NULL deref in integrity_inode_get

[Mimi Zohar]

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).

thanks,

Mimi