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  • Vincent Bernat's avatar
    sk-filter: Add ability to lock a socket filter program · d59577b6
    Vincent Bernat authored
    While a privileged program can open a raw socket, attach some
    restrictive filter and drop its privileges (or send the socket to an
    unprivileged program through some Unix socket), the filter can still
    be removed or modified by the unprivileged program. This commit adds a
    socket option to lock the filter (SO_LOCK_FILTER) preventing any
    modification of a socket filter program.
    This is similar to OpenBSD BIOCLOCK ioctl on bpf sockets, except even
    root is not allowed change/drop the filter.
    The state of the lock can be read with getsockopt(). No error is
    triggered if the state is not changed. -EPERM is returned when a user
    tries to remove the lock or to change/remove the filter while the lock
    is active. The check is done directly in sk_attach_filter() and
    sk_detach_filter() and does not affect only setsockopt() syscall.
    Signed-off-by: default avatarVincent Bernat <>
    Signed-off-by: default avatarDavid S. Miller <>