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

From: David Laight <David.Laight@ACULAB.COM>
To: 'Kees Cook' <keescook@chromium.org>, Sargun Dhillon <sargun@sargun.me>
Cc: Christian Brauner <christian.brauner@ubuntu.com>,
	"containers@lists.linux-foundation.org" 
	<containers@lists.linux-foundation.org>,
	Giuseppe Scrivano <gscrivan@redhat.com>,
	Robert Sesek <rsesek@google.com>,
	Chris Palmer <palmer@google.com>, Jann Horn <jannh@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Matt Denton <mpdenton@google.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	Tejun Heo <tj@kernel.org>, Al Viro <viro@zeniv.linux.org.uk>,
	"cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	"David S . Miller" <davem@davemloft.net>
Subject: RE: [PATCH v3 1/4] fs, net: Standardize on file_receive helper to move fds across processes
Date: Fri, 12 Jun 2020 15:55:14 +0000	[thread overview]
Message-ID: <b598484958d140fc9f523e200490b942@AcuMS.aculab.com> (raw)
In-Reply-To: <202006120806.E770867EF@keescook>

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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