Re: NULL deref in integrity_inode_get

[Mimi Zohar]

Hi Dmitry,

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.

Mimi