nilfs2: reject invalid file types when reading inodes

To prevent inodes with invalid file types from tripping through the vfs
and causing malfunctions or assertion failures, add a missing sanity check
when reading an inode from a block device.  If the file type is not valid,
treat it as a filesystem error.

Link: https://lkml.kernel.org/r/20250710134952.29862-1-konishi.ryusuke@gmail.com
Fixes: 05fe58f ("nilfs2: inode operations")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+895c23f6917da440ed0d@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=895c23f6917da440ed0d
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: konis

fs/nilfs2/inode.c

@@ -472,11 +472,18 @@ static int __nilfs_read_inode(struct super_block *sb,
 		inode->i_op = &nilfs_symlink_inode_operations;
 		inode_nohighmem(inode);
 		inode->i_mapping->a_ops = &nilfs_aops;
-	} else {
+	} else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
+		   S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
 		inode->i_op = &nilfs_special_inode_operations;
 		init_special_inode(
 			inode, inode->i_mode,
 			huge_decode_dev(le64_to_cpu(raw_inode->i_device_code)));
+	} else {
+		nilfs_error(sb,
+			    "invalid file type bits in mode 0%o for inode %lu",
+			    inode->i_mode, ino);
+		err = -EIO;
+		goto failed_unmap;
 	}
 	nilfs_ifile_unmap_inode(raw_inode);
 	brelse(bh);