Messages in this thread | | | Date | Tue, 10 Apr 2018 08:35:25 +0200 | From | Oleksandr Natalenko <> | Subject | Re: usercopy whitelist woe in scsi_sense_cache |
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Hi.
09.04.2018 22:30, Kees Cook wrote: >> echo 1 | tee /sys/block/sd*/queue/nr_requests > > I can't get this below "4".
Oops, yeah. It cannot be less than BLKDEV_MIN_RQ (which is 4), so it is enforced explicitly in queue_requests_store(). It is the same for me.
>> echo 1 | tee /sys/block/sd*/device/queue_depth > > I've got this now too. > Ah! dm-crypt too. I'll see if I can get that added easily to my tests. > And XFS! You love your corner cases. ;)
Yeah, so far this wonderful configuration has allowed me to uncover a bunch of bugs, and see, we are not done yet ;).
> Two other questions, since you can reproduce this easily: > - does it reproduce _without_ hardened usercopy? (I would assume yes, > but you'd just not get any warning until the hangs started.) If it > does reproduce without hardened usercopy, then a new bisect run could > narrow the search even more.
Looks like it cannot be disabled via kernel cmdline, so I have to re-compile the kernel, right? I can certainly do that anyway.
> - does it reproduce with Linus's current tree?
Will try this too.
> What would imply missing locking, yes? Yikes. But I'd expect > use-after-free or something, or bad data, not having the pointer slip > forward?
I still think this has something to do with blk-mq re-queuing capability and how BFQ implements it, because there are no sings of issue popping up with Kyber so far.
> Quick update: I added dm-crypt (with XFS on top) and it hung my system > almost immediately. I got no warnings at all, though.
Did your system hang on smartctl hammering too? Have you got some stack traces to compare with mine ones?
Regards, Oleksandr
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