[PATCH] net: check for dev pointer being NULL in dev_hard_header() to avoid GPF

[George Kennedy]

The dev pointer can be NULL in dev_hard_header(). Add check for dev being
NULL in dev_hard_header() to avoid GPF.

general protection fault, probably for non-canonical address
    0xdffffc0000000046: 0000 [#1] PREEMPT SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000230-0x0000000000000237]
CPU: 1 PID: 45 Comm: kworker/1:1 Not tainted 6.1.0-rc7+ #2
Hardware name: Red Hat KVM, BIOS 1.15.0-2.module+el8.6.0+20659+3dcf7c70
Workqueue: mld mld_ifc_work
RIP: 0010:macvlan_hard_header (./include/linux/netdevice.h:3057
    (discriminator 4) drivers/net/macvlan.c:594 (discriminator 4))
RSP: 0018:ffff888103d377d0 EFLAGS: 00010212
RAX: dffffc0000000000 RBX: ffff88801cf1a000 RCX: 0000000000000000
RDX: 0000000000000046 RSI: 0000000000000000 RDI: 0000000000000230
RBP: ffff88801e8ef328 R08: 0000000000000000 R09: 0000000000000060
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88801f0497c0
R13: 0000000000000000 R14: ffff888045187c98 R15: 0000000000000060
FS:  0000000000000000(0000) GS:ffff888106c80000(0000)
    knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbf3f1c1840 CR3: 0000000014e36000 CR4: 00000000000006e0
Call Trace:
 <TASK>
neigh_connected_output (./include/linux/netdevice.h:3060
    net/core/neighbour.c:1595)
ip6_finish_output2 (./include/net/neighbour.h:546
    net/ipv6/ip6_output.c:134)
ip6_finish_output (net/ipv6/ip6_output.c:195 net/ipv6/ip6_output.c:206)
ip6_output (./include/linux/netfilter.h:291 net/ipv6/ip6_output.c:227)
NF_HOOK.constprop.0 (./include/net/dst.h:445
    ./include/linux/netfilter.h:302)
mld_sendpack (net/ipv6/mcast.c:1824)
mld_send_cr (net/ipv6/mcast.c:2122)
mld_ifc_work (net/ipv6/mcast.c:2655)
process_one_work (kernel/workqueue.c:2294)
worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2437)
kthread (kernel/kthread.c:376)
ret_from_fork (arch/x86/entry/entry_64.S:312)
 </TASK>
Modules linked in:
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace 0000000000000000 ]---

Fixes: 0c4e85813d0a ("[NET]: Wrap netdevice hardware header creation.")
Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx>
---
 include/linux/netdevice.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index eddf8ee270e7..9b25a6301fa5 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3054,7 +3054,7 @@ static inline int dev_hard_header(struct sk_buff *skb, struct net_device *dev,
 				  const void *daddr, const void *saddr,
 				  unsigned int len)
 {
-	if (!dev->header_ops || !dev->header_ops->create)
+	if (!dev || !dev->header_ops || !dev->header_ops->create)
 		return 0;
 
 	return dev->header_ops->create(skb, dev, type, daddr, saddr, len);
-- 
2.31.1