[PATCH v1] usb: typec: altmodes/displayport: fix pin_assignment_show

[PATCH v1] usb: typec: altmodes/displayport: fix pin_assignment_show

[Badhri Jagan Sridharan]

This patch fixes negative indexing of buf array in pin_assignment_show
when get_current_pin_assignments returns 0 i.e. no compatible pin
assignments are found.

BUG: KASAN: use-after-free in pin_assignment_show+0x26c/0x33c
...
Call trace:
dump_backtrace+0x110/0x204
dump_stack_lvl+0x84/0xbc
print_report+0x358/0x974
kasan_report+0x9c/0xfc
__do_kernel_fault+0xd4/0x2d4
do_bad_area+0x48/0x168
do_tag_check_fault+0x24/0x38
do_mem_abort+0x6c/0x14c
el1_abort+0x44/0x68
el1h_64_sync_handler+0x64/0xa4
el1h_64_sync+0x78/0x7c
pin_assignment_show+0x26c/0x33c
dev_attr_show+0x50/0xc0

Fixes: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
Cc: stable@vger.kernel.org
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
---
 drivers/usb/typec/altmodes/displayport.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
index 8f3e884222ad..66de880b28d0 100644
--- a/drivers/usb/typec/altmodes/displayport.c
+++ b/drivers/usb/typec/altmodes/displayport.c
@@ -516,6 +516,10 @@ static ssize_t pin_assignment_show(struct device *dev,
 
 	mutex_unlock(&dp->lock);
 
+	/* get_current_pin_assignments can return 0 when no matching pin assignments are found */
+	if (len == 0)
+		len++;
+
 	buf[len - 1] = '\n';
 	return len;
 }

base-commit: ac9a78681b921877518763ba0e89202254349d1b
-- 
2.40.1.521.gf1e218fcd8-goog

Re: [PATCH v1] usb: typec: altmodes/displayport: fix pin_assignment_show

[Heikki Krogerus]

On Mon, May 08, 2023 at 09:44:43PM +0000, Badhri Jagan Sridharan wrote:
> This patch fixes negative indexing of buf array in pin_assignment_show
> when get_current_pin_assignments returns 0 i.e. no compatible pin
> assignments are found.
> 
> BUG: KASAN: use-after-free in pin_assignment_show+0x26c/0x33c
> ...
> Call trace:
> dump_backtrace+0x110/0x204
> dump_stack_lvl+0x84/0xbc
> print_report+0x358/0x974
> kasan_report+0x9c/0xfc
> __do_kernel_fault+0xd4/0x2d4
> do_bad_area+0x48/0x168
> do_tag_check_fault+0x24/0x38
> do_mem_abort+0x6c/0x14c
> el1_abort+0x44/0x68
> el1h_64_sync_handler+0x64/0xa4
> el1h_64_sync+0x78/0x7c
> pin_assignment_show+0x26c/0x33c
> dev_attr_show+0x50/0xc0
> 
> Fixes: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
> Cc: stable@vger.kernel.org
> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>

Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>

> ---
>  drivers/usb/typec/altmodes/displayport.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
> index 8f3e884222ad..66de880b28d0 100644
> --- a/drivers/usb/typec/altmodes/displayport.c
> +++ b/drivers/usb/typec/altmodes/displayport.c
> @@ -516,6 +516,10 @@ static ssize_t pin_assignment_show(struct device *dev,
>  
>  	mutex_unlock(&dp->lock);
>  
> +	/* get_current_pin_assignments can return 0 when no matching pin assignments are found */
> +	if (len == 0)
> +		len++;
> +
>  	buf[len - 1] = '\n';
>  	return len;
>  }

thanks,

-- 
heikki