Date:	Fri, 25 Jul 2014 14:47:11 +0100
From:	David Drysdale <drysdale@...gle.com>
To:	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Meredydd Luff <meredydd@...atehouse.org>,
	Kees Cook <keescook@...omium.org>,
	James Morris <james.l.morris@...cle.com>,
	Andy Lutomirski <luto@...capital.net>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Paul Moore <paul@...l-moore.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-api@...r.kernel.org, David Drysdale <drysdale@...gle.com>
Subject: [PATCH 4/6] cap_rights_limit.2: limit FD rights for Capsicum

Signed-off-by: David Drysdale <drysdale@...gle.com>
---
 man2/cap_rights_limit.2 | 241 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 241 insertions(+)
 create mode 100644 man2/cap_rights_limit.2

diff --git a/man2/cap_rights_limit.2 b/man2/cap_rights_limit.2
new file mode 100644
index 000000000000..450bbdc6f86d
--- /dev/null
+++ b/man2/cap_rights_limit.2
@@ -0,0 +1,241 @@
+.\"
+.\" Copyright (c) 2008-2010 Robert N. M. Watson
+.\" Copyright (c) 2012-2013 The FreeBSD Foundation
+.\" Copyright (c) 2013-2014 Google, Inc.
+.\" All rights reserved.
+.\"
+.\" %%%LICENSE_START(BSD_2_CLAUSE)
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\" %%%LICENSE_END
+.\"
+.TH CAP_RIGHTS_LIMIT 2 2014-05-07 "Linux" "Linux Programmer's Manual"
+.SH NAME
+cap_rights_limit \- limit Capsicum capability rights
+.SH SYNOPSIS
+.nf
+.B #include <sys/capsicum.h>
+.sp
+.BI "int cap_rights_limit(int " fd ", const struct cap_rights *" rights ,
+.BI "                     unsigned int " fcntls ,
+.BI "                     int " nioctls ", unsigned int *" ioctls );
+.SH DESCRIPTION
+When a file descriptor is created by a function such as
+.BR accept (2),
+.BR accept4 (2),
+.BR creat (2),
+.BR epoll_create (2),
+.BR eventfd (2),
+.BR mq_open (2),
+.BR open (2),
+.BR openat (2),
+.BR pdfork (2),
+.BR pipe (2),
+.BR pipe2 (2),
+.BR signalfd (2),
+.BR socket (2),
+.BR socketpair (2)
+or
+.BR timerfd_create (2),
+it implicitly has all Capsicum capability rights.
+Those rights can be reduced (but never expanded) by using the
+.BR cap_rights_limit ()
+system call.
+Once Capsicum capability rights are reduced, operations on the file descriptor
+.I fd
+will be limited to those permitted by the remainder of the arguments.
+.PP
+The
+.I rights
+argument describes the primary rights for the file descriptor, as a
+.I cap_rights
+structure:
+.in +4n
+.nf
+
+#define CAP_RIGHTS_VERSION_00	0
+#define CAP_RIGHTS_VERSION_01	1
+#define CAP_RIGHTS_VERSION_02	2
+#define CAP_RIGHTS_VERSION_03	3
+#define CAP_RIGHTS_VERSION	CAP_RIGHTS_VERSION_00
+struct cap_rights {
+    __u64    cr_rights[CAP_RIGHTS_VERSION + 2];
+};
+.fi
+.in
+.PP
+The contents of the
+.I cr_rights
+array are encoded as follows.
+.IP \(bu
+The top 2 bits of
+.I cr_rights[0]
+hold the array size minus 2, allowing for an array size between 2 and 5 inclusive.
+.IP \(bu
+The top 2 bits of the other
+.I cr_rights
+entries are zero.
+.IP \(bu
+The following 5 bits of each array entry indicate its position in the array,
+from 0b00001 for entry [0], 0b00010 for entry [1], up to 0b10000 for entry [4].
+.IP \(bu
+The remaining 57 bits of each array entry identify a particular primary
+right.
+.PP
+This encoding allows for future expansion in the number of distinct rights;
+for example, a
+.I cap_rights
+structure holding the
+.B CAP_READ
+and
+.B CAP_BINDAT
+rights would have contents of
+.in +4n
+.nf
+0x0200000000000001 0x0400000000001000
+.fi
+.in
+as a version 0 array, but would be encoded in a larger version 1 array as
+.in +4n
+.nf
+0x4200000000000001 0x0400000000001000 0x0800000000000000.
+.fi
+.in
+.PP
+User programs should prepare the contents of the
+.I cap_rights
+structure with the
+.BR cap_rights_init (3)
+family of functions.
+The complete list of primary rights can be found in the
+.BR rights (7)
+manual page.
+.PP
+If a file descriptor is granted the
+.B CAP_FCNTL
+primary capability right, some specific
+.BR fcntl (2)
+commands can be selectively disallowed with the
+.I fcntls
+argument.  The following flags may be specified in the
+.I fcntls
+argument for this:
+.TP
+.B CAP_FCNTL_GETFL
+Permit
+.B F_GETFL
+command.
+.TP
+.B CAP_FCNTL_SETFL
+Permit
+.B F_SETFL
+command.
+.TP
+.B CAP_FCNTL_GETOWN
+Permit
+.B F_GETOWN
+command.
+.TP
+.B CAP_FCNTL_SETOWN
+Permit
+.B F_SETOWN
+command.
+.PP
+A value of
+.B CAP_FCNTL_ALL
+for the
+.I fcntls
+argument leaves the set of allowed
+.BR fcntl (2)
+commands unchanged.
+.PP
+However, note that
+.BR fcntl (2)
+commands that are analogous to other system calls
+(such as
+.B F_DUPFD
+or
+.BR F_GETPIPE_SZ )
+are not controlled by the
+.B CAP_FCNTL
+right and so do not have corresponding values in the
+.I fcntls
+argument.
+.PP
+If a file descriptor is granted the
+.B CAP_IOCTL
+capability right, the list of allowed
+.BR ioctl (2)
+commands can be selectively reduced (but never expanded) using the
+.I nioctls
+and
+.I ioctls
+arguments.
+The
+.I ioctls
+argument is an array of
+.BR ioctl (2)
+command values and the
+.I nioctls
+argument specifies the number of elements in the array.
+.PP
+If the
+.I nioctls
+argument is -1 or 0, the
+.I ioctls
+argument is ignored, and either all
+.BR ioctl (2)
+operations or no
+.BR ioctl (2)
+operations (respectively) will be allowed.
+.PP
+Capsicum capability rights assigned to a file descriptor can be obtained with the
+.BR cap_rights_get (2)
+system call.
+.SH RETURN VALUE
+.BR cap_rights_limit ()
+returns zero on success. On error, -1 is returned and
+.I errno
+is set appropriately.
+.SH ERRORS
+.TP
+.B EBADF
+.I fd
+isn't a valid open file descriptor.
+.TP
+.B EINVAL
+An invalid set of rights has been requested in
+.IR rights .
+.TP
+.B ENOMEM
+Out of memory.
+.TP
+.B ENOTCAPABLE
+The arguments contain capability rights not present for the given file descriptor (Capsicum
+capability rights list can only be reduced, never expanded).
+.SH VERSION
+Capsicum support was added to the kernel in version 3.???.
+.SH SEE ALSO
+.BR cap_enter (2),
+.BR cap_rights_get (2),
+.BR cap_rights_init (3),
+.BR capsicum (7),
+.BR rights (7)
--
2.0.0.526.g5318336

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