 \u043f\u0435\u0440\u0435\u0445\u043e\u0434\u0430 \u043d\u0430 16-\u0441\u0438\u043c\u0432\u043e\u043b\u044c\u043d\u044b\u0435 \u0441\u043e\u043a\u0440\u0430\u0449\u0451\u043d\u043d\u044b\u0435 \u0438\u0434\u0435\u043d\u0442\u0438\u0444\u0438\u043a\u0430\u0442\u043e\u0440\u044b \u043a\u043e\u043c\u043c\u0438\u0442\u043e\u0432 \u0432 \u044f\u0434\u0440\u0435 Linux, \u0440\u0430\u043d\u0435\u0435 \u043e\u0431\u0441\u0443\u0436\u0434\u0430\u0432\u0448\u0435\u0433\u043e\u0441\u044f \u0432 \u0441\u043f\u0438\u0441\u043a\u0435 \u0440\u0430\u0441\u0441\u044b\u043b\u043a\u0438 \u0440\u0430\u0437\u0440\u0430\u0431\u043e\u0442\u0447\u0438\u043a\u043e\u0432 \u044f\u0434\u0440\u0430, \u043d\u043e \u043d\u0435 \u043e\u0434\u043e\u0431\u0440\u0435\u043d\u043d\u043e\u0433\u043e \u041b\u0438\u043d\u0443\u0441\u043e\u043c […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-121189","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47Kolize ve zkr\u00e1cen\u00fdch identifik\u00e1torech commit\u016f v j\u00e1d\u0159e Linuxu | ProHoster","description":"Kees Cook, b\u00fdval\u00fd hlavn\u00ed syst\u00e9mov\u00fd administr\u00e1tor kernel.org a vedouc\u00ed t\u00fdmu Ubuntu Security, demonstroval mo\u017enost vytvo\u0159en\u00ed commitu, jeho\u017e zkr\u00e1cen\u00fd identifik\u00e1tor se shoduje s p\u0159edchoz\u00edm commitem.","canonical_url":"https:\/\/prohoster.info\/cs\/blog\/news\/kollizii-v-sokrashhyonnyh-identifikatorah-kommitov-v-yadre-linux","robots":"max-image-preview:large","keywords":"","webmasterTools":{"miscellaneous":""},"schema":null,"og:locale":"cs_CZ","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 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