Chiwopsezo (CVE-2021-4155) chadziwika mu kachidindo ka fayilo ya XFS yomwe imalola wogwiritsa ntchito wamba kuti awerenge deta yosagwiritsidwa ntchito molunjika kuchokera pachida chotchinga. Mitundu yonse yayikulu ya Linux kernel yakale kuposa 5.16 yomwe ili ndi dalaivala wa XFS imakhudzidwa ndi nkhaniyi. Kukonzekeraku kudaphatikizidwa mu mtundu wa 5.16, komanso zosintha za kernel 5.15.14, 5.10.91, 5.4.171, 4.19.225, ndi zina. Mkhalidwe wa zosintha zomwe zikupangidwira kukonza vutoli pakugawa zitha kutsatiridwa pamasamba awa: Debian, RHEL, SUSE, Fedora, Ubuntu, Arch.
Kusatetezeka kumadza chifukwa cha machitidwe olakwika a XFS-specific ioctl(XFS_IOC_ALLOCSP) ndi ioctl(XFS_IOC_FREESP), omwe ndi ofanana ndi kernel-wide fallocate() system call. Mukakulitsa kukula kwa fayilo komwe sikuli kolumikizana ndi block, ioctls XFS_IOC_ALLOCSP/XFS_IOC_FREESP musakhazikitsenso ma byte amchira kukhala ziro mpaka malire a block. Chifukwa chake, pa XFS yokhala ndi block block size ya 4096 byte, wowukira amatha kuwerenga mpaka ma 4095 bytes a data yolembedwa m'mbuyomu kuchokera ku block iliyonse. Maderawa atha kukhala ndi data kuchokera pamafayilo ochotsedwa, mafayilo osungidwa, ndi mafayilo okhala ndi midadada yochotsedwa.
Mutha kuyesa dongosolo lanu pavutoli pogwiritsa ntchito njira yosavuta yochitira. Ngati, mutatha kutsata malamulo omwe akufunsidwa, ndizotheka kuwerenga zolemba za Shakespeare, ndiye kuti dalaivala wa FS ali pachiwopsezo. Poyambirira kuyika gawo la XFS kuti ziwonetsedwe kumafuna mwayi woyambira.
Popeza ioctl(XFS_IOC_ALLOCSP) ndi ioctl(XFS_IOC_FREESP) ndi ofanana mu magwiridwe antchito monga muyezo fallocate(), ndipo kusiyana kwawo kokha ndi kutayikira deta, kupezeka kwawo n'kofanana ndi backdoor. Ngakhale lamulo lachidziwitso losasintha mawonekedwe omwe alipo mu kernel, malinga ndi Linus, adaganiza zochotseratu ma ioctls awa mumtundu wotsatira.
Source: opennet.ru