ceph: add additional offset check in ceph_write_iter()

If the offset is larger or equal to both real file size and
max file size, then return -EFBIG.
Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/file.c

@@ -1384,12 +1384,12 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	struct ceph_file_info *fi = file->private_data;
 	struct inode *inode = file_inode(file);
 	struct ceph_inode_info *ci = ceph_inode(inode);
-	struct ceph_osd_client *osdc =
-		&ceph_sb_to_client(inode->i_sb)->client->osdc;
+	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
 	struct ceph_cap_flush *prealloc_cf;
 	ssize_t count, written = 0;
 	int err, want, got;
 	loff_t pos;
+	loff_t limit = max(i_size_read(inode), fsc->max_file_size);
 
 	if (ceph_snap(inode) != CEPH_NOSNAP)
 		return -EROFS;
@@ -1415,6 +1415,13 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		goto out;
 
 	pos = iocb->ki_pos;
+	if (unlikely(pos >= limit)) {
+		err = -EFBIG;
+		goto out;
+	} else {
+		iov_iter_truncate(from, limit - pos);
+	}
+
 	count = iov_iter_count(from);
 	if (ceph_quota_is_max_bytes_exceeded(inode, pos + count)) {
 		err = -EDQUOT;
@@ -1436,7 +1443,7 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	}
 
 	/* FIXME: not complete since it doesn't account for being at quota */
-	if (ceph_osdmap_flag(osdc, CEPH_OSDMAP_FULL)) {
+	if (ceph_osdmap_flag(&fsc->client->osdc, CEPH_OSDMAP_FULL)) {
 		err = -ENOSPC;
 		goto out;
 	}
@@ -1526,7 +1533,7 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	}
 
 	if (written >= 0) {
-		if (ceph_osdmap_flag(osdc, CEPH_OSDMAP_NEARFULL))
+		if (ceph_osdmap_flag(&fsc->client->osdc, CEPH_OSDMAP_NEARFULL))
 			iocb->ki_flags |= IOCB_DSYNC;
 		written = generic_write_sync(iocb, written);
 	}