NULL deref in integrity_inode_get

Sat Mar 20 07:13:14 UTC 2021

On Fri, Mar 19, 2021 at 9:22 PM Mimi Zohar <zohar at linux.ibm.com> wrote:
>
> On Thu, 2021-03-18 at 07:53 +0100, Dmitry Vyukov wrote:
> > On Thu, Mar 18, 2021 at 3:18 AM Mimi Zohar <zohar at linux.ibm.com> wrote:
> > >
> > > Hi Dmitry,
> > >
> > > On Mon, 2021-03-15 at 14:07 +0100, Dmitry Vyukov wrote:
> > > > On Mon, Mar 15, 2021 at 1:41 PM Mimi Zohar <zohar at linux.ibm.com> wrote:
> > > > >
> > > > > On Mon, 2021-03-15 at 11:58 +0100, Dmitry Vyukov wrote:
> > > > > > Hi,
> > > > > >
> > > > > > I am trying to boot 5.12-rc3 with this config:
> > > > > > https://github.com/google/syzkaller/blob/cc1cff8f1e1a585894796d6eae8c51eef98037e6/dashboard/config/linux/upstream-smack-kasan.config
> > > > > >
> > > > > > in qemu:
> > > > > > qemu-system-x86_64       -enable-kvm     -machine q35,nvdimm -cpu
> > > > > > max,migratable=off -smp 4       -m 4G,slots=4,maxmem=16G        -hda
> > > > > > wheezy.img      -kernel arch/x86/boot/bzImage   -nographic -vga std
> > > > > >  -soundhw all     -usb -usbdevice tablet  -bt hci -bt device:keyboard
> > > > > >    -net user,host=10.0.2.10,hostfwd=tcp::10022-:22 -net
> > > > > > nic,model=virtio-net-pci   -object
> > > > > > memory-backend-file,id=pmem1,share=off,mem-path=/dev/zero,size=64M
> > > > > >   -device nvdimm,id=nvdimm1,memdev=pmem1  -append "console=ttyS0
> > > > > > root=/dev/sda earlyprintk=serial rodata=n oops=panic panic_on_warn=1
> > > > > > panic=86400 lsm=smack numa=fake=2 nopcid dummy_hcd.num=8"   -pidfile
> > > > > > vm_pid -m 2G -cpu host
> > > > > >
> > > > > > But it crashes on NULL deref in integrity_inode_get during boot:
> > > > > >
> > > > > > Run /sbin/init as init process
> > > > > > BUG: kernel NULL pointer dereference, address: 000000000000001c
> > > > > > #PF: supervisor read access in kernel mode
> > > > > > #PF: error_code(0x0000) - not-present page
> > > > > > PGD 0 P4D 0
> > > > > > Oops: 0000 [#1] PREEMPT SMP KASAN
> > > > > > CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.12.0-rc2+ #97
> > > > > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
> > > > > > rel-1.13.0-44-g88ab0c15525c-prebuilt.qemu.org 04/01/2014
> > > > > > RIP: 0010:kmem_cache_alloc+0x2b/0x370 mm/slub.c:2920
> > > > > > Code: 57 41 56 41 55 41 54 41 89 f4 55 48 89 fd 53 48 83 ec 10 44 8b
> > > > > > 3d d9 1f 90 0b 65 48 8b 04 25 28 00 00 00 48 89 44 24 08 31 c0 <8b> 5f
> > > > > > 1c 4cf
> > > > > > RSP: 0000:ffffc9000032f9d8 EFLAGS: 00010246
> > > > > > RAX: 0000000000000000 RBX: ffff888017fc4f00 RCX: 0000000000000000
> > > > > > RDX: ffff888040220000 RSI: 0000000000000c40 RDI: 0000000000000000
> > > > > > RBP: 0000000000000000 R08: 0000000000000000 R09: ffff888019263627
> > > > > > R10: ffffffff83937cd1 R11: 0000000000000000 R12: 0000000000000c40
> > > > > > R13: ffff888019263538 R14: 0000000000000000 R15: 0000000000ffffff
> > > > > > FS:  0000000000000000(0000) GS:ffff88802d180000(0000) knlGS:0000000000000000
> > > > > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > > > CR2: 000000000000001c CR3: 000000000b48e000 CR4: 0000000000750ee0
> > > > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > > > > PKRU: 55555554
> > > > > > Call Trace:
> > > > > >  integrity_inode_get+0x47/0x260 security/integrity/iint.c:105
> > > > > >  process_measurement+0x33d/0x17e0 security/integrity/ima/ima_main.c:237
> > > > > >  ima_bprm_check+0xde/0x210 security/integrity/ima/ima_main.c:474
> > > > > >  security_bprm_check+0x7d/0xa0 security/security.c:845
> > > > > >  search_binary_handler fs/exec.c:1708 [inline]
> > > > > >  exec_binprm fs/exec.c:1761 [inline]
> > > > > >  bprm_execve fs/exec.c:1830 [inline]
> > > > > >  bprm_execve+0x764/0x19a0 fs/exec.c:1792
> > > > > >  kernel_execve+0x370/0x460 fs/exec.c:1973
> > > > > >  try_to_run_init_process+0x14/0x4e init/main.c:1366
> > > > > >  kernel_init+0x11d/0x1b8 init/main.c:1477
> > > > > >  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> > > > > > Modules linked in:
> > > > > > CR2: 000000000000001c
> > > > > > ---[ end trace 22d601a500de7d79 ]---
> > > > >
> > > > > It looks like integrity_inode_get() fails to alloc memory.   Only on
> > > > > failure to verify the integrity of a file would an error be returned.
> > > > > I think that is what you would want to happen.  Without an "appraise"
> > > > > policy, this shouldn't happen.
> > > >
> > > > It happens at the very boot. I think the cache is NULL.
> > >
> > > An IMA policy had to have been loaded in order for
> > > integrity_inode_get() to have been called.   If this is happening on
> > > boot, it's too early for a custom policy to have been loaded by
> > > userspace, but I don't see the builtin policy defined on the boot
> > > command line either.
> > >
> > > Any additional information would be much appreciated.
> >
> > Hi Mimi,
> >
> > I provided kernel config and qemu command line. What other information
> > are you looking for? Can you reproduce it on your side?
>
> Yes, finally I was able to reproduce the NULL deref.  I just posted two
> patches as an RFC.  As described in the 2/2 patch description, it's
> unclear why the iint_cache would not be initialized, yet an IMA policy
> is loaded.  If the kmem_cache_alloc() for the iint_cache failed, it
> would have panic'ed.  Perhaps you have some insights as to how this
> might happen.
>
> Once reviewed/tested, I'll re-post a proper patch (fixing the patch
> author).

Hi Mimi,

I know almost nothing about the security subsystem in general and
integrity subsystem in particular. I think you are much better
equipped to answer these questions.
You said you can reproduce it, doesn't it allow you to understand what
happens? E.g. by adding maybe some additional printf's to trace
execution of some key initialization points.