On Tue, Jan 23, 2018 at 02:32:06PM -0700, Jens Axboe wrote: > On 1/23/18 10:20 AM, Eryu Guan wrote: > > Attributes that only implement .seq_ops are read-only, any write to > > them should be rejected. But currently kernel would crash when > > writing to such debugfs entries, e.g. > > > > chmod +w /sys/kernel/debug/block/<dev>/requeue_list > > echo 0 > /sys/kernel/debug/block/<dev>/requeue_list > > chmod -w /sys/kernel/debug/block/<dev>/requeue_list > > > > Fix it by returning -EPERM in blk_mq_debugfs_write() when writing to > > such attributes. > > I don't particularly like the fix, since it's not really clear why > that comparison makes sense. Can't we just prevent anyone from It might be the simplest way to check if the attribute defines .seq_ops or not. If it is .seq_ops, it is wrong to interpret m->private as 'struct blk_mq_debugfs_attr *' because it actually points to 'struct request_queue *' or others, which depends on the specific attribute. So it works for avoiding the oops. > making the debugfs entries writable? Seems like a much more sane > approach. I guess fs should allow root user to do 'chmod +w' on files in proc, debugfs or sysfs. I just tried, it works on proc, debugfs and sysfs. Thanks, Ming
