| Description: | The do_umount function in fs/namespace.c in the Linux kernel through 3.17 does not require the CAP_SYS_ADMIN capability for do_remount_sb calls that change the root filesystem to read-only, which allows local users to cause a denial of service (loss of writability) by making certain unshare system calls, clearing the / MNT_LOCKED flag, and making an MNT_FORCE umount system call. Andy Lutomirski discovered that the Linux kernel was not checking the CAP_SYS_ADMIN when remounting filesystems to read-only. A local user could exploit this flaw to cause a denial of service (loss of writability).
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