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

2 files changed, 20 insertions, 2 deletions

diff --git a/sys/fs/portalfs/portal_vfsops.c b/sys/fs/portalfs/portal_vfsops.c
index a8c16c4..04e7a3d 100644
--- a/sys/fs/portalfs/portal_vfsops.c
+++ b/sys/fs/portalfs/portal_vfsops.c
@@ -40,6 +40,7 @@
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/capability.h>
 #include <sys/domain.h>
 #include <sys/filedesc.h>
 #include <sys/kernel.h>
@@ -112,7 +113,12 @@ portal_mount(struct mount *mp)
 	if (error)
 		return (error);
 
-	if ((error = fget(td, v, &fp)) != 0)
+	/*
+	 * Capsicum is not incompatible with portalfs, but we don't really
+	 * know what rights are required. In the spirit of "better safe than
+	 * sorry", pretend that all rights are required for now.
+	 */
+	if ((error = fget(td, v, CAP_MASK_VALID, &fp)) != 0)
 		return (error);
         if (fp->f_type != DTYPE_SOCKET) {
 		fdrop(fp, td);
diff --git a/sys/fs/portalfs/portal_vnops.c b/sys/fs/portalfs/portal_vnops.c
index 6fcc1ce..7cd5267 100644
--- a/sys/fs/portalfs/portal_vnops.c
+++ b/sys/fs/portalfs/portal_vnops.c
@@ -38,7 +38,10 @@
  * Portal Filesystem
  */
 
+#include "opt_capsicum.h"
+
 #include <sys/param.h>
+#include <sys/capability.h>
 #include <sys/fcntl.h>
 #include <sys/file.h>
 #include <sys/kernel.h>
@@ -232,6 +235,15 @@ portal_open(ap)
 	struct file *fp;
 	struct portal_cred pcred;
 
+#ifdef CAPABILITY_MODE
+	/*
+	 * This may require access to a global namespace (e.g. an IP address);
+	 * disallow it entirely, as we do open(2).
+	 */
+	if (IN_CAPABILITY_MODE(td))
+		return (ECAPMODE);
+#endif
+
 	/*
 	 * Nothing to do when opening the root node.
 	 */
@@ -414,7 +426,7 @@ portal_open(ap)
 	 * Check that the mode the file is being opened for is a subset
 	 * of the mode of the existing descriptor.
 	 */
-	if ((error = fget(td, fd, &fp)) != 0)
+	if ((error = fget(td, fd, 0, &fp)) != 0)
 		goto bad;
 	if (((ap->a_mode & (FREAD|FWRITE)) | fp->f_flag) != fp->f_flag) {
 		fdrop(fp, td);