ceph: check negative offsets in ceph_llseek()

When a user requests SEEK_HOLE or SEEK_DATA with a negative offset
ceph_llseek should return -ENXIO.  Currently -EINVAL is being returned for
SEEK_DATA and 0 for SEEK_HOLE.
Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/file.c

@@ -1481,13 +1481,13 @@ static loff_t ceph_llseek(struct file *file, loff_t offset, int whence)
 		offset += file->f_pos;
 		break;
 	case SEEK_DATA:
-		if (offset >= i_size) {
+		if (offset < 0 || offset >= i_size) {
 			ret = -ENXIO;
 			goto out;
 		}
 		break;
 	case SEEK_HOLE:
-		if (offset >= i_size) {
+		if (offset < 0 || offset >= i_size) {
 			ret = -ENXIO;
 			goto out;
 		}