{"id":100548,"date":"2021-06-20T10:22:54","date_gmt":"2021-06-20T08:22:55","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/uyazvimost-v-yadre-linux-zatragivayushhaya-setevoj-protokol-can-bcm"},"modified":"2021-06-20T10:22:54","modified_gmt":"2021-06-20T08:22:55","slug":"uyazvimost-v-yadre-linux-zatragivayushhaya-setevoj-protokol-can-bcm","status":"publish","type":"post","link":"https:\/\/prohoster.info\/sk\/blog\/news\/uyazvimost-v-yadre-linux-zatragivayushhaya-setevoj-protokol-can-bcm","title":{"rendered":"Zranite\u013enos\u0165 v jadre Linux, ktor\u00e1 ovplyv\u0148uje sie\u0165ov\u00fd protokol CAN BCM","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

V jadre Linux bola zisten\u00e1 zranite\u013enos\u0165 (CVE-2021-3609), ktor\u00e1 umo\u017e\u0148uje miestnemu pou\u017e\u00edvate\u013eovi zv\u00fd\u0161i\u0165 svoje pr\u00e1va v syst\u00e9me. Probl\u00e9m je sp\u00f4soben\u00fd prete\u010den\u00edm stavu pri implement\u00e1cii protokolu CAN BCM a prejavuje sa vo verzi\u00e1ch jadra Linux od 2.6.25 po 5.13-rc6. V distrib\u00faci\u00e1ch probl\u00e9m zatia\u013e zost\u00e1va neopravn\u00fd (RHEL, Fedora, Debian, Ubuntu, SUSE, Arch). <\/p>\n

V\u00fdskumn\u00edk, ktor\u00fd zistil zranite\u013enos\u0165, dok\u00e1zal pripravi\u0165 exploit na z\u00edskanie pr\u00e1v root na syst\u00e9moch s jadrami Linux 5.4 a nov\u0161\u00edmi, vr\u00e1tane preuk\u00e1zania mo\u017enosti \u00faspe\u0161n\u00e9ho vykonania \u00fatoku v Ubuntu 20.04.02 LTS. Nie je vyl\u00fa\u010den\u00e1 mo\u017enos\u0165 \u00fapravy exploitu pre star\u0161ie jadr\u00e1 (v jadre 5.4 bol k\u00f3d CAN BCM (net\/can\/bcm.c) prelo\u017een\u00fd z hrtimer_tasklet na HRTIMER_MODE_SOFT). <\/p>\n

Protokol CAN BCM umo\u017e\u0148uje registrova\u0165 vlastn\u00fd spracovate\u013e spr\u00e1v prich\u00e1dzaj\u00facich cez zbernicu CAN (controller area network) a pripoji\u0165 ho k ur\u010dit\u00e9mu sie\u0165ov\u00e9mu socketu. Po pr\u00edchode prich\u00e1dzaj\u00facej spr\u00e1vy sa vyvol\u00e1va funkcia bcm_rx_handler(). \u00dato\u010dn\u00edk m\u00f4\u017ee vyu\u017ei\u0165 prete\u010denie stavu a dosiahnu\u0165 uzavretie sie\u0165ov\u00e9ho socketu s\u00fa\u010dasne s vykon\u00e1van\u00edm bcm_rx_handler(). Pri uzavret\u00ed socketu sa vyvol\u00e1va funkcia bcm_release(), v ktorej sa uvo\u013e\u0148uje pam\u00e4\u0165 pridelen\u00e1 pre \u0161trukt\u00fary bcm_op a bcm_sock, ktor\u00e9 sa st\u00e1le pou\u017e\u00edvaj\u00fa v e\u0161te prebiehaj\u00facom spracovate\u013eovi bcm_rx_handler(). Vznik\u00e1 situ\u00e1cia, ktor\u00e1 vedie k pr\u00edstupu k u\u017e uvo\u013enen\u00e9mu bloku pam\u00e4te (use-after-free). <\/p>\n

\u00datok spo\u010d\u00edva v otvoren\u00ed dvoch socketov CAN BCM a ich pripojen\u00ed k rozhraniu vcan. V prvom socketu sa vykon\u00e1va volanie sendmsg() s pr\u00edznakom RX_SETUP na nastavenie spracovate\u013ea prich\u00e1dzaj\u00facich spr\u00e1v CAN, zatia\u013e \u010do v druhom socketu sa vykon\u00e1va volanie sendmsg() na odoslanie spr\u00e1vy do prv\u00e9ho socketu. Po pr\u00edchode spr\u00e1vy sa sp\u00fa\u0161\u0165a volanie bcm_rx_handler(), a \u00fato\u010dn\u00edk si vyberie spr\u00e1vny okamih a uzavrie prv\u00fd socket, \u010do vedie k spusteniu bcm_release() a uvo\u013eneniu \u0161trukt\u00far bcm_op a bcm_sock, hoci pr\u00e1ca bcm_rx_handler() e\u0161te nie je dokon\u010den\u00e1. <\/p>\n

Manipul\u00e1ciou s obsahom bcm_sock m\u00f4\u017ee \u00fato\u010dn\u00edk predefinova\u0165 ukazovate\u013e na funkciu sk->sk_data_ready(sk), presmerova\u0165 vykon\u00e1vanie a pomocou techn\u00edk orientovan\u00fdch na n\u00e1vrat (ROP - Return-Oriented Programming) dosiahnu\u0165 prepisovanie parametra modprobe_path a zabezpe\u010di\u0165 vykon\u00e1vanie svojho k\u00f3du s pr\u00e1vami root. Pri pou\u017eit\u00ed techniky ROP \u00fato\u010dn\u00edk nesna\u017e\u00ed sa umiestni\u0165 svoj k\u00f3d do pam\u00e4te, ale operuje u\u017e existuj\u00facimi kusmi strojov\u00fdch in\u0161trukci\u00ed v na\u010d\u00edtan\u00fdch kni\u017eniciach, ktor\u00e9 kon\u010dia in\u0161trukciou na n\u00e1vrat riadenia (v\u00e4\u010d\u0161inou ide o konce kni\u017eni\u010dn\u00fdch funkci\u00ed). \u010cinnos\u0165 exploit sa z\u00fa\u017ei na vytvorenie re\u0165azca volan\u00ed podobn\u00fdch blokov (\u201egad\u017eetov\u201c) na z\u00edskanie po\u017eadovanej funk\u010dnosti.

\"Zranite\u013enos\u0165<\/center> <\/p>\n

Na \u00fatok je potrebn\u00fd pr\u00edstup na vytv\u00e1ranie socketov CAN a nastaven\u00e9 sie\u0165ov\u00e9 rozhranie vcan. Potrebn\u00e9 opr\u00e1vnenia na uskuto\u010dnenie \u00fatoku m\u00f4\u017ee z\u00edska\u0165 nepriviligovan\u00fd pou\u017e\u00edvate\u013e v kontajneroch vytv\u00e1ran\u00fdch v syst\u00e9moch s aktivovanou podporou priestorov menn\u00fdch identifik\u00e1torov (user namespaces). Napr\u00edklad, user namespaces s\u00fa predvolene zapnut\u00e9 v Ubuntu a Federe, ale nie s\u00fa aktivovan\u00e9 v Debiane a RHEL.
\n
Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u0412 \u044f\u0434\u0440\u0435 Linux \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c (CVE-2021-3609), \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0449\u0430\u044f \u043b\u043e\u043a\u0430\u043b\u044c\u043d\u043e\u043c\u0443 \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u044e \u043f\u043e\u0434\u043d\u044f\u0442\u044c \u0441\u0432\u043e\u0438 \u043f\u0440\u0438\u0432\u0438\u043b\u0435\u0433\u0438\u0438 \u0432 \u0441\u0438\u0441\u0442\u0435\u043c\u0435. \u041f\u0440\u043e\u0431\u043b\u0435\u043c\u0430 \u0432\u044b\u0437\u0432\u0430\u043d\u0430 \u0441\u043e\u0441\u0442\u043e\u044f\u043d\u0438\u0435\u043c \u0433\u043e\u043d\u043a\u0438 \u0432 \u0440\u0435\u0430\u043b\u0438\u0437\u0430\u0446\u0438\u0438 \u043f\u0440\u043e\u0442\u043e\u043a\u043e\u043b\u0430 CAN BCM \u0438 \u043f\u0440\u043e\u044f\u0432\u043b\u044f\u0435\u0442\u0441\u044f \u0432 \u0432\u044b\u043f\u0443\u0441\u043a\u0430\u0445 \u044f\u0434\u0440\u0430 Linux \u0441 2.6.25 \u043f\u043e 5.13-rc6. \u0412 \u0434\u0438\u0441\u0442\u0440\u0438\u0431\u0443\u0442\u0438\u0432\u0430\u0445 \u043f\u0440\u043e\u0431\u043b\u0435\u043c\u0430 \u043f\u043e\u043a\u0430 \u043e\u0441\u0442\u0430\u0451\u0442\u0441\u044f \u043d\u0435\u0438\u0441\u043f\u0440\u0430\u0432\u043b\u0435\u043d\u043d\u043e\u0439 (RHEL, Fedora, Debian, Ubuntu, SUSE, Arch). \u0412\u044b\u044f\u0432\u0438\u0432\u0448\u0438\u0439 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c \u0438\u0441\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u044c \u0441\u043c\u043e\u0433 \u043f\u043e\u0434\u0433\u043e\u0442\u043e\u0432\u0438\u0442\u044c \u044d\u043a\u0441\u043f\u043b\u043e\u0438\u0442 \u0434\u043b\u044f \u043f\u043e\u043b\u0443\u0447\u0435\u043d\u0438\u044f \u043f\u0440\u0430\u0432 root […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":100549,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-100548","post","type-post","status-publish","format-standard","has-post-thumbnail","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\udd47Zranite\u013enos\u0165 v jadre Linuxu, ovplyv\u0148uj\u00faca sie\u0165ov\u00fd protokol CAN BCM | ProHoster","description":"V jadre Linuxu bola zisten\u00e1 zranite\u013enos\u0165 (CVE-2021-3609), ktor\u00e1 umo\u017e\u0148uje lok\u00e1lnemu pou\u017e\u00edvate\u013eovi zv\u00fd\u0161i\u0165 svoje privil\u00e9gi\u00e1 v 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