Kotsi (CVE-2021-4155) e khethiloe ka har'a khoutu ea tsamaiso ea faele ea XFS e lumellang mosebedisi ea se nang tokelo ea sebakeng seo ho bala data ea thibela e sa sebelisoang ka ho toba ho sesebelisoa sa block. Liphetolelo tsohle tse kholo tsa Linux kernel tsa khale ho feta 5.16 tse nang le mokhanni oa XFS li angoa ke taba ena. Tokiso e kenyellelitsoe ho mofuta oa 5.16, hammoho le lintlafatsong tsa kernel 5.15.14, 5.10.91, 5.4.171, 4.19.225, joalo-joalo. Boemo ba lintlafatso tse hlahisoang ho lokisa bothata kabong bo ka lateloa maqepheng ana: Debian, RHEL, SUSE, Fedora, Ubuntu, Arch.
Kotsi e bakoa ke boitšoaro bo fosahetseng ba XFS-specific ioctl(XFS_IOC_ALLOCSP) le ioctl(XFS_IOC_FREESP), e leng analogue e sebetsang ea kernel-wide fallocate() system call. Ha o eketsa boholo ba faele e sa tsamaisaneng le li-block, ioctls XFS_IOC_ALLOCSP/XFS_IOC_FREESP ha e tsosolose li-byte tsa mohatla ho zero ho fihlela moeli oa block o latelang. Ka hona, ho XFS e nang le boholo ba block block ea 4096 bytes, mohlaseli a ka bala ho fihlela ho 4095 bytes ea data e ngotsoeng e fetileng ho tloha ho thibela ka 'ngoe. Libaka tsena li kanna tsa ba le data ho tsoa ho lifaele tse hlakotsoeng, lifaele tse senyehileng, le lifaele tse nang le li-blocks tse felisitsoeng.
U ka leka sistimi ea hau bakeng sa bothata ka ho sebelisa mohlala o bonolo oa tšebeliso. Haeba, ka mor'a ho phethahatsa tatellano e reriloeng ea litaelo, ho ka khoneha ho bala mongolo oa Shakespeare, joale mokhanni oa FS o kotsing. Qalong ho kenya karohano ea XFS bakeng sa pontšo ho hloka litokelo tsa motso.
Kaha ioctl(XFS_IOC_ALLOCSP) le ioctl(XFS_IOC_FREESP) li batla li ts'oana ka ts'ebetso joalo ka fallocate e tloaelehileng (), mme phapang ea bona feela ke ho lutla ha data, boteng ba bona bo ts'oana le backdoor. Ho sa tsotellehe leano le akaretsang la ho se fetole li-interfaces tse teng kernel, ka tlhahiso ea Linus, ho ile ha etsoa qeto ea ho tlosa li-ioctls tsena ka ho feletseng phetolelong e latelang.
Source: opennet.ru