tipc: fix UAF in error path

Sam Page (sam4k) working with Trend Micro Zero Day Initiative reported
a UAF in the tipc_buf_append() error path:

BUG: KASAN: slab-use-after-free in kfree_skb_list_reason+0x47e/0x4c0
linux/net/core/skbuff.c:1183
Read of size 8 at addr ffff88804d2a7c80 by task poc/8034

CPU: 1 PID: 8034 Comm: poc Not tainted 6.8.2 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.16.0-debian-1.16.0-5 04/01/2014
Call Trace:
 <IRQ>
 __dump_stack linux/lib/dump_stack.c:88
 dump_stack_lvl+0xd9/0x1b0 linux/lib/dump_stack.c:106
 print_address_description linux/mm/kasan/report.c:377
 print_report+0xc4/0x620 linux/mm/kasan/report.c:488
 kasan_report+0xda/0x110 linux/mm/kasan/report.c:601
 kfree_skb_list_reason+0x47e/0x4c0 linux/net/core/skbuff.c:1183
 skb_release_data+0x5af/0x880 linux/net/core/skbuff.c:1026
 skb_release_all linux/net/core/skbuff.c:1094
 __kfree_skb linux/net/core/skbuff.c:1108
 kfree_skb_reason+0x12d/0x210 linux/net/core/skbuff.c:1144
 kfree_skb linux/./include/linux/skbuff.h:1244
 tipc_buf_append+0x425/0xb50 linux/net/tipc/msg.c:186
 tipc_link_input+0x224/0x7c0 linux/net/tipc/link.c:1324
 tipc_link_rcv+0x76e/0x2d70 linux/net/tipc/link.c:1824
 tipc_rcv+0x45f/0x10f0 linux/net/tipc/node.c:2159
 tipc_udp_recv+0x73b/0x8f0 linux/net/tipc/udp_media.c:390
 udp_queue_rcv_one_skb+0xad2/0x1850 linux/net/ipv4/udp.c:2108
 udp_queue_rcv_skb+0x131/0xb00 linux/net/ipv4/udp.c:2186
 udp_unicast_rcv_skb+0x165/0x3b0 linux/net/ipv4/udp.c:2346
 __udp4_lib_rcv+0x2594/0x3400 linux/net/ipv4/udp.c:2422
 ip_protocol_deliver_rcu+0x30c/0x4e0 linux/net/ipv4/ip_input.c:205
 ip_local_deliver_finish+0x2e4/0x520 linux/net/ipv4/ip_input.c:233
 NF_HOOK linux/./include/linux/netfilter.h:314
 NF_HOOK linux/./include/linux/netfilter.h:308
 ip_local_deliver+0x18e/0x1f0 linux/net/ipv4/ip_input.c:254
 dst_input linux/./include/net/dst.h:461
 ip_rcv_finish linux/net/ipv4/ip_input.c:449
 NF_HOOK linux/./include/linux/netfilter.h:314
 NF_HOOK linux/./include/linux/netfilter.h:308
 ip_rcv+0x2c5/0x5d0 linux/net/ipv4/ip_input.c:569
 __netif_receive_skb_one_core+0x199/0x1e0 linux/net/core/dev.c:5534
 __netif_receive_skb+0x1f/0x1c0 linux/net/core/dev.c:5648
 process_backlog+0x101/0x6b0 linux/net/core/dev.c:5976
 __napi_poll.constprop.0+0xba/0x550 linux/net/core/dev.c:6576
 napi_poll linux/net/core/dev.c:6645
 net_rx_action+0x95a/0xe90 linux/net/core/dev.c:6781
 __do_softirq+0x21f/0x8e7 linux/kernel/softirq.c:553
 do_softirq linux/kernel/softirq.c:454
 do_softirq+0xb2/0xf0 linux/kernel/softirq.c:441
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x100/0x120 linux/kernel/softirq.c:381
 local_bh_enable linux/./include/linux/bottom_half.h:33
 rcu_read_unlock_bh linux/./include/linux/rcupdate.h:851
 __dev_queue_xmit+0x871/0x3ee0 linux/net/core/dev.c:4378
 dev_queue_xmit linux/./include/linux/netdevice.h:3169
 neigh_hh_output linux/./include/net/neighbour.h:526
 neigh_output linux/./include/net/neighbour.h:540
 ip_finish_output2+0x169f/0x2550 linux/net/ipv4/ip_output.c:235
 __ip_finish_output linux/net/ipv4/ip_output.c:313
 __ip_finish_output+0x49e/0x950 linux/net/ipv4/ip_output.c:295
 ip_finish_output+0x31/0x310 linux/net/ipv4/ip_output.c:323
 NF_HOOK_COND linux/./include/linux/netfilter.h:303
 ip_output+0x13b/0x2a0 linux/net/ipv4/ip_output.c:433
 dst_output linux/./include/net/dst.h:451
 ip_local_out linux/net/ipv4/ip_output.c:129
 ip_send_skb+0x3e5/0x560 linux/net/ipv4/ip_output.c:1492
 udp_send_skb+0x73f/0x1530 linux/net/ipv4/udp.c:963
 udp_sendmsg+0x1a36/0x2b40 linux/net/ipv4/udp.c:1250
 inet_sendmsg+0x105/0x140 linux/net/ipv4/af_inet.c:850
 sock_sendmsg_nosec linux/net/socket.c:730
 __sock_sendmsg linux/net/socket.c:745
 __sys_sendto+0x42c/0x4e0 linux/net/socket.c:2191
 __do_sys_sendto linux/net/socket.c:2203
 __se_sys_sendto linux/net/socket.c:2199
 __x64_sys_sendto+0xe0/0x1c0 linux/net/socket.c:2199
 do_syscall_x64 linux/arch/x86/entry/common.c:52
 do_syscall_64+0xd8/0x270 linux/arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x6f/0x77 linux/arch/x86/entry/entry_64.S:120
RIP: 0033:0x7f3434974f29
Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
01 f0 ff ff 73 01 c3 48 8b 0d 37 8f 0d 00 f7 d8 64 89 01 48
RSP: 002b:00007fff9154f2b8 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3434974f29
RDX: 00000000000032c8 RSI: 00007fff9154f300 RDI: 0000000000000003
RBP: 00007fff915532e0 R08: 00007fff91553360 R09: 0000000000000010
R10: 0000000000000000 R11: 0000000000000212 R12: 000055ed86d261d0
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

In the critical scenario, either the relevant skb is freed or its
ownership is transferred into a frag_lists. In both cases, the cleanup
code must not free it again: we need to clear the skb reference earlier.

Fixes: 1149557 ("tipc: eliminate unnecessary linearization of incoming buffers")
Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-23852
Acked-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/752f1ccf762223d109845365d07f55414058e5a3.1714484273.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/tipc/msg.c

@@ -156,6 +156,11 @@ int tipc_buf_append(struct sk_buff **headbuf, struct sk_buff **buf)
 	if (!head)
 		goto err;
 
+	/* Either the input skb ownership is transferred to headskb
+	 * or the input skb is freed, clear the reference to avoid
+	 * bad access on error path.
+	 */
+	*buf = NULL;
 	if (skb_try_coalesce(head, frag, &headstolen, &delta)) {
 		kfree_skb_partial(frag, headstolen);
 	} else {
@@ -179,7 +184,6 @@ int tipc_buf_append(struct sk_buff **headbuf, struct sk_buff **buf)
 		*headbuf = NULL;
 		return 1;
 	}
-	*buf = NULL;
 	return 0;
 err:
 	kfree_skb(*buf);