Messages in this thread |  | | Date | Thu, 2 Apr 2020 16:14:04 +0000 | From | Luis Chamberlain <> | Subject | Re: [RFC 2/3] blktrace: fix debugfs use after free |
| |
On Wed, Apr 01, 2020 at 08:57:42PM -0500, Eric Sandeen wrote: > On 4/1/20 7:00 PM, Luis Chamberlain wrote: > > On commit 6ac93117ab00 ("blktrace: use existing disk debugfs directory") > > Omar fixed the original blktrace code for multiqueue use. 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: > > Weird, I swear I tested that and didn't hit it, but ...
The real issue was also the dangling block device, a loop device proves easy to test that. I'll note that another way to test this as well would be to have a virtual machine with a block devices that goes in and out via whatever virsh shenanigans to make a block device appear / disappear.
> > This issue can be reproduced with break-blktrace [2] using: > > > > break-blktrace -c 10 -d > > + -s, right?
Yeap, sorry about that.
> > This patch fixes this issue. Note that there is also another > > respective UAF but from the ioctl path [3], this should also fix > > that issue. > > > > This patch then also contends the severity of CVE-2019-19770 as > > this issue is only possible using root to shoot yourself in the > > foot by also misuing blktrace. > > > > [0] https://bugzilla.kernel.org/show_bug.cgi?id=205713 > > [1] https://nvd.nist.gov/vuln/detail/CVE-2019-19770 > > [2] https://github.com/mcgrof/break-blktrace > > I verified that this does reproduce the exact same KASAN splat on > kernel 4.19.83 as reported in the original bug, thanks!
I just codified what Nicolai suspected, we should thank him :)
Luis
|  |