[PATCH net] net: hsr: Fix null-ptr-deref in hsr_proxy_announce

[Edward Adam Davis <eadavis@qq.com>]

The NULL pointer is interlink, return by hsr_port_get_hsr(), before using it,
it is necessary to add a null pointer check.

[Syzbot reported]
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
CPU: 0 UID: 0 PID: 11 Comm: kworker/u8:0 Not tainted 6.11.0-rc6-syzkaller-00180-g4c8002277167 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
Workqueue: netns cleanup_net
RIP: 0010:send_hsr_supervision_frame+0x37/0xa90 net/hsr/hsr_device.c:290
Code: 53 48 83 ec 38 48 89 54 24 30 49 89 f7 49 89 fd 48 bb 00 00 00 00 00 fc ff df e8 54 a0 f9 f5 49 8d 6d 18 48 89 e8 48 c1 e8 03 <80> 3c 18 00 74 08 48 89 ef e8 7b e6 60 f6 48 8b 6d 00 4d 89 fc 49
RSP: 0018:ffffc90000007a70 EFLAGS: 00010206
RAX: 0000000000000003 RBX: dffffc0000000000 RCX: ffff88801ced3c00
RDX: 0000000000000100 RSI: ffffc90000007b40 RDI: 0000000000000000
RBP: 0000000000000018 R08: ffffffff8b995013 R09: 1ffffffff283c908
R10: dffffc0000000000 R11: ffffffff8b99ec30 R12: ffff888065030e98
R13: 0000000000000000 R14: ffff888065030cf0 R15: ffffc90000007b40
FS:  0000000000000000(0000) GS:ffff8880b8800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f76c4f21cf8 CR3: 000000000e734000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 hsr_proxy_announce+0x23a/0x4c0 net/hsr/hsr_device.c:420
 call_timer_fn+0x18e/0x650 kernel/time/timer.c:1792
 expire_timers kernel/time/timer.c:1843 [inline]
 __run_timers kernel/time/timer.c:2417 [inline]
 __run_timer_base+0x66a/0x8e0 kernel/time/timer.c:2428
 run_timer_base kernel/time/timer.c:2437 [inline]
 run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2447
 handle_softirqs+0x2c4/0x970 kernel/softirq.c:554
 __do_softirq kernel/softirq.c:588 [inline]
 invoke_softirq kernel/softirq.c:428 [inline]
 __irq_exit_rcu+0xf4/0x1c0 kernel/softirq.c:637
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:649
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1043
 
Fixes: 5f703ce5c98 ("net: hsr: Send supervisory frames to HSR network with ProxyNodeTable data")
Reported-by: syzbot+c229849f5b6c82eba3c2@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 net/hsr/hsr_device.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/hsr/hsr_device.c b/net/hsr/hsr_device.c
index ac56784c327..c4a06ee6fb9 100644
--- a/net/hsr/hsr_device.c
+++ b/net/hsr/hsr_device.c
@@ -414,6 +414,9 @@ static void hsr_proxy_announce(struct timer_list *t)
 	 * of SAN nodes stored in ProxyNodeTable.
 	 */
 	interlink = hsr_port_get_hsr(hsr, HSR_PT_INTERLINK);
+	if (!interlink)
+		goto out;
+
 	list_for_each_entry_rcu(node, &hsr->proxy_node_db, mac_list) {
 		if (hsr_addr_is_redbox(hsr, node->macaddress_A))
 			continue;
@@ -428,6 +431,7 @@ static void hsr_proxy_announce(struct timer_list *t)
 		mod_timer(&hsr->announce_proxy_timer, jiffies + interval);
 	}
 
+out:	
 	rcu_read_unlock();
 }
 
-- 
2.43.0