[PATCH] apparmor: Fix null pointer deref when receiving skb during sock creation

[John Johansen]

On 9/1/23 17:48, Xiao Liang wrote:
> The panic below is observed when receiving ICMP packets with secmark set
> while an ICMP raw socket is being created. SK_CTX(sk)->label is updated
> in apparmor_socket_post_create(), but the packet is delivered to the
> socket before that, causing the null pointer dereference.
> Drop the packet if label context is not set.
> 
>      BUG: kernel NULL pointer dereference, address: 000000000000004c
>      #PF: supervisor read access in kernel mode
>      #PF: error_code(0x0000) - not-present page
>      PGD 0 P4D 0
>      Oops: 0000 [#1] PREEMPT SMP NOPTI
>      CPU: 0 PID: 407 Comm: a.out Not tainted 6.4.12-arch1-1 #1 3e6fa2753a2d75925c34ecb78e22e85a65d083df
>      Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/28/2020
>      RIP: 0010:aa_label_next_confined+0xb/0x40
>      Code: 00 00 48 89 ef e8 d5 25 0c 00 e9 66 ff ff ff 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f 00 0f 1f 44 00 00 89 f0 <8b> 77 4c 39 c6 7e 1f 48 63 d0 48 8d 14 d7 eb 0b 83 c0 01 48 83 c2
>      RSP: 0018:ffffa92940003b08 EFLAGS: 00010246
>      RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000000000000e
>      RDX: ffffa92940003be8 RSI: 0000000000000000 RDI: 0000000000000000
>      RBP: ffff8b57471e7800 R08: ffff8b574c642400 R09: 0000000000000002
>      R10: ffffffffbd820eeb R11: ffffffffbeb7ff00 R12: ffff8b574c642400
>      R13: 0000000000000001 R14: 0000000000000001 R15: 0000000000000000
>      FS:  00007fb092ea7640(0000) GS:ffff8b577bc00000(0000) knlGS:0000000000000000
>      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>      CR2: 000000000000004c CR3: 00000001020f2005 CR4: 00000000007706f0
>      PKRU: 55555554
>      Call Trace:
>       <IRQ>
>       ? __die+0x23/0x70
>       ? page_fault_oops+0x171/0x4e0
>       ? exc_page_fault+0x7f/0x180
>       ? asm_exc_page_fault+0x26/0x30
>       ? aa_label_next_confined+0xb/0x40
>       apparmor_secmark_check+0xec/0x330
>       security_sock_rcv_skb+0x35/0x50
>       sk_filter_trim_cap+0x47/0x250
>       sock_queue_rcv_skb_reason+0x20/0x60
>       raw_rcv+0x13c/0x210
>       raw_local_deliver+0x1f3/0x250
>       ip_protocol_deliver_rcu+0x4f/0x2f0
>       ip_local_deliver_finish+0x76/0xa0
>       __netif_receive_skb_one_core+0x89/0xa0
>       netif_receive_skb+0x119/0x170
>       ? __netdev_alloc_skb+0x3d/0x140
>       vmxnet3_rq_rx_complete+0xb23/0x1010 [vmxnet3 56a84f9c97178c57a43a24ec073b45a9d6f01f3a]
>       vmxnet3_poll_rx_only+0x36/0xb0 [vmxnet3 56a84f9c97178c57a43a24ec073b45a9d6f01f3a]
>       __napi_poll+0x28/0x1b0
>       net_rx_action+0x2a4/0x380
>       __do_softirq+0xd1/0x2c8
>       __irq_exit_rcu+0xbb/0xf0
>       common_interrupt+0x86/0xa0
>       </IRQ>
>       <TASK>
>       asm_common_interrupt+0x26/0x40
>      RIP: 0010:apparmor_socket_post_create+0xb/0x200
>      Code: 08 48 85 ff 75 a1 eb b1 0f 1f 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 41 54 <55> 48 89 fd 53 45 85 c0 0f 84 b2 00 00 00 48 8b 1d 80 56 3f 02 48
>      RSP: 0018:ffffa92940ce7e50 EFLAGS: 00000286
>      RAX: ffffffffbc756440 RBX: 0000000000000000 RCX: 0000000000000001
>      RDX: 0000000000000003 RSI: 0000000000000002 RDI: ffff8b574eaab740
>      RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
>      R10: ffff8b57444cec70 R11: 0000000000000000 R12: 0000000000000003
>      R13: 0000000000000002 R14: ffff8b574eaab740 R15: ffffffffbd8e4748
>       ? __pfx_apparmor_socket_post_create+0x10/0x10
>       security_socket_post_create+0x4b/0x80
>       __sock_create+0x176/0x1f0
>       __sys_socket+0x89/0x100
>       __x64_sys_socket+0x17/0x20
>       do_syscall_64+0x5d/0x90
>       ? do_syscall_64+0x6c/0x90
>       ? do_syscall_64+0x6c/0x90
>       ? do_syscall_64+0x6c/0x90
>       entry_SYSCALL_64_after_hwframe+0x72/0xdc
> 
> Fixes: ab9f2115081a ("apparmor: Allow filtering based on secmark policy")
> Signed-off-by: Xiao Liang <shaw.leon at gmail.com>

not sure how I dropped this one, thanks for the patch. I have pulled it into the apparmor tree

Acked-by: John Johansen <john.johansen at canonical.com>


> ---
>   security/apparmor/lsm.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> index 108eccc5ada5..0dbff677ac2e 100644
> --- a/security/apparmor/lsm.c
> +++ b/security/apparmor/lsm.c
> @@ -1097,6 +1097,13 @@ static int apparmor_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
>   	if (!skb->secmark)
>   		return 0;
>   
> +	/*
> +	 * If reach here before socket_post_create hook is called, in which
> +	 * case label is null, drop the packet.
> +	 */
> +	if (!ctx->label)
> +		return -EACCES;
> +
>   	return apparmor_secmark_check(ctx->label, OP_RECVMSG, AA_MAY_RECEIVE,
>   				      skb->secmark, sk);
>   }