RE: [PATCH v3 1/4] fs, net: Standardize on file_receive helper to move fds across processes

David Laight
2020-06-12T15:55:21Z

From: Kees Cook
> Sent: 12 June 2020 16:13
...
> > /* Fixed size ioctls. Can be converted later on? */
> > switch (cmd) {
> > case SECCOMP_IOCTL_NOTIF_RECV:
> > return seccomp_notify_recv(filter, buf);
> > case SECCOMP_IOCTL_NOTIF_SEND:
> > return seccomp_notify_send(filter, buf);
> > case SECCOMP_IOCTL_NOTIF_ID_VALID:
> > return seccomp_notify_id_valid(filter, buf);
> > }
> >
> > /* Probably should make some nicer macros here */
> > switch (SIZE_MASK(DIR_MASK(cmd))) {
> > case SIZE_MASK(DIR_MASK(SECCOMP_IOCTL_NOTIF_ADDFD)):
>
> Ah yeah, I like this because of what you mention below: it's forward
> compat too. (I'd just use the ioctl masks directly...)
>
> switch (cmd & ~(_IOC_SIZEMASK | _IOC_DIRMASK))

Since you need the same mask on the case labels I think
I'd define a helper just across the switch statement:

#define M(cmd) ((cmd & ~(_IOC_SIZEMASK | _IOC_DIRMASK))
switch (M(cmd)) {
case M(SECCOMP_IOCTL_NOTIF_RECV):
...
}
#undef M

It is probably wrong to mask off DIRMASK.
But you might need to add extra case labels for
the broken one(s).

Prior to worries about indirect jumps you could
get a dense set of case label and faster code.

David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)