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, 12 insertions, 8 deletions

diff --git a/sys/kern/uipc_sem.c b/sys/kern/uipc_sem.c
index 917c343..82a4622 100644
--- a/sys/kern/uipc_sem.c
+++ b/sys/kern/uipc_sem.c
@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 #include "opt_posix.h"
 
 #include <sys/param.h>
+#include <sys/capability.h>
 #include <sys/condvar.h>
 #include <sys/fcntl.h>
 #include <sys/file.h>
@@ -116,7 +117,8 @@ static int	ksem_create(struct thread *td, const char *path,
 		    semid_t *semidp, mode_t mode, unsigned int value,
 		    int flags, int compat32);
 static void	ksem_drop(struct ksem *ks);
-static int	ksem_get(struct thread *td, semid_t id, struct file **fpp);
+static int	ksem_get(struct thread *td, semid_t id, cap_rights_t rights,
+    struct file **fpp);
 static struct ksem *ksem_hold(struct ksem *ks);
 static void	ksem_insert(char *path, Fnv32_t fnv, struct ksem *ks);
 static struct ksem *ksem_lookup(char *path, Fnv32_t fnv);
@@ -525,13 +527,13 @@ ksem_create(struct thread *td, const char *name, semid_t *semidp, mode_t mode,
 }
 
 static int
-ksem_get(struct thread *td, semid_t id, struct file **fpp)
+ksem_get(struct thread *td, semid_t id, cap_rights_t rights, struct file **fpp)
 {
 	struct ksem *ks;
 	struct file *fp;
 	int error;
 
-	error = fget(td, id, &fp);
+	error = fget(td, id, rights, &fp);
 	if (error)
 		return (EINVAL);
 	if (fp->f_type != DTYPE_SEM) {
@@ -623,7 +625,8 @@ ksem_close(struct thread *td, struct ksem_close_args *uap)
 	struct file *fp;
 	int error;
 
-	error = ksem_get(td, uap->id, &fp);
+	/* No capability rights required to close a semaphore. */
+	error = ksem_get(td, uap->id, 0, &fp);
 	if (error)
 		return (error);
 	ks = fp->f_data;
@@ -648,7 +651,7 @@ ksem_post(struct thread *td, struct ksem_post_args *uap)
 	struct ksem *ks;
 	int error;
 
-	error = ksem_get(td, uap->id, &fp);
+	error = ksem_get(td, uap->id, CAP_SEM_POST, &fp);
 	if (error)
 		return (error);
 	ks = fp->f_data;
@@ -738,7 +741,7 @@ kern_sem_wait(struct thread *td, semid_t id, int tryflag,
 	int error;
 
 	DP((">>> kern_sem_wait entered! pid=%d\n", (int)td->td_proc->p_pid));
-	error = ksem_get(td, id, &fp);
+	error = ksem_get(td, id, CAP_SEM_WAIT, &fp);
 	if (error)
 		return (error);
 	ks = fp->f_data;
@@ -804,7 +807,7 @@ ksem_getvalue(struct thread *td, struct ksem_getvalue_args *uap)
 	struct ksem *ks;
 	int error, val;
 
-	error = ksem_get(td, uap->id, &fp);
+	error = ksem_get(td, uap->id, CAP_SEM_GETVALUE, &fp);
 	if (error)
 		return (error);
 	ks = fp->f_data;
@@ -838,7 +841,8 @@ ksem_destroy(struct thread *td, struct ksem_destroy_args *uap)
 	struct ksem *ks;
 	int error;
 
-	error = ksem_get(td, uap->id, &fp);
+	/* No capability rights required to close a semaphore. */
+	error = ksem_get(td, uap->id, 0, &fp);
 	if (error)
 		return (error);
 	ks = fp->f_data;