apparmor: fix possible NULL pointer dereference

In the Linux kernel, the following vulnerability has been resolved:

apparmor: fix possible NULL pointer dereference

profile->parent->dents[AAFS_PROF_DIR] could be NULL only if its parent is made
from __create_missing_ancestors(..) and 'ent->old' is NULL in
aa_replace_profiles(..).
In that case, it must return an error code and the code, -ENOENT represents
its state that the path of its parent is not existed yet.

BUG: kernel NULL pointer dereference, address: 0000000000000030
PGD 0 P4D 0
PREEMPT SMP PTI
CPU: 4 PID: 3362 Comm: apparmor_parser Not tainted 6.8.0-24-generic #24
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
RIP: 0010:aafs_create.constprop.0+0x7f/0x130
Code: 4c 63 e0 48 83 c4 18 4c 89 e0 5b 41 5c 41 5d 41 5e 41 5f 5d 31 d2 31 c9 31 f6 31 ff 45 31 c0 45 31 c9 45 31 d2 c3 cc cc cc cc <4d> 8b 55 30 4d 8d ba a0 00 00 00 4c 89 55 c0 4c 89 ff e8 7a 6a ae
RSP: 0018:ffffc9000b2c7c98 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 00000000000041ed RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc9000b2c7cd8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff82baac10
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 00007be9f22cf740(0000) GS:ffff88817bc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000030 CR3: 0000000134b08000 CR4: 00000000000006f0
Call Trace:
<TASK>
? show_regs+0x6d/0x80
? __die+0x24/0x80
? page_fault_oops+0x99/0x1b0
? kernelmode_fixup_or_oops+0xb2/0x140
? __bad_area_nosemaphore+0x1a5/0x2c0
? find_vma+0x34/0x60
? bad_area_nosemaphore+0x16/0x30
? do_user_addr_fault+0x2a2/0x6b0
? exc_page_fault+0x83/0x1b0
? asm_exc_page_fault+0x27/0x30
? aafs_create.constprop.0+0x7f/0x130
? aafs_create.constprop.0+0x51/0x130
__aafs_profile_mkdir+0x3d6/0x480
aa_replace_profiles+0x83f/0x1270
policy_update+0xe3/0x180
profile_load+0xbc/0x150
? rw_verify_area+0x47/0x140
vfs_write+0x100/0x480
? __x64_sys_openat+0x55/0xa0
? syscall_exit_to_user_mode+0x86/0x260
ksys_write+0x73/0x100
__x64_sys_write+0x19/0x30
x64_sys_call+0x7e/0x25c0
do_syscall_64+0x7f/0x180
entry_SYSCALL_64_after_hwframe+0x78/0x80
RIP: 0033:0x7be9f211c574
Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d d5 ea 0e 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 55 48 89 e5 48 83 ec 20 48 89
RSP: 002b:00007ffd26f2b8c8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00005d504415e200 RCX: 00007be9f211c574
RDX: 0000000000001fc1 RSI: 00005d504418bc80 RDI: 0000000000000004
RBP: 0000000000001fc1 R08: 0000000000001fc1 R09: 0000000080000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00005d504418bc80
R13: 0000000000000004 R14: 00007ffd26f2b9b0 R15: 00007ffd26f2ba30
</TASK>
Modules linked in: snd_seq_dummy snd_hrtimer qrtr snd_hda_codec_generic snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec snd_hda_core snd_hwdep snd_pcm snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device i2c_i801 snd_timer i2c_smbus qxl snd soundcore drm_ttm_helper lpc_ich ttm joydev input_leds serio_raw mac_hid binfmt_misc msr parport_pc ppdev lp parport efi_pstore nfnetlink dmi_sysfs qemu_fw_cfg ip_tables x_tables autofs4 hid_generic usbhid hid ahci libahci psmouse virtio_rng xhci_pci xhci_pci_renesas
CR2: 0000000000000030
---[ end trace 0000000000000000 ]---
RIP: 0010:aafs_create.constprop.0+0x7f/0x130
Code: 4c 63 e0 48 83 c4 18 4c 89 e0 5b 41 5c 41 5d 41 5e 41 5f 5d 31 d2 31 c9 31 f6 31 ff 45 31 c0 45 31 c9 45 31 d2 c3 cc cc cc cc <4d> 8b 55 30 4d 8d ba a0 00 00 00 4c 89 55 c0 4c 89 ff e8 7a 6a ae
RSP: 0018:ffffc9000b2c7c98 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 00000000000041ed RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc9000b2c7cd8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000
---truncated---