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. Thanks, Roman.