CVE-2023-3772: Linux kernel: xfrm_update_ae_params NULL pointer dereference

["Lin Ma" <linma () zju edu cn>]

Hello there, we found a NPD bug in Linux kernel XFRM submodule.

[require privilege]: CAP_NET_ADMIN (namespace)

[effects]: local DoS

[crash stack]:
[   47.933119] BUG: kernel NULL pointer dereference, address: 0000000000000000
[   47.933119] #PF: supervisor write access in kernel mode
[   47.933119] #PF: error_code(0x0002) - not-present page
[   47.933119] PGD 8253067 P4D 8253067 PUD 8e0e067 PMD 0
[   47.933119] Oops: 0002 [#1] PREEMPT SMP KASAN NOPTI
[   47.933119] CPU: 0 PID: 98 Comm: poc.npd Not tainted 6.4.0-rc7-00072-gdad9774deaf1 #8
[   47.933119] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.o4
[   47.933119] RIP: 0010:memcpy_orig+0xad/0x140
[   47.933119] Code: e8 4c 89 5f e0 48 8d 7f e0 73 d2 83 c2 20 48 29 d6 48 29 d7 83 fa 10 72 34 4c 8b 06 4c 8b 4e 08 c
[   47.933119] RSP: 0018:ffff888008f57658 EFLAGS: 00000202
[   47.933119] RAX: 0000000000000000 RBX: ffff888008bd0000 RCX: ffffffff8238e571
[   47.933119] RDX: 0000000000000018 RSI: ffff888007f64844 RDI: 0000000000000000
[   47.933119] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   47.933119] R10: 0000000000000000 R11: 0000000000000000 R12: ffff888008f57818
[   47.933119] R13: ffff888007f64aa4 R14: 0000000000000000 R15: 0000000000000000
[   47.933119] FS:  00000000014013c0(0000) GS:ffff88806d600000(0000) knlGS:0000000000000000
[   47.933119] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   47.933119] CR2: 0000000000000000 CR3: 00000000054d8000 CR4: 00000000000006f0
[   47.933119] Call Trace:
[   47.933119]  <TASK>
[   47.933119]  ? __die+0x1f/0x70
[   47.933119]  ? page_fault_oops+0x1e8/0x500
[   47.933119]  ? __pfx_is_prefetch.constprop.0+0x10/0x10
[   47.933119]  ? __pfx_page_fault_oops+0x10/0x10
[   47.933119]  ? _raw_spin_unlock_irqrestore+0x11/0x40
[   47.933119]  ? fixup_exception+0x36/0x460
[   47.933119]  ? _raw_spin_unlock_irqrestore+0x11/0x40
[   47.933119]  ? exc_page_fault+0x5e/0xc0
[   47.933119]  ? asm_exc_page_fault+0x26/0x30
[   47.933119]  ? xfrm_update_ae_params+0xd1/0x260
[   47.933119]  ? memcpy_orig+0xad/0x140
[   47.933119]  ? __pfx__raw_spin_lock_bh+0x10/0x10
[   47.933119]  xfrm_update_ae_params+0xe7/0x260
[   47.933119]  xfrm_new_ae+0x298/0x4e0
[   47.933119]  ? __pfx_xfrm_new_ae+0x10/0x10
[   47.933119]  xfrm_user_rcv_msg+0x25a/0x410
[   47.933119]  ? __pfx_xfrm_user_rcv_msg+0x10/0x10
[   47.933119]  ? __alloc_skb+0xcf/0x210
[   47.933119]  ? stack_trace_save+0x90/0xd0
[   47.933119]  ? filter_irq_stacks+0x1c/0x70
[   47.933119]  ? __stack_depot_save+0x39/0x4e0
[   47.933119]  ? __kasan_slab_free+0x10a/0x190
[   47.933119]  ? kmem_cache_free+0x9c/0x340
[   47.933119]  ? netlink_recvmsg+0x23c/0x660
[   47.933119]  ? sock_recvmsg+0xeb/0xf0
[   47.933119]  ? __sys_recvfrom+0x13c/0x1f0
[   47.933119]  ? __x64_sys_recvfrom+0x71/0x90
[   47.933119]  ? do_syscall_64+0x3f/0x90
[   47.933119]  ? entry_SYSCALL_64_after_hwframe+0x72/0xdc
[   47.933119]  ? copyout+0x3e/0x50
[   47.933119]  netlink_rcv_skb+0xd6/0x210
[   47.933119]  ? __pfx_xfrm_user_rcv_msg+0x10/0x10
[   47.933119]  ? __pfx_netlink_rcv_skb+0x10/0x10
[   47.933119]  ? __pfx_sock_has_perm+0x10/0x10
[   47.933119]  ? mutex_lock+0x8d/0xe0
[   47.933119]  ? __pfx_mutex_lock+0x10/0x10
[   47.933119]  xfrm_netlink_rcv+0x44/0x50
[   47.933119]  netlink_unicast+0x36f/0x4c0
[   47.933119]  ? __pfx_netlink_unicast+0x10/0x10
[   47.933119]  ? netlink_recvmsg+0x500/0x660
[   47.933119]  netlink_sendmsg+0x3b7/0x700
[   47.933119]  ? __pfx_netlink_sendmsg+0x10/0x10
[   47.933119]  ? update_load_avg+0x591/0xab0
[   47.933119]  ? __pfx_netlink_sendmsg+0x10/0x10
[   47.933119]  sock_sendmsg+0xde/0xe0
[   47.933119]  __sys_sendto+0x18d/0x230
[   47.933119]  ? __pfx___sys_sendto+0x10/0x10
[   47.933119]  ? rb_insert_color+0x1c0/0x280
[   47.933119]  ? timerqueue_add+0x128/0x150
[   47.933119]  ? ktime_get+0x49/0xb0
[   47.933119]  ? __pfx_native_apic_mem_write+0x10/0x10
[   47.933119]  ? lapic_next_event+0x35/0x40
[   47.933119]  ? clockevents_program_event+0xdf/0x140
[   47.933119]  ? hrtimer_interrupt+0x321/0x360
[   47.933119]  __x64_sys_sendto+0x71/0x90
[   47.933119]  do_syscall_64+0x3f/0x90
[   47.933119]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
[   47.933119] RIP: 0033:0x44b8aa
[   47.933119] Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb b9 0f 1f 00 f3 0f 1e fa 41 89 ca 64 8b 04 25 18 00 00 00 85 9
[   47.933119] RSP: 002b:00007fff7ded8258 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
[   47.933119] RAX: ffffffffffffffda RBX: 00007fff7ded9688 RCX: 000000000044b8aa
[   47.933119] RDX: 00000000000002a8 RSI: 00007fff7ded8480 RDI: 0000000000000003
[   47.933119] RBP: 00007fff7ded82c0 R08: 00007fff7ded829c R09: 000000000000000c
[   47.933119] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
[   47.933119] R13: 00007fff7ded9678 R14: 00000000004c37d0 R15: 0000000000000001
[   47.933119]  </TASK>
[   47.933119] Modules linked in:
[   47.933119] CR2: 0000000000000000
[   47.933119] ---[ end trace 0000000000000000 ]---
[   47.933119] RIP: 0010:memcpy_orig+0xad/0x140
[   47.933119] Code: e8 4c 89 5f e0 48 8d 7f e0 73 d2 83 c2 20 48 29 d6 48 29 d7 83 fa 10 72 34 4c 8b 06 4c 8b 4e 08 c
[   47.933119] RSP: 0018:ffff888008f57658 EFLAGS: 00000202
[   47.933119] RAX: 0000000000000000 RBX: ffff888008bd0000 RCX: ffffffff8238e571
[   47.933119] RDX: 0000000000000018 RSI: ffff888007f64844 RDI: 0000000000000000
[   47.933119] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   47.933119] R10: 0000000000000000 R11: 0000000000000000 R12: ffff888008f57818
[   47.933119] R13: ffff888007f64aa4 R14: 0000000000000000 R15: 0000000000000000
[   47.933119] FS:  00000000014013c0(0000) GS:ffff88806d600000(0000) knlGS:0000000000000000
[   47.933119] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   47.933119] CR2: 0000000000000000 CR3: 00000000054d8000 CR4: 00000000000006f0
[   47.933119] Kernel panic - not syncing: Fatal exception in interrupt
[   47.933119] Kernel Offset: disabled
[   47.933119] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

[buggy commit]: 
d8647b79c3b7 ("xfrm: Add user interface for esn and big anti-replay windows")

[root cause]:
x->replay_esn and x->preplay_esn should be allocated at xfrm_alloc_replay_state_esn(...) in xfrm_state_construct(..), 
and then the xfrm_update_ae_params(...) is okay to update them. However, the current implementation allows a malicious 
user to directly dereference the pointer and crash the kernel like above.

[PoC code]:
see attachment poc1.c. I have tested it in ubuntu 22.04 and latest Linux with QEMU.

[suggest fix]:
Add NULL check in xfrm_update_ae_params() like below:

@@ -628,7 +628,7 @@ static void xfrm_update_ae_params(struct xfrm_state *x, struct nlattr **attrs,
        struct nlattr *rt = attrs[XFRMA_REPLAY_THRESH];
        struct nlattr *mt = attrs[XFRMA_MTIMER_THRESH];

-       if (re) {
+       if (re && x->replay_esn && x->preplay_esn) {
                struct xfrm_replay_state_esn *replay_esn;

[fix status]:
to ipsec tree now but not yet upstream, see https://kernel.googlesource.com/pub/scm/linux/kernel/git/klassert/ipsec/

[credit]
Lin Ma from ZJU & Ant Security Light-Year Lab

Attachment: attachment-npd.zip
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