Second-to-last commit implementing Capsicum capabilities in the FreeBSD

kernel for FreeBSD 9.0:

Add a new capability mask argument to fget(9) and friends, allowing system
call code to declare what capabilities are required when an integer file
descriptor is converted into an in-kernel struct file *.  With options
CAPABILITIES compiled into the kernel, this enforces capability
protection; without, this change is effectively a no-op.

Some cases require special handling, such as mmap(2), which must preserve
information about the maximum rights at the time of mapping in the memory
map so that they can later be enforced in mprotect(2) -- this is done by
narrowing the rights in the existing max_protection field used for similar
purposes with file permissions.

In namei(9), we assert that the code is not reached from within capability
mode, as we're not yet ready to enforce namespace capabilities there.
This will follow in a later commit.

Update two capability names: CAP_EVENT and CAP_KEVENT become
CAP_POST_KEVENT and CAP_POLL_KEVENT to more accurately indicate what they
represent.

Approved by:	re (bz)
Submitted by:	jonathan
Sponsored by:	Google Inc

1 files changed, 20 insertions, 8 deletions

diff --git a/sys/kern/uipc_mqueue.c b/sys/kern/uipc_mqueue.c
index 9b334ac..e13912c 100644
--- a/sys/kern/uipc_mqueue.c
+++ b/sys/kern/uipc_mqueue.c
@@ -52,6 +52,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/systm.h>
 #include <sys/limits.h>
 #include <sys/buf.h>
+#include <sys/capability.h>
 #include <sys/dirent.h>
 #include <sys/event.h>
 #include <sys/eventhandler.h>
@@ -2087,19 +2088,19 @@ kmq_unlink(struct thread *td, struct kmq_unlink_args *uap)
 	return (error);
 }
 
-typedef int (*_fgetf)(struct thread *, int, struct file **);
+typedef int (*_fgetf)(struct thread *, int, cap_rights_t, struct file **);
 
 /*
  * Get message queue by giving file slot
  */
 static int
-_getmq(struct thread *td, int fd, _fgetf func,
+_getmq(struct thread *td, int fd, cap_rights_t rights, _fgetf func,
        struct file **fpp, struct mqfs_node **ppn, struct mqueue **pmq)
 {
 	struct mqfs_node *pn;
 	int error;
 
-	error = func(td, fd, fpp);
+	error = func(td, fd, rights, fpp);
 	if (error)
 		return (error);
 	if (&mqueueops != (*fpp)->f_ops) {
@@ -2118,21 +2119,21 @@ static __inline int
 getmq(struct thread *td, int fd, struct file **fpp, struct mqfs_node **ppn,
 	struct mqueue **pmq)
 {
-	return _getmq(td, fd, fget, fpp, ppn, pmq);
+	return _getmq(td, fd, CAP_POLL_KEVENT, fget, fpp, ppn, pmq);
 }
 
 static __inline int
 getmq_read(struct thread *td, int fd, struct file **fpp,
 	 struct mqfs_node **ppn, struct mqueue **pmq)
 {
-	return _getmq(td, fd, fget_read, fpp, ppn, pmq);
+	return _getmq(td, fd, CAP_READ, fget_read, fpp, ppn, pmq);
 }
 
 static __inline int
 getmq_write(struct thread *td, int fd, struct file **fpp,
 	struct mqfs_node **ppn, struct mqueue **pmq)
 {
-	return _getmq(td, fd, fget_write, fpp, ppn, pmq);
+	return _getmq(td, fd, CAP_WRITE, fget_write, fpp, ppn, pmq);
 }
 
 static int
@@ -2243,7 +2244,7 @@ kmq_notify(struct thread *td, struct kmq_notify_args *uap)
 	struct filedesc *fdp;
 	struct proc *p;
 	struct mqueue *mq;
-	struct file *fp;
+	struct file *fp, *fp2;
 	struct mqueue_notifier *nt, *newnt = NULL;
 	int error;
 
@@ -2267,7 +2268,18 @@ kmq_notify(struct thread *td, struct kmq_notify_args *uap)
 		return (error);
 again:
 	FILEDESC_SLOCK(fdp);
-	if (fget_locked(fdp, uap->mqd) != fp) {
+	fp2 = fget_locked(fdp, uap->mqd);
+	if (fp2 == NULL) {
+		FILEDESC_SUNLOCK(fdp);
+		error = EBADF;
+		goto out;
+	}
+	error = cap_funwrap(fp2, CAP_POLL_KEVENT, &fp2);
+	if (error) {
+		FILEDESC_SUNLOCK(fdp);
+		goto out;
+	}
+	if (fp2 != fp) {
 		FILEDESC_SUNLOCK(fdp);
 		error = EBADF;
 		goto out;