Re: [PATCH 1/1] userfaultfd: require CAP_SYS_PTRACE for UFFD_FEATURE_EVENT_FORK

On Tue, Nov 5, 2019 at 7:29 AM Mike Rapoport [off-list ref] wrote:

Current implementation of UFFD_FEATURE_EVENT_FORK modifies the file
descriptor table from the read() implementation of uffd, which may have
security implications for unprivileged use of the userfaultfd.

Limit availability of UFFD_FEATURE_EVENT_FORK only for callers that have
CAP_SYS_PTRACE.

Thanks. But shouldn't we be doing the capability check at
userfaultfd(2) time (when we do the other permission checks), not
later, in the API ioctl?