Index: ffs_vfsops.c
===================================================================
RCS file: /home/ncvs/src/sys/ufs/ffs/ffs_vfsops.c,v
retrieving revision 1.234
diff -u -r1.234 ffs_vfsops.c
--- ffs_vfsops.c	4 Jul 2004 08:52:35 -0000	1.234
+++ ffs_vfsops.c	6 Jul 2004 05:06:15 -0000
@@ -51,6 +51,7 @@
 #include <sys/disk.h>
 #include <sys/malloc.h>
 #include <sys/mutex.h>
+#include <sys/stat.h>
 
 #include <ufs/ufs/extattr.h>
 #include <ufs/ufs/quota.h>
@@ -148,6 +149,7 @@
 	struct fs *fs;
 	int error, flags;
 	mode_t accessmode;
+	struct vattr va;
 
 	if (uma_inode == NULL) {
 		uma_inode = uma_zcreate("FFS inode",
@@ -189,6 +191,32 @@
 		ump = VFSTOUFS(mp);
 		fs = ump->um_fs;
 		devvp = ump->um_devvp;
+		/*
+		 * Disallow write mounting on a UFS file system mounted from
+		 * a UFS snapshot.
+		 *
+		 * XXX: This is almost certainly not the right place to do
+		 * this check -- it's here because we ignore the VOP_ACCESS()
+		 * for the root user.
+		 *
+		 * XXX: Note that this code is duplicated between the update
+		 * and new mount paths, so remember to modify both if you
+		 * change either.
+		 */
+		if ((mp->mnt_flag & MNT_RDONLY) == 0) {
+			vn_lock(devvp, LK_EXCLUSIVE | LK_RETRY, td);
+			error = VOP_GETATTR(devvp, &va, td->td_ucred, td);
+			if (error != 0) {
+				vput(devvp);
+				return (error);
+			}
+			if ((va.va_flags & SF_SNAPSHOT) != 0) {
+				vput(devvp);
+				return (EACCES);
+			}
+			VOP_UNLOCK(devvp, 0, td);
+		}
+
 		if (fs->fs_ronly == 0 && (mp->mnt_flag & MNT_RDONLY)) {
 			if ((error = vn_start_write(NULL, &mp, V_WAIT)) != 0)
 				return (error);
@@ -322,6 +350,30 @@
 	}
 
 	/*
+	 * Disallow write mounting on a UFS file system mounted from a UFS
+	 * snapshot.
+	 *
+	 * XXX: This is almost certainly not the right place to do this check
+	 * -- it's here because we ignore the VOP_ACCESS() for the root user.
+	 *
+	 * XXX: Note that this code is duplicated between the update and new
+	 * mount paths, so remember to modify both if you change either.
+	 */
+	if ((mp->mnt_flag & MNT_RDONLY) == 0) {
+		vn_lock(devvp, LK_EXCLUSIVE | LK_RETRY, td);
+		error = VOP_GETATTR(devvp, &va, td->td_ucred, td);
+		if (error != 0) {
+			vput(devvp);
+			return (error);
+		}
+		if ((va.va_flags & SF_SNAPSHOT) != 0) {
+			vput(devvp);
+			return (EACCES);
+		}
+		VOP_UNLOCK(devvp, 0, td);
+	}
+
+	/*
 	 * If mount by non-root, then verify that user has necessary
 	 * permissions on the device.
 	 */