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Date:   Fri, 12 Jun 2020 15:55:14 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kees Cook' <keescook@...omium.org>,
        Sargun Dhillon <sargun@...gun.me>
CC:     Christian Brauner <christian.brauner@...ntu.com>,
        "containers@...ts.linux-foundation.org" 
        <containers@...ts.linux-foundation.org>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Robert Sesek <rsesek@...gle.com>,
        Chris Palmer <palmer@...gle.com>, Jann Horn <jannh@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Matt Denton <mpdenton@...gle.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: RE: [PATCH v3 1/4] fs, net: Standardize on file_receive helper to
 move fds across processes

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

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