[PATCH] tty: synclink_gt: Fix null-pointer-dereference in slgt_clean()

[PATCH] tty: synclink_gt: Fix null-pointer-dereference in slgt_clean()

[Zheyu Ma]

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.

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 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 25c558e65ece..9bc2a9265277 100644
--- a/drivers/tty/synclink_gt.c
+++ b/drivers/tty/synclink_gt.c
@@ -1746,6 +1746,8 @@ 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;
-- 
2.25.1

Re: [PATCH] tty: synclink_gt: Fix null-pointer-dereference in slgt_clean()

[Jiri Slaby]

On 10. 04. 22, 13:48, Zheyu Ma wrote:
> 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.

Hi,

LGTM

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>

Out of curiosity, do you use the driver, or you only do some static 
analysis?

> Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
> ---
>   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 25c558e65ece..9bc2a9265277 100644
> --- a/drivers/tty/synclink_gt.c
> +++ b/drivers/tty/synclink_gt.c
> @@ -1746,6 +1746,8 @@ 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;


-- 
js
suse labs

Re: [PATCH] tty: synclink_gt: Fix null-pointer-dereference in slgt_clean()

[Zheyu Ma]

On Mon, Apr 11, 2022 at 6:13 PM Jiri Slaby <jirislaby@kernel.org> wrote:
>
> On 10. 04. 22, 13:48, Zheyu Ma wrote:
> > 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.
>
> Hi,
>
> LGTM
>
> Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
>
> Out of curiosity, do you use the driver, or you only do some static
> analysis?

In fact, neither. I test the driver via fuzzing in a simulated environment.

Zheyu Ma