Change the cap_rights_t type from uint64_t to a structure that we can extend

in the future in a backward compatible (API and ABI) way.

The cap_rights_t represents capability rights. We used to use one bit to
represent one right, but we are running out of spare bits. Currently the new
structure provides place for 114 rights (so 50 more than the previous
cap_rights_t), but it is possible to grow the structure to hold at least 285
rights, although we can make it even larger if 285 rights won't be enough.

The structure definition looks like this:

	struct cap_rights {
		uint64_t	cr_rights[CAP_RIGHTS_VERSION + 2];
	};

The initial CAP_RIGHTS_VERSION is 0.

The top two bits in the first element of the cr_rights[] array contain total
number of elements in the array - 2. This means if those two bits are equal to
0, we have 2 array elements.

The top two bits in all remaining array elements should be 0.
The next five bits in all array elements contain array index. Only one bit is
used and bit position in this five-bits range defines array index. This means
there can be at most five array elements in the future.

To define new right the CAPRIGHT() macro must be used. The macro takes two
arguments - an array index and a bit to set, eg.

	#define	CAP_PDKILL	CAPRIGHT(1, 0x0000000000000800ULL)

We still support aliases that combine few rights, but the rights have to belong
to the same array element, eg:

	#define	CAP_LOOKUP	CAPRIGHT(0, 0x0000000000000400ULL)
	#define	CAP_FCHMOD	CAPRIGHT(0, 0x0000000000002000ULL)

	#define	CAP_FCHMODAT	(CAP_FCHMOD | CAP_LOOKUP)

There is new API to manage the new cap_rights_t structure:

	cap_rights_t *cap_rights_init(cap_rights_t *rights, ...);
	void cap_rights_set(cap_rights_t *rights, ...);
	void cap_rights_clear(cap_rights_t *rights, ...);
	bool cap_rights_is_set(const cap_rights_t *rights, ...);

	bool cap_rights_is_valid(const cap_rights_t *rights);
	void cap_rights_merge(cap_rights_t *dst, const cap_rights_t *src);
	void cap_rights_remove(cap_rights_t *dst, const cap_rights_t *src);
	bool cap_rights_contains(const cap_rights_t *big, const cap_rights_t *little);

Capability rights to the cap_rights_init(), cap_rights_set(),
cap_rights_clear() and cap_rights_is_set() functions are provided by
separating them with commas, eg:

	cap_rights_t rights;

	cap_rights_init(&rights, CAP_READ, CAP_WRITE, CAP_FSTAT);

There is no need to terminate the list of rights, as those functions are
actually macros that take care of the termination, eg:

	#define	cap_rights_set(rights, ...)				\
		__cap_rights_set((rights), __VA_ARGS__, 0ULL)
	void __cap_rights_set(cap_rights_t *rights, ...);

Thanks to using one bit as an array index we can assert in those functions that
there are no two rights belonging to different array elements provided
together. For example this is illegal and will be detected, because CAP_LOOKUP
belongs to element 0 and CAP_PDKILL to element 1:

	cap_rights_init(&rights, CAP_LOOKUP | CAP_PDKILL);

Providing several rights that belongs to the same array's element this way is
correct, but is not advised. It should only be used for aliases definition.

This commit also breaks compatibility with some existing Capsicum system calls,
but I see no other way to do that. This should be fine as Capsicum is still
experimental and this change is not going to 9.x.

Sponsored by:	The FreeBSD Foundation

1 files changed, 3 insertions, 6 deletions

diff --git a/sys/sys/filedesc.h b/sys/sys/filedesc.h
index 9f73915b8faa..968ceffe9ffa 100644
--- a/sys/sys/filedesc.h
+++ b/sys/sys/filedesc.h
@@ -33,6 +33,7 @@
 #ifndef _SYS_FILEDESC_H_
 #define	_SYS_FILEDESC_H_
 
+#include <sys/caprights.h>
 #include <sys/queue.h>
 #include <sys/event.h>
 #include <sys/lock.h>
@@ -108,10 +109,6 @@ struct filedesc_to_leader {
 
 #ifdef _KERNEL
 
-#include <sys/systm.h>	/* CTASSERT() */
-
-CTASSERT(sizeof(cap_rights_t) == sizeof(uint64_t));
-
 /* Flags for do_dup() */
 #define	DUP_FIXED	0x1	/* Force fixed allocation. */
 #define	DUP_FCNTL	0x2	/* fcntl()-style errors. */
@@ -163,13 +160,13 @@ struct	filedesc *fdshare(struct filedesc *fdp);
 struct filedesc_to_leader *
 	filedesc_to_leader_alloc(struct filedesc_to_leader *old,
 	    struct filedesc *fdp, struct proc *leader);
-int	getvnode(struct filedesc *fdp, int fd, cap_rights_t rights,
+int	getvnode(struct filedesc *fdp, int fd, cap_rights_t *rightsp,
 	    struct file **fpp);
 void	mountcheckdirs(struct vnode *olddp, struct vnode *newdp);
 void	setugidsafety(struct thread *td);
 
 /* Return a referenced file from an unlocked descriptor. */
-int	fget_unlocked(struct filedesc *fdp, int fd, cap_rights_t needrights,
+int	fget_unlocked(struct filedesc *fdp, int fd, cap_rights_t *needrightsp,
 	    int needfcntl, struct file **fpp, cap_rights_t *haverightsp);
 
 /* Requires a FILEDESC_{S,X}LOCK held and returns without a ref. */