{"id":183605,"date":"2026-10-05T10:54:21","date_gmt":"2026-10-05T08:54:21","guid":{"rendered":"https:\/\/prohoster.info\/blog\/news\/teo-de-raadt-predlozhil-izmeneniya-dlya-ogranicheniya-dostupa-k-fs-cherez-funkcziyu-openat"},"modified":"2026-10-05T10:54:25","modified_gmt":"2026-10-05T08:54:25","slug":"theo-de-raadt-proposed-changes-to-restrict-filesystem-access-via-openat","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/news\/theo-de-raadt-proposed-changes-to-restrict-filesystem-access-via-openat","title":{"rendered":"Theo de Raadt navrhl zm\u011bny pro omezen\u00ed p\u0159\u00edstupu k FS pomoc\u00ed funkce openat","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Theo de Raadt navrhl zahrnout do OpenBSD nov\u00fd mechanismus pro sn\u00ed\u017een\u00ed povrchu \u00fatoku, realizovan\u00fd prost\u0159ednictv\u00edm roz\u0161\u00ed\u0159en\u00ed schopnost\u00ed syst\u00e9mov\u00e9ho vol\u00e1n\u00ed openat. Patche s implementac\u00ed dodate\u010dn\u00fdch p\u0159\u00edznak\u016f pro openat a open, kter\u00e9 omezuj\u00ed mo\u017enost p\u0159echodu k nad\u0159azen\u00fdm adres\u00e1\u0159\u016fm p\u0159es \u201a\/..\u2018 a p\u0159\u00edstupy pomoc\u00ed absolutn\u00edch cest, byly p\u0159ipraveny pro j\u00e1dro, libc a tak\u00e9 n\u011bkter\u00e9 aplikace z z\u00e1kladn\u00edho syst\u00e9mu. Zm\u011bny zat\u00edm nebyly za\u0159azeny do OpenBSD-current a jsou ve f\u00e1zi diskuze mezi v\u00fdvoj\u00e1\u0159i. <\/p>\n

Rodina syst\u00e9mov\u00fdch vol\u00e1n\u00ed openat(2) funguje jako analog open(2) s t\u00edm rozd\u00edlem, \u017ee pokud je v parametru \u201apath\u2018 uvedena relativn\u00ed cesta, otev\u00edran\u00fd soubor je ur\u010den vzhledem k adres\u00e1\u0159i spojen\u00e9mu s file descriptor \u201afd\u2018, a ne vzhledem k aktu\u00e1ln\u00edmu pracovn\u00edmu adres\u00e1\u0159i. Pokud p\u0159ed\u00e1te openat absolutn\u00ed cestu, nap\u0159\u00edklad: int dirfd = open(\u2018\/tmp\u2019, O_RDONLY | O_DIRECTORY); int hfd = openat(dirfd, \u2018\/etc\/hosts\u2019, O_RDONLY); <\/p>\n

Funkce openat() ignoruje \u201adirfd\u2018 a v d\u016fsledku toho bude absolutn\u00ed cesta zpracov\u00e1na b\u011b\u017en\u00fdm zp\u016fsobem. <\/p>\n

Proto samotn\u00e1 v\u00fdm\u011bna open() za openat() nezvy\u0161uje bezpe\u010dnost programu. Takov\u00e9 vol\u00e1n\u00ed m\u016f\u017ee urychlit anal\u00fdzu cesty, ale neomezuje p\u0159\u00edstup k souborov\u00e9mu syst\u00e9mu. Zaji\u0161t\u011bn\u00ed ochrany nezaru\u010duj\u00ed ani p\u0159\u00edznaky, kter\u00e9 zakazuj\u00ed absolutn\u00ed cesty (nap\u0159\u00edklad RESOLVE_BENEATH a\/nebo RESOLVE_IN_ROOT pro openat2 v Linuxu): program\u00e1tor je mus\u00ed p\u0159id\u00e1vat ke v\u0161em vhodn\u00fdm vol\u00e1n\u00edm, a p\u0159i p\u0159evzet\u00ed kontroly nad procesem m\u016f\u017ee \u00fato\u010dn\u00edk vyu\u017e\u00edt jin\u00fdch cest pro otev\u00edr\u00e1n\u00ed soubor\u016f. <\/p>\n

P\u0159i pr\u00e1ci na utilit\u011b openrsync se Theo dostal do situace, kdy pot\u0159eboval omezit jej\u00ed mo\u017enosti obej\u00edt souborov\u00fd syst\u00e9m, ale nebylo mo\u017en\u00e9 to prov\u00e9st pomoc\u00ed funkc\u00ed unveil() a pledge(). Pak vznikla my\u0161lenka na mechanismus podobn\u00fd openat(), ale se zabezpe\u010dovac\u00edmi vlastnostmi dopl\u0148uj\u00edc\u00edmi pledge\/unveil nebo dokonce funguj\u00edc\u00edmi i v jejich nep\u0159\u00edtomnosti. <\/p>\n

Hlavn\u00ed my\u0161lenkou je u\u010dinit omezen\u00ed sou\u010d\u00e1st\u00ed samotn\u00e9ho deskriptoru adres\u00e1\u0159e. K tomu je navrhov\u00e1n p\u0159\u00edznak F_BELOW, kter\u00fd lze nastavit p\u0159es fcntl(), nebo p\u0159\u00edznak O_BELOW pro open(). Omezen\u00fd t\u00edmto zp\u016fsobem deskriptor \u201adirfd\u2018 bude povolovat pouze p\u0159echody dol\u016f po stromu adres\u00e1\u0159\u016f: vol\u00e1n\u00ed openat() s absolutn\u00ed cestou nebo s p\u0159echodem nahoru p\u0159es \u201a..\u2018 budou kon\u010dit chybou ENOENT. V p\u0159\u00edpad\u011b \u00fatoku vedouc\u00edho k vykon\u00e1v\u00e1n\u00ed k\u00f3du bude tabulka souborov\u00fdch deskriptor\u016f procesu obsahovat m\u00e9n\u011b funk\u010dn\u00ed \u201adirfd\u2018, co\u017e omez\u00ed povrch \u00fatoku.
\n
Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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\u0418\u0437\u043c\u0435\u043d\u0435\u043d\u0438\u044f \u043f\u043e\u043a\u0430 […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":10,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-183605","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\n","aioseo_head_json":{"title":"\ud83e\udd47Theo de Raadt navrhl zm\u011bny pro omezen\u00ed p\u0159\u00edstupu k F\u0421 p\u0159es funkci openat | ProHoster","description":"Theo de Raadt navrhl za\u0159adit do OpenBSD nov\u00fd mechanismus pro sn\u00ed\u017een\u00ed \u00fato\u010dn\u00e9 plochy, realizovan\u00fd prost\u0159ednictv\u00edm roz\u0161\u00ed\u0159en\u00ed schopnost\u00ed 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