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, 61 insertions, 35 deletions

diff --git a/sys/kern/uipc_syscalls.c b/sys/kern/uipc_syscalls.c
index c434973..0e5efe6 100644
--- a/sys/kern/uipc_syscalls.c
+++ b/sys/kern/uipc_syscalls.c
@@ -120,33 +120,47 @@ SYSCTL_INT(_kern_ipc, OID_AUTO, nsfbufsused, CTLFLAG_RD, &nsfbufsused, 0,
     "Number of sendfile(2) sf_bufs in use");
 
 /*
- * Convert a user file descriptor to a kernel file entry.  A reference on the
- * file entry is held upon returning.  This is lighter weight than
- * fgetsock(), which bumps the socket reference drops the file reference
- * count instead, as this approach avoids several additional mutex operations
- * associated with the additional reference count.  If requested, return the
- * open file flags.
+ * Convert a user file descriptor to a kernel file entry and check that, if
+ * it is a capability, the right rights are present. A reference on the file
+ * entry is held upon returning.
  */
 static int
-getsock(struct filedesc *fdp, int fd, struct file **fpp, u_int *fflagp)
+getsock_cap(struct filedesc *fdp, int fd, cap_rights_t rights,
+    struct file **fpp, u_int *fflagp)
 {
 	struct file *fp;
+#ifdef CAPABILITIES
+	struct file *fp_fromcap;
 	int error;
+#endif
 
 	fp = NULL;
-	if (fdp == NULL || (fp = fget_unlocked(fdp, fd)) == NULL) {
-		error = EBADF;
-	} else if (fp->f_type != DTYPE_SOCKET) {
+	if ((fdp == NULL) || ((fp = fget_unlocked(fdp, fd)) == NULL))
+		return (EBADF);
+#ifdef CAPABILITIES
+	/*
+	 * If the file descriptor is for a capability, test rights and use
+	 * the file descriptor referenced by the capability.
+	 */
+	error = cap_funwrap(fp, rights, &fp_fromcap);
+	if (error) {
 		fdrop(fp, curthread);
-		fp = NULL;
-		error = ENOTSOCK;
-	} else {
-		if (fflagp != NULL)
-			*fflagp = fp->f_flag;
-		error = 0;
+		return (error);
 	}
+	if (fp != fp_fromcap) {
+		fhold(fp_fromcap);
+		fdrop(fp, curthread);
+		fp = fp_fromcap;
+	}
+#endif /* CAPABILITIES */
+	if (fp->f_type != DTYPE_SOCKET) {
+		fdrop(fp, curthread);
+		return (ENOTSOCK);
+	}
+	if (fflagp != NULL)
+		*fflagp = fp->f_flag;
 	*fpp = fp;
-	return (error);
+	return (0);
 }
 
 /*
@@ -226,7 +240,7 @@ kern_bind(td, fd, sa)
 	int error;
 
 	AUDIT_ARG_FD(fd);
-	error = getsock(td->td_proc->p_fd, fd, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, fd, CAP_BIND, &fp, NULL);
 	if (error)
 		return (error);
 	so = fp->f_data;
@@ -257,7 +271,7 @@ listen(td, uap)
 	int error;
 
 	AUDIT_ARG_FD(uap->s);
-	error = getsock(td->td_proc->p_fd, uap->s, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, uap->s, CAP_LISTEN, &fp, NULL);
 	if (error == 0) {
 		so = fp->f_data;
 #ifdef MAC
@@ -347,7 +361,7 @@ kern_accept(struct thread *td, int s, struct sockaddr **name,
 
 	AUDIT_ARG_FD(s);
 	fdp = td->td_proc->p_fd;
-	error = getsock(fdp, s, &headfp, &fflag);
+	error = getsock_cap(fdp, s, CAP_ACCEPT, &headfp, &fflag);
 	if (error)
 		return (error);
 	head = headfp->f_data;
@@ -535,7 +549,7 @@ kern_connect(td, fd, sa)
 	int interrupted = 0;
 
 	AUDIT_ARG_FD(fd);
-	error = getsock(td->td_proc->p_fd, fd, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, fd, CAP_CONNECT, &fp, NULL);
 	if (error)
 		return (error);
 	so = fp->f_data;
@@ -744,12 +758,16 @@ kern_sendit(td, s, mp, flags, control, segflg)
 	struct socket *so;
 	int i;
 	int len, error;
+	cap_rights_t rights;
 #ifdef KTRACE
 	struct uio *ktruio = NULL;
 #endif
 
 	AUDIT_ARG_FD(s);
-	error = getsock(td->td_proc->p_fd, s, &fp, NULL);
+	rights = CAP_WRITE;
+	if (mp->msg_name != NULL)
+		rights |= CAP_CONNECT;
+	error = getsock_cap(td->td_proc->p_fd, s, rights, &fp, NULL);
 	if (error)
 		return (error);
 	so = (struct socket *)fp->f_data;
@@ -953,7 +971,7 @@ kern_recvit(td, s, mp, fromseg, controlp)
 		*controlp = NULL;
 
 	AUDIT_ARG_FD(s);
-	error = getsock(td->td_proc->p_fd, s, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, s, CAP_READ, &fp, NULL);
 	if (error)
 		return (error);
 	so = fp->f_data;
@@ -1267,7 +1285,8 @@ shutdown(td, uap)
 	int error;
 
 	AUDIT_ARG_FD(uap->s);
-	error = getsock(td->td_proc->p_fd, uap->s, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, uap->s, CAP_SHUTDOWN, &fp,
+	    NULL);
 	if (error == 0) {
 		so = fp->f_data;
 		error = soshutdown(so, uap->how);
@@ -1330,7 +1349,7 @@ kern_setsockopt(td, s, level, name, val, valseg, valsize)
 	}
 
 	AUDIT_ARG_FD(s);
-	error = getsock(td->td_proc->p_fd, s, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, s, CAP_SETSOCKOPT, &fp, NULL);
 	if (error == 0) {
 		so = fp->f_data;
 		error = sosetopt(so, &sopt);
@@ -1409,7 +1428,7 @@ kern_getsockopt(td, s, level, name, val, valseg, valsize)
 	}
 
 	AUDIT_ARG_FD(s);
-	error = getsock(td->td_proc->p_fd, s, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, s, CAP_GETSOCKOPT, &fp, NULL);
 	if (error == 0) {
 		so = fp->f_data;
 		error = sogetopt(so, &sopt);
@@ -1471,7 +1490,7 @@ kern_getsockname(struct thread *td, int fd, struct sockaddr **sa,
 		return (EINVAL);
 
 	AUDIT_ARG_FD(fd);
-	error = getsock(td->td_proc->p_fd, fd, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, fd, CAP_GETSOCKNAME, &fp, NULL);
 	if (error)
 		return (error);
 	so = fp->f_data;
@@ -1571,7 +1590,7 @@ kern_getpeername(struct thread *td, int fd, struct sockaddr **sa,
 		return (EINVAL);
 
 	AUDIT_ARG_FD(fd);
-	error = getsock(td->td_proc->p_fd, fd, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, fd, CAP_GETPEERNAME, &fp, NULL);
 	if (error)
 		return (error);
 	so = fp->f_data;
@@ -1827,7 +1846,7 @@ kern_sendfile(struct thread *td, struct sendfile_args *uap,
 	 * we send only the header/trailer and no payload data.
 	 */
 	AUDIT_ARG_FD(uap->fd);
-	if ((error = fgetvp_read(td, uap->fd, &vp)) != 0)
+	if ((error = fgetvp_read(td, uap->fd, CAP_READ, &vp)) != 0)
 		goto out;
 	vfslocked = VFS_LOCK_GIANT(vp->v_mount);
 	vn_lock(vp, LK_SHARED | LK_RETRY);
@@ -1865,8 +1884,8 @@ kern_sendfile(struct thread *td, struct sendfile_args *uap,
 	 * The socket must be a stream socket and connected.
 	 * Remember if it a blocking or non-blocking socket.
 	 */
-	if ((error = getsock(td->td_proc->p_fd, uap->s, &sock_fp,
-	    NULL)) != 0)
+	if ((error = getsock_cap(td->td_proc->p_fd, uap->s, CAP_WRITE,
+	    &sock_fp, NULL)) != 0)
 		goto out;
 	so = sock_fp->f_data;
 	if (so->so_type != SOCK_STREAM) {
@@ -2298,7 +2317,7 @@ sctp_peeloff(td, uap)
 
 	fdp = td->td_proc->p_fd;
 	AUDIT_ARG_FD(uap->sd);
-	error = fgetsock(td, uap->sd, &head, &fflag);
+	error = fgetsock(td, uap->sd, CAP_PEELOFF, &head, &fflag);
 	if (error)
 		goto done2;
 	error = sctp_can_peel_off(head, (sctp_assoc_t)uap->name);
@@ -2391,6 +2410,7 @@ sctp_generic_sendmsg (td, uap)
 #endif
 	struct uio auio;
 	struct iovec iov[1];
+	cap_rights_t rights;
 
 	if (uap->sinfo) {
 		error = copyin(uap->sinfo, &sinfo, sizeof (sinfo));
@@ -2398,16 +2418,19 @@ sctp_generic_sendmsg (td, uap)
 			return (error);
 		u_sinfo = &sinfo;
 	}
+
+	rights = CAP_WRITE;
 	if (uap->tolen) {
 		error = getsockaddr(&to, uap->to, uap->tolen);
 		if (error) {
 			to = NULL;
 			goto sctp_bad2;
 		}
+		rights |= CAP_CONNECT;
 	}
 
 	AUDIT_ARG_FD(uap->sd);
-	error = getsock(td->td_proc->p_fd, uap->sd, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, uap->sd, rights, &fp, NULL);
 	if (error)
 		goto sctp_bad;
 #ifdef KTRACE
@@ -2494,6 +2517,7 @@ sctp_generic_sendmsg_iov(td, uap)
 #endif
 	struct uio auio;
 	struct iovec *iov, *tiov;
+	cap_rights_t rights;
 
 	if (uap->sinfo) {
 		error = copyin(uap->sinfo, &sinfo, sizeof (sinfo));
@@ -2501,16 +2525,18 @@ sctp_generic_sendmsg_iov(td, uap)
 			return (error);
 		u_sinfo = &sinfo;
 	}
+	rights = CAP_WRITE;
 	if (uap->tolen) {
 		error = getsockaddr(&to, uap->to, uap->tolen);
 		if (error) {
 			to = NULL;
 			goto sctp_bad2;
 		}
+		rights |= CAP_CONNECT;
 	}
 
 	AUDIT_ARG_FD(uap->sd);
-	error = getsock(td->td_proc->p_fd, uap->sd, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, uap->sd, rights, &fp, NULL);
 	if (error)
 		goto sctp_bad1;
 
@@ -2618,7 +2644,7 @@ sctp_generic_recvmsg(td, uap)
 #endif
 
 	AUDIT_ARG_FD(uap->sd);
-	error = getsock(td->td_proc->p_fd, uap->sd, &fp, NULL);
+	error = getsock_cap(td->td_proc->p_fd, uap->sd, CAP_READ, &fp, NULL);
 	if (error) {
 		return (error);
 	}