ext4: don't allow any modifications to an immutable file

Don't allow any modifications to a file that's marked immutable, which
means that we have to flush all the writable pages to make the readonly
and we have to check the setattr/setflags parameters more closely.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

fs/ext4/ioctl.c

@@ -269,6 +269,29 @@ static int uuid_is_zero(__u8 u[16])
 }
 #endif
 
+/*
+ * If immutable is set and we are not clearing it, we're not allowed to change
+ * anything else in the inode.  Don't error out if we're only trying to set
+ * immutable on an immutable file.
+ */
+static int ext4_ioctl_check_immutable(struct inode *inode, __u32 new_projid,
+				      unsigned int flags)
+{
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	unsigned int oldflags = ei->i_flags;
+
+	if (!(oldflags & EXT4_IMMUTABLE_FL) || !(flags & EXT4_IMMUTABLE_FL))
+		return 0;
+
+	if ((oldflags & ~EXT4_IMMUTABLE_FL) != (flags & ~EXT4_IMMUTABLE_FL))
+		return -EPERM;
+	if (ext4_has_feature_project(inode->i_sb) &&
+	    __kprojid_val(ei->i_projid) != new_projid)
+		return -EPERM;
+
+	return 0;
+}
+
 static int ext4_ioctl_setflags(struct inode *inode,
 			       unsigned int flags)
 {
@@ -340,6 +363,20 @@ static int ext4_ioctl_setflags(struct inode *inode,
 		}
 	}
 
+	/*
+	 * Wait for all pending directio and then flush all the dirty pages
+	 * for this file.  The flush marks all the pages readonly, so any
+	 * subsequent attempt to write to the file (particularly mmap pages)
+	 * will come through the filesystem and fail.
+	 */
+	if (S_ISREG(inode->i_mode) && !IS_IMMUTABLE(inode) &&
+	    (flags & EXT4_IMMUTABLE_FL)) {
+		inode_dio_wait(inode);
+		err = filemap_write_and_wait(inode->i_mapping);
+		if (err)
+			goto flags_out;
+	}
+
 	handle = ext4_journal_start(inode, EXT4_HT_INODE, 1);
 	if (IS_ERR(handle)) {
 		err = PTR_ERR(handle);
@@ -769,6 +806,10 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			return err;
 
 		inode_lock(inode);
+		err = ext4_ioctl_check_immutable(inode,
+				from_kprojid(&init_user_ns, ei->i_projid),
+				flags);
+		if (!err)
 			err = ext4_ioctl_setflags(inode, flags);
 		inode_unlock(inode);
 		mnt_drop_write_file(filp);
@@ -1139,6 +1180,9 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			goto out;
 		flags = (ei->i_flags & ~EXT4_FL_XFLAG_VISIBLE) |
 			 (flags & EXT4_FL_XFLAG_VISIBLE);
+		err = ext4_ioctl_check_immutable(inode, fa.fsx_projid, flags);
+		if (err)
+			goto out;
 		err = ext4_ioctl_setflags(inode, flags);
 		if (err)
 			goto out;