Messages in this thread | | | Subject | Re: [PATCH 2/5] blktrace: fix debugfs use after free | From | Eric Sandeen <> | Date | Wed, 15 Apr 2020 20:02:04 -0500 |
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On 4/15/20 7:56 PM, Luis Chamberlain wrote: > On Wed, Apr 15, 2020 at 12:38:26PM -0500, Eric Sandeen wrote: >> On 4/13/20 11:18 PM, Luis Chamberlain wrote: >>> On commit 6ac93117ab00 ("blktrace: use existing disk debugfs directory") >>> merged on v4.12 Omar fixed the original blktrace code for request-based >>> drivers (multiqueue). This however left in place a possible crash, if you >>> happen to abuse blktrace in a way it was not intended. >>> >>> Namely, if you loop adding a device, setup the blktrace with BLKTRACESETUP, >>> forget to BLKTRACETEARDOWN, and then just remove the device you end up >>> with a panic: >> >> I think this patch makes this all cleaner anyway, but - without the apparent >> loop bug mentioned by Bart which allows removal of the loop device while blktrace >> is active (if I read that right), can this still happen? > > I have not tested that, but some modifications of the break-blktrace > program could enable us to test that
FWIW, I modified it to modprobe & rmmod scsi_debug instead of the loop ioctls, and the module can't be unloaded after the blktrace is started since it's busy.
Not sure that's equivalent tho.
> however I don't think the race > would be possible after patch 3/5 "blktrace: refcount the request_queue > during ioctl" is merged, as removal then a pending blktrace would > refcount the request_queue and the removal would have to wait until > the refcount is decremeneted, until after the blktrace ioctl.
I'm out of my depth in the block layer, not sure who's supposed to take refs on what. ;)
-Eric
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