KASAN: null-ptr-deref Read in kvm_vfio_set

KASAN: null-ptr-deref Read in kvm_vfio_set_attr
Status: upstream: reported syz repro on 2020/03/27 08:30
Reported-by: syzbot+c8f52ab16178cebd5f5c@syzkaller.appspotmail.com
First crash: 71d, last: 71d

Cause bisection: the bug happens on the oldest tested release
Crash: WARNING in sysfs_warn_dup (log)
Repro: syz .config

Sample crash report:

==================================================================
BUG: KASAN: null-ptr-deref in kvm_vfio_set_group arch/x86/kvm/../../../virt/kvm/vfio.c:235 [inline]
BUG: KASAN: null-ptr-deref in kvm_vfio_set_attr+0x7da/0xa30 arch/x86/kvm/../../../virt/kvm/vfio.c:337
Read of size 8 at addr 0000000000000000 by task syz-executor.2/9641

CPU: 0 PID: 9641 Comm: syz-executor.2 Not tainted 5.6.0-rc3-next-20200228-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 __kasan_report.cold+0x5/0x32 mm/kasan/report.c:510
 kasan_report+0xe/0x20 mm/kasan/common.c:618
 kvm_vfio_set_group arch/x86/kvm/../../../virt/kvm/vfio.c:235 [inline]
 kvm_vfio_set_attr+0x7da/0xa30 arch/x86/kvm/../../../virt/kvm/vfio.c:337
 </IRQ>
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 9641 Comm: syz-executor.2 Tainted: G    B             5.6.0-rc3-next-20200228-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 panic+0x2e3/0x75c kernel/panic.c:221
 end_report+0x43/0x49 mm/kasan/report.c:96
 __kasan_report.cold+0xd/0x32 mm/kasan/report.c:513
 kasan_report+0xe/0x20 mm/kasan/common.c:618
 kvm_vfio_set_group arch/x86/kvm/../../../virt/kvm/vfio.c:235 [inline]
 kvm_vfio_set_attr+0x7da/0xa30 arch/x86/kvm/../../../virt/kvm/vfio.c:337
 </IRQ>
Shutting down cpus with NMI
Kernel Offset: disabled
Rebooting in 86400 seconds..

Crashes (1):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	Maintainers
ci-upstream-linux-next-kasan-gce-root	2020/03/23 08:22	linux-next	770fbb32	78267cec	.config	log	report	syz		kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com