[PATCH 3.16 60/72] appletalk: Fix potential NULL pointer dereference in unregister_snap_client

Ben Hutchings
2019-12-08T13:55:33Z

From: YueHaibing <yuehaibing@huawei.com>

commit 9804501fa1228048857910a6bf23e085aade37cc upstream.

register_snap_client may return NULL, all the callers
check it, but only print a warning. This will result in
NULL pointer dereference in unregister_snap_client and other
places.

It has always been used like this since v2.6

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
include/linux/atalk.h | 2 +-
net/appletalk/aarp.c | 15 ++++++++++++---
net/appletalk/ddp.c | 20 ++++++++++++--------
3 files changed, 25 insertions(+), 12 deletions(-)

--- a/include/linux/atalk.h
+++ b/include/linux/atalk.h
@@ -107,7 +107,7 @@ static __inline__ struct elapaarp *aarp_
#define AARP_RESOLVE_TIME (10 * HZ)

extern struct datalink_proto *ddp_dl, *aarp_dl;
-extern void aarp_proto_init(void);
+extern int aarp_proto_init(void);

/* Inter module exports */

--- a/net/appletalk/aarp.c
+++ b/net/appletalk/aarp.c
@@ -879,15 +879,24 @@ static struct notifier_block aarp_notifi

static unsigned char aarp_snap_id[] = { 0x00, 0x00, 0x00, 0x80, 0xF3 };

-void __init aarp_proto_init(void)
+int __init aarp_proto_init(void)
{
+ int rc;
+
aarp_dl = register_snap_client(aarp_snap_id, aarp_rcv);
- if (!aarp_dl)
+ if (!aarp_dl) {
printk(KERN_CRIT "Unable to register AARP with SNAP.\n");
+ return -ENOMEM;
+ }
setup_timer(&aarp_timer, aarp_expire_timeout, 0);
aarp_timer.expires = jiffies + sysctl_aarp_expiry_time;
add_timer(&aarp_timer);
- register_netdevice_notifier(&aarp_notifier);
+ rc = register_netdevice_notifier(&aarp_notifier);
+ if (rc) {
+ del_timer_sync(&aarp_timer);
+ unregister_snap_client(aarp_dl);
+ }
+ return rc;
}

/* Remove the AARP entries associated with a device. */
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -1912,9 +1912,6 @@ static unsigned char ddp_snap_id[] = { 0
EXPORT_SYMBOL(atrtr_get_dev);
EXPORT_SYMBOL(atalk_find_dev_addr);

-static const char atalk_err_snap[] __initconst =
- KERN_CRIT "Unable to register DDP with SNAP.\n";
-
/* Called by proto.c on kernel start up */
static int __init atalk_init(void)
{
@@ -1929,17 +1926,22 @@ static int __init atalk_init(void)
goto out_proto;

ddp_dl = register_snap_client(ddp_snap_id, atalk_rcv);
- if (!ddp_dl)
- printk(atalk_err_snap);
+ if (!ddp_dl) {
+ pr_crit("Unable to register DDP with SNAP.\n");
+ goto out_sock;
+ }

dev_add_pack(&ltalk_packet_type);
dev_add_pack(&ppptalk_packet_type);

rc = register_netdevice_notifier(&ddp_notifier);
if (rc)
- goto out_sock;
+ goto out_snap;
+
+ rc = aarp_proto_init();
+ if (rc)
+ goto out_dev;

- aarp_proto_init();
rc = atalk_proc_init();
if (rc)
goto out_aarp;
@@ -1953,11 +1955,13 @@ out_proc:
atalk_proc_exit();
out_aarp:
aarp_cleanup_module();
+out_dev:
unregister_netdevice_notifier(&ddp_notifier);
-out_sock:
+out_snap:
dev_remove_pack(&ppptalk_packet_type);
dev_remove_pack(&ltalk_packet_type);
unregister_snap_client(ddp_dl);
+out_sock:
sock_unregister(PF_APPLETALK);
out_proto:
proto_unregister(&ddp_proto);