On Wed, Jan 24, 2018 at 11:49:26AM +0800, Ming Lei wrote: > 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. I agreed this is not a elegant fix but, as Ming suggested, might be the simplest. I could put more comments in the code about why the comparison makes sense. Thanks, Eryu > > > 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
