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, 74 insertions, 32 deletions

diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index b48c6e796958..3a7ca062faad 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -37,6 +37,7 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include "opt_capsicum.h"
 #include "opt_compat.h"
 #include "opt_kdtrace.h"
 #include "opt_ktrace.h"
@@ -45,6 +46,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/systm.h>
 #include <sys/bio.h>
 #include <sys/buf.h>
+#include <sys/capability.h>
 #include <sys/disk.h>
 #include <sys/sysent.h>
 #include <sys/malloc.h>
@@ -373,7 +375,7 @@ kern_fstatfs(struct thread *td, int fd, struct statfs *buf)
 	int error;
 
 	AUDIT_ARG_FD(fd);
-	error = getvnode(td->td_proc->p_fd, fd, &fp);
+	error = getvnode(td->td_proc->p_fd, fd, CAP_FSTATFS, &fp);
 	if (error)
 		return (error);
 	vp = fp->f_vnode;
@@ -746,7 +748,7 @@ fchdir(td, uap)
 	int error;
 
 	AUDIT_ARG_FD(uap->fd);
-	if ((error = getvnode(fdp, uap->fd, &fp)) != 0)
+	if ((error = getvnode(fdp, uap->fd, CAP_FCHDIR, &fp)) != 0)
 		return (error);
 	vp = fp->f_vnode;
 	VREF(vp);
@@ -1049,7 +1051,7 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
 	struct vnode *vp;
 	int cmode;
 	struct file *nfp;
-	int type, indx, error;
+	int type, indx = -1, error;
 	struct flock lf;
 	struct nameidata nd;
 	int vfslocked;
@@ -1069,10 +1071,13 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
 	else
 		flags = FFLAGS(flags);
 
-	error = falloc(td, &nfp, &indx, flags);
+	/*
+	 * allocate the file descriptor, but don't install a descriptor yet
+	 */
+	error = falloc_noinstall(td, &nfp);
 	if (error)
 		return (error);
-	/* An extra reference on `nfp' has been held for us by falloc(). */
+	/* An extra reference on `nfp' has been held for us by falloc_noinstall(). */
 	fp = nfp;
 	/* Set the flags early so the finit in devfs can pick them up. */
 	fp->f_flag = flags & FMASK;
@@ -1099,12 +1104,13 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
 		 * if it succeeds.
 		 */
 		if ((error == ENODEV || error == ENXIO) &&
-		    td->td_dupfd >= 0 &&		/* XXX from fdopen */
-		    (error =
-			dupfdopen(td, fdp, indx, td->td_dupfd, flags, error)) == 0) {
-			td->td_retval[0] = indx;
-			fdrop(fp, td);
-			return (0);
+		    (td->td_dupfd >= 0)) {
+			/* XXX from fdopen */
+			if ((error = finstall(td, fp, &indx, flags)) != 0)
+				goto bad_unlocked;
+			if ((error = dupfdopen(td, fdp, indx, td->td_dupfd,
+			    flags, error)) == 0)
+				goto success;
 		}
 		/*
 		 * Clean up the descriptor, but only if another thread hadn't
@@ -1161,6 +1167,14 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
 			goto bad;
 	}
 	VFS_UNLOCK_GIANT(vfslocked);
+success:
+	/*
+	 * If we haven't already installed the FD (for dupfdopen), do so now.
+	 */
+	if (indx == -1)
+		if ((error = finstall(td, fp, &indx, flags)) != 0)
+			goto bad_unlocked;
+
 	/*
 	 * Release our private reference, leaving the one associated with
 	 * the descriptor table intact.
@@ -1170,8 +1184,10 @@ kern_openat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
 	return (0);
 bad:
 	VFS_UNLOCK_GIANT(vfslocked);
+bad_unlocked:
 	fdclose(fdp, fp, indx, td);
 	fdrop(fp, td);
+	td->td_retval[0] = -1;
 	return (error);
 }
 
@@ -1918,7 +1934,7 @@ lseek(td, uap)
 	int vfslocked;
 
 	AUDIT_ARG_FD(uap->fd);
-	if ((error = fget(td, uap->fd, &fp)) != 0)
+	if ((error = fget(td, uap->fd, CAP_SEEK, &fp)) != 0)
 		return (error);
 	if (!(fp->f_ops->fo_flags & DFLAG_SEEKABLE)) {
 		fdrop(fp, td);
@@ -2775,7 +2791,8 @@ fchflags(td, uap)
 
 	AUDIT_ARG_FD(uap->fd);
 	AUDIT_ARG_FFLAGS(uap->flags);
-	if ((error = getvnode(td->td_proc->p_fd, uap->fd, &fp)) != 0)
+	if ((error = getvnode(td->td_proc->p_fd, uap->fd, CAP_FCHFLAGS,
+	    &fp)) != 0)
 		return (error);
 	vfslocked = VFS_LOCK_GIANT(fp->f_vnode->v_mount);
 #ifdef AUDIT
@@ -2936,7 +2953,8 @@ fchmod(td, uap)
 
 	AUDIT_ARG_FD(uap->fd);
 	AUDIT_ARG_MODE(uap->mode);
-	if ((error = getvnode(td->td_proc->p_fd, uap->fd, &fp)) != 0)
+	if ((error = getvnode(td->td_proc->p_fd, uap->fd, CAP_FCHMOD,
+	    &fp)) != 0)
 		return (error);
 	vfslocked = VFS_LOCK_GIANT(fp->f_vnode->v_mount);
 #ifdef AUDIT
@@ -3113,7 +3131,8 @@ fchown(td, uap)
 
 	AUDIT_ARG_FD(uap->fd);
 	AUDIT_ARG_OWNER(uap->uid, uap->gid);
-	if ((error = getvnode(td->td_proc->p_fd, uap->fd, &fp)) != 0)
+	if ((error = getvnode(td->td_proc->p_fd, uap->fd, CAP_FCHOWN, &fp))
+	    != 0)
 		return (error);
 	vfslocked = VFS_LOCK_GIANT(fp->f_vnode->v_mount);
 #ifdef AUDIT
@@ -3348,7 +3367,8 @@ kern_futimes(struct thread *td, int fd, struct timeval *tptr,
 	AUDIT_ARG_FD(fd);
 	if ((error = getutimes(tptr, tptrseg, ts)) != 0)
 		return (error);
-	if ((error = getvnode(td->td_proc->p_fd, fd, &fp)) != 0)
+	if ((error = getvnode(td->td_proc->p_fd, fd, CAP_FUTIMES, &fp))
+	    != 0)
 		return (error);
 	vfslocked = VFS_LOCK_GIANT(fp->f_vnode->v_mount);
 #ifdef AUDIT
@@ -3500,7 +3520,8 @@ fsync(td, uap)
 	int error, lock_flags;
 
 	AUDIT_ARG_FD(uap->fd);
-	if ((error = getvnode(td->td_proc->p_fd, uap->fd, &fp)) != 0)
+	if ((error = getvnode(td->td_proc->p_fd, uap->fd, CAP_FSYNC,
+	    &fp)) != 0)
 		return (error);
 	vp = fp->f_vnode;
 	vfslocked = VFS_LOCK_GIANT(vp->v_mount);
@@ -3925,7 +3946,8 @@ kern_ogetdirentries(struct thread *td, struct ogetdirentries_args *uap,
 	/* XXX arbitrary sanity limit on `count'. */
 	if (uap->count > 64 * 1024)
 		return (EINVAL);
-	if ((error = getvnode(td->td_proc->p_fd, uap->fd, &fp)) != 0)
+	if ((error = getvnode(td->td_proc->p_fd, uap->fd, CAP_READ,
+	    &fp)) != 0)
 		return (error);
 	if ((fp->f_flag & FREAD) == 0) {
 		fdrop(fp, td);
@@ -4085,7 +4107,8 @@ kern_getdirentries(struct thread *td, int fd, char *buf, u_int count,
 	AUDIT_ARG_FD(fd);
 	if (count > INT_MAX)
 		return (EINVAL);
-	if ((error = getvnode(td->td_proc->p_fd, fd, &fp)) != 0)
+	if ((error = getvnode(td->td_proc->p_fd, fd, CAP_READ | CAP_SEEK,
+	    &fp)) != 0)
 		return (error);
 	if ((fp->f_flag & FREAD) == 0) {
 		fdrop(fp, td);
@@ -4248,30 +4271,49 @@ out:
 }
 
 /*
- * Convert a user file descriptor to a kernel file entry.
- * A reference on the file entry is held upon returning.
+ * Convert a user file descriptor to a kernel file entry and check that, if it
+ * is a capability, the correct rights are present. A reference on the file
+ * entry is held upon returning.
  */
 int
-getvnode(fdp, fd, fpp)
-	struct filedesc *fdp;
-	int fd;
-	struct file **fpp;
+getvnode(struct filedesc *fdp, int fd, cap_rights_t rights,
+    struct file **fpp)
 {
-	int error;
 	struct file *fp;
+#ifdef CAPABILITIES
+	struct file *fp_fromcap;
+#endif
+	int error;
 
 	error = 0;
 	fp = NULL;
-	if (fdp == NULL || (fp = fget_unlocked(fdp, fd)) == NULL)
-		error = EBADF;
-	else if (fp->f_vnode == NULL) {
-		error = EINVAL;
+	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);
+		return (error);
+	}
+	if (fp != fp_fromcap) {
+		fhold(fp_fromcap);
+		fdrop(fp, curthread);
+		fp = fp_fromcap;
+	}
+#endif /* CAPABILITIES */
+	if (fp->f_vnode == NULL) {
 		fdrop(fp, curthread);
+		return (EINVAL);
 	}
 	*fpp = fp;
-	return (error);
+	return (0);
 }
 
+
 /*
  * Get an (NFS) file handle.
  */
@@ -4683,7 +4725,7 @@ kern_posix_fallocate(struct thread *td, int fd, off_t offset, off_t len)
 
 	fp = NULL;
 	vfslocked = 0;
-	error = fget(td, fd, &fp);
+	error = fget(td, fd, CAP_WRITE, &fp);
 	if (error != 0)
 		goto out;