[PATCH 4.14 183/218] tty: synclink_gt: Fix null-pointer-dereference in slgt_clean()

[Greg Kroah-Hartman]

From: Zheyu Ma <zheyuma97@xxxxxxxxx>

[ Upstream commit 689ca31c542687709ba21ec2195c1fbce34fd029 ]

When the driver fails at alloc_hdlcdev(), and then we remove the driver
module, we will get the following splat:

[   25.065966] general protection fault, probably for non-canonical address 0xdffffc0000000182: 0000 [#1] PREEMPT SMP KASAN PTI
[   25.066914] KASAN: null-ptr-deref in range [0x0000000000000c10-0x0000000000000c17]
[   25.069262] RIP: 0010:detach_hdlc_protocol+0x2a/0x3e0
[   25.077709] Call Trace:
[   25.077924]  <TASK>
[   25.078108]  unregister_hdlc_device+0x16/0x30
[   25.078481]  slgt_cleanup+0x157/0x9f0 [synclink_gt]

Fix this by checking whether the 'info->netdev' is a null pointer first.

Reviewed-by: Jiri Slaby <jirislaby@xxxxxxxxxx>
Signed-off-by: Zheyu Ma <zheyuma97@xxxxxxxxx>
Link: https://lore.kernel.org/r/20220410114814.3920474-1-zheyuma97@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/tty/synclink_gt.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/synclink_gt.c b/drivers/tty/synclink_gt.c
index 9d68f89a2bf8..4b5ff6e173bd 100644
--- a/drivers/tty/synclink_gt.c
+++ b/drivers/tty/synclink_gt.c
@@ -1822,6 +1822,8 @@ static int hdlcdev_init(struct slgt_info *info)
  */
 static void hdlcdev_exit(struct slgt_info *info)
 {
+	if (!info->netdev)
+		return;
 	unregister_hdlc_device(info->netdev);
 	free_netdev(info->netdev);
 	info->netdev = NULL;
-- 
2.35.1