On Sat, May 19, 2018 at 09:26:36AM +0300, Roman Kagan wrote: > On Fri, May 18, 2018 at 03:31:38PM -0700, Andrew Morton wrote: > > On Fri, 18 May 2018 10:50:25 -0700 Matthew Wilcox <wi...@infradead.org> > > wrote: > > > > > If the radix tree underlying the IDR happens to be full and we attempt > > > to remove an id which is larger than any id in the IDR, we will call > > > __radix_tree_delete() with an uninitialised 'slot' pointer, at which > > > point anything could happen. This was easiest to hit with a single entry > > > at id 0 and attempting to remove a non-0 id, but it could have happened > > > with 64 entries and attempting to remove an id >= 64. > > > > > > Fixes: 0a835c4f090a ("Reimplement IDR and IDA using the radix tree") > > > Reported-by: syzbot+35666cba7f0a337e2...@syzkaller.appspotmail.com > > > Debugged-by: Roman Kagan <rka...@virtuozzo.com> > > > Signed-off-by: Matthew Wilcox <mawil...@microsoft.com> > > > > Neither of the changelogs I'm seeing attempt to describe the end-user > > impact of the bug. People like to know that so they can decide which > > kernel version(s) need patching, so please always remember it. > > That's my fault, Matthew may not have seen the original discussion among > the KVM folks. > > > Looknig at the sysbot report, the impact is at least "privileged user > > can trigger a WARN", but I assume there could be worse, > > Unfortunately it is worse: the syzcaller test boils down to opening > /dev/kvm, creating an eventfd, and calling a couple of KVM ioctls. None > of this requires superuser. And the result is dereferencing an > uninitialized pointer which is likely a crash. > > > as-yet-undiscovered impacts. So I'm thinking a cc:stable is needed, > > yes? > > Well the specific path caught by syzbot is via KVM_HYPERV_EVENTD ioctl > which is new in 4.17. But I guess there are other user-triggerable > paths, so cc:stable is probably justified.
We have around 250 calls to idr_remove() in the kernel today. Many of them pass an ID which is embedded in the object they're removing, so they're safe. Picking a few likely candidates: drivers/firewire/core-cdev.c looks unsafe; the ID comes from an ioctl. drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c is similar drivers/atm/nicstar.c could be taken down by a handcrafted packet