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, 72 insertions, 33 deletions

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index f3f9cbc..3082aea 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -431,6 +431,26 @@ fdtofp(int fd, struct filedesc *fdp)
 	return (fp);
 }
 
+static inline int
+fdunwrap(int fd, cap_rights_t rights, struct filedesc *fdp, struct file **fpp)
+{
+
+	*fpp = fdtofp(fd, fdp);
+	if (*fpp == NULL)
+		return (EBADF);
+
+#ifdef CAPABILITIES
+	if ((*fpp)->f_type == DTYPE_CAPABILITY) {
+		int err = cap_funwrap(*fpp, rights, fpp);
+		if (err != 0) {
+			*fpp = NULL;
+			return (err);
+		}
+	}
+#endif /* CAPABILITIES */
+	return (0);
+}
+
 int
 kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
 {
@@ -489,9 +509,9 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
 
 	case F_GETFL:
 		FILEDESC_SLOCK(fdp);
-		if ((fp = fdtofp(fd, fdp)) == NULL) {
+		error = fdunwrap(fd, CAP_FCNTL, fdp, &fp);
+		if (error != 0) {
 			FILEDESC_SUNLOCK(fdp);
-			error = EBADF;
 			break;
 		}
 		td->td_retval[0] = OFLAGS(fp->f_flag);
@@ -500,9 +520,9 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
 
 	case F_SETFL:
 		FILEDESC_SLOCK(fdp);
-		if ((fp = fdtofp(fd, fdp)) == NULL) {
+		error = fdunwrap(fd, CAP_FCNTL, fdp, &fp);
+		if (error != 0) {
 			FILEDESC_SUNLOCK(fdp);
-			error = EBADF;
 			break;
 		}
 		fhold(fp);
@@ -532,9 +552,9 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
 
 	case F_GETOWN:
 		FILEDESC_SLOCK(fdp);
-		if ((fp = fdtofp(fd, fdp)) == NULL) {
+		error = fdunwrap(fd, CAP_FCNTL, fdp, &fp);
+		if (error != 0) {
 			FILEDESC_SUNLOCK(fdp);
-			error = EBADF;
 			break;
 		}
 		fhold(fp);
@@ -547,9 +567,9 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
 
 	case F_SETOWN:
 		FILEDESC_SLOCK(fdp);
-		if ((fp = fdtofp(fd, fdp)) == NULL) {
+		error = fdunwrap(fd, CAP_FCNTL, fdp, &fp);
+		if (error != 0) {
 			FILEDESC_SUNLOCK(fdp);
-			error = EBADF;
 			break;
 		}
 		fhold(fp);
@@ -573,9 +593,9 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
 	case F_SETLK:
 	do_setlk:
 		FILEDESC_SLOCK(fdp);
-		if ((fp = fdtofp(fd, fdp)) == NULL) {
+		error = fdunwrap(fd, CAP_FLOCK, fdp, &fp);
+		if (error != 0) {
 			FILEDESC_SUNLOCK(fdp);
-			error = EBADF;
 			break;
 		}
 		if (fp->f_type != DTYPE_VNODE) {
@@ -668,9 +688,9 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
 
 	case F_GETLK:
 		FILEDESC_SLOCK(fdp);
-		if ((fp = fdtofp(fd, fdp)) == NULL) {
+		error = fdunwrap(fd, CAP_FLOCK, fdp, &fp);
+		if (error != 0) {
 			FILEDESC_SUNLOCK(fdp);
-			error = EBADF;
 			break;
 		}
 		if (fp->f_type != DTYPE_VNODE) {
@@ -1312,7 +1332,7 @@ kern_fstat(struct thread *td, int fd, struct stat *sbp)
 
 	AUDIT_ARG_FD(fd);
 
-	if ((error = fget(td, fd, &fp)) != 0)
+	if ((error = fget(td, fd, CAP_FSTAT, &fp)) != 0)
 		return (error);
 
 	AUDIT_ARG_FILE(td->td_proc, fp);
@@ -1368,7 +1388,7 @@ fpathconf(struct thread *td, struct fpathconf_args *uap)
 	struct vnode *vp;
 	int error;
 
-	if ((error = fget(td, uap->fd, &fp)) != 0)
+	if ((error = fget(td, uap->fd, CAP_FPATHCONF, &fp)) != 0)
 		return (error);
 
 	/* If asynchronous I/O is available, it works for all descriptors. */
@@ -2294,7 +2314,7 @@ fget_unlocked(struct filedesc *fdp, int fd)
 #define	FGET_GETCAP	0x00000001
 static __inline int
 _fget(struct thread *td, int fd, struct file **fpp, int flags,
-    cap_rights_t needrights, cap_rights_t *haverights, u_char *maxprotp,
+    cap_rights_t needrights, cap_rights_t *haverightsp, u_char *maxprotp,
     int fget_flags)
 {
 	struct filedesc *fdp;
@@ -2369,28 +2389,36 @@ _fget(struct thread *td, int fd, struct file **fpp, int flags,
 }
 
 int
-fget(struct thread *td, int fd, struct file **fpp)
+fget(struct thread *td, int fd, cap_rights_t rights, struct file **fpp)
+{
+
+	return(_fget(td, fd, fpp, 0, rights, NULL, NULL, 0));
+}
+
+int
+fget_mmap(struct thread *td, int fd, cap_rights_t rights, u_char *maxprotp,
+    struct file **fpp)
 {
 
-	return(_fget(td, fd, fpp, 0, 0, NULL, NULL, 0));
+	return (_fget(td, fd, fpp, 0, rights, NULL, maxprotp, 0));
 }
 
 int
-fget_read(struct thread *td, int fd, struct file **fpp)
+fget_read(struct thread *td, int fd, cap_rights_t rights, struct file **fpp)
 {
 
-	return(_fget(td, fd, fpp, FREAD, 0, NULL, NULL, 0));
+	return(_fget(td, fd, fpp, FREAD, rights, NULL, NULL, 0));
 }
 
 int
-fget_write(struct thread *td, int fd, struct file **fpp)
+fget_write(struct thread *td, int fd, cap_rights_t rights, struct file **fpp)
 {
 
-	return(_fget(td, fd, fpp, FWRITE, 0, NULL, NULL, 0));
+	return (_fget(td, fd, fpp, FWRITE, rights, NULL, NULL, 0));
 }
 
 /*
- * Unlike the other fget() calls, which will accept and check capability rights
+ * Unlike the other fget() calls, which accept and check capability rights
  * but never return capabilities, fgetcap() returns the capability but doesn't
  * check capability rights.
  */
@@ -2410,13 +2438,15 @@ fgetcap(struct thread *td, int fd, struct file **fpp)
  * XXX: what about the unused flags ?
  */
 static __inline int
-_fgetvp(struct thread *td, int fd, struct vnode **vpp, int flags)
+_fgetvp(struct thread *td, int fd, int flags, cap_rights_t needrights,
+    cap_rights_t *haverightsp, struct vnode **vpp)
 {
 	struct file *fp;
 	int error;
 
 	*vpp = NULL;
-	if ((error = _fget(td, fd, &fp, flags, 0, NULL, NULL, 0)) != 0)
+	if ((error = _fget(td, fd, &fp, flags, needrights, haverightsp,
+	    NULL, 0)) != 0)
 		return (error);
 	if (fp->f_vnode == NULL) {
 		error = EINVAL;
@@ -2430,25 +2460,33 @@ _fgetvp(struct thread *td, int fd, struct vnode **vpp, int flags)
 }
 
 int
-fgetvp(struct thread *td, int fd, struct vnode **vpp)
+fgetvp(struct thread *td, int fd, cap_rights_t rights, struct vnode **vpp)
 {
 
-	return (_fgetvp(td, fd, vpp, 0));
+	return (_fgetvp(td, fd, 0, rights, NULL, vpp));
+}
+
+int
+fgetvp_rights(struct thread *td, int fd, cap_rights_t need, cap_rights_t *have,
+    struct vnode **vpp)
+{
+	return (_fgetvp(td, fd, 0, need, have, vpp));
 }
 
 int
-fgetvp_read(struct thread *td, int fd, struct vnode **vpp)
+fgetvp_read(struct thread *td, int fd, cap_rights_t rights, struct vnode **vpp)
 {
 
-	return (_fgetvp(td, fd, vpp, FREAD));
+	return (_fgetvp(td, fd, FREAD, rights, NULL, vpp));
 }
 
 #ifdef notyet
 int
-fgetvp_write(struct thread *td, int fd, struct vnode **vpp)
+fgetvp_write(struct thread *td, int fd, cap_rights_t rights,
+    struct vnode **vpp)
 {
 
-	return (_fgetvp(td, fd, vpp, FWRITE));
+	return (_fgetvp(td, fd, FWRITE, rights, NULL, vpp));
 }
 #endif
 
@@ -2464,7 +2502,8 @@ fgetvp_write(struct thread *td, int fd, struct vnode **vpp)
  * during use.
  */
 int
-fgetsock(struct thread *td, int fd, struct socket **spp, u_int *fflagp)
+fgetsock(struct thread *td, int fd, cap_rights_t rights, struct socket **spp,
+    u_int *fflagp)
 {
 	struct file *fp;
 	int error;
@@ -2472,7 +2511,7 @@ fgetsock(struct thread *td, int fd, struct socket **spp, u_int *fflagp)
 	*spp = NULL;
 	if (fflagp != NULL)
 		*fflagp = 0;
-	if ((error = _fget(td, fd, &fp, 0, 0, NULL, NULL, 0)) != 0)
+	if ((error = _fget(td, fd, &fp, 0, rights, NULL, NULL, 0)) != 0)
 		return (error);
 	if (fp->f_type != DTYPE_SOCKET) {
 		error = ENOTSOCK;
@@ -2557,7 +2596,7 @@ flock(struct thread *td, struct flock_args *uap)
 	int vfslocked;
 	int error;
 
-	if ((error = fget(td, uap->fd, &fp)) != 0)
+	if ((error = fget(td, uap->fd, CAP_FLOCK, &fp)) != 0)
 		return (error);
 	if (fp->f_type != DTYPE_VNODE) {
 		fdrop(fp, td);