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

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: ab9f211 ("apparmor: Allow filtering based on secmark policy")
Signed-off-by: Xiao Liang <[email protected]>
Signed-off-by: John Johansen <[email protected]>

Author: leonshaw

security/apparmor/lsm.c

@@ -1304,6 +1304,13 @@ 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);
 }