2020-10-29 08:55:11

by Macpaul Lin

Subject: [PATCH v2] usb: gadget: configfs: Fix use-after-free issue with udc_name

From: Eddie Hung <[email protected]>

There is a use-after-free issue, if access udc_name
in function gadget_dev_desc_UDC_store after another context
free udc_name in function unregister_gadget.

Context 1:
gadget_dev_desc_UDC_store()->unregister_gadget()->
free udc_name->set udc_name to NULL

Context 2:
gadget_dev_desc_UDC_show()-> access udc_name

Call trace:
dump_backtrace+0x0/0x340
show_stack+0x14/0x1c
dump_stack+0xe4/0x134
print_address_description+0x78/0x478
__kasan_report+0x270/0x2ec
kasan_report+0x10/0x18
__asan_report_load1_noabort+0x18/0x20
string+0xf4/0x138
vsnprintf+0x428/0x14d0
sprintf+0xe4/0x12c
gadget_dev_desc_UDC_show+0x54/0x64
configfs_read_file+0x210/0x3a0
__vfs_read+0xf0/0x49c
vfs_read+0x130/0x2b4
SyS_read+0x114/0x208
el0_svc_naked+0x34/0x38

Add mutex_lock to protect this kind of scenario.

Signed-off-by: Eddie Hung <[email protected]>
Signed-off-by: Macpaul Lin <[email protected]>
Reviewed-by: Peter Chen <[email protected]>
Cc: [email protected]
---
Changes for v2:
- Fix typo %s/contex/context, Thanks Peter.

drivers/usb/gadget/configfs.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index 56051bb..d9743f4 100644
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c
@@ -221,9 +221,16 @@ static ssize_t gadget_dev_desc_bcdUSB_store(struct config_item *item,

static ssize_t gadget_dev_desc_UDC_show(struct config_item *item, char *page)
{
- char *udc_name = to_gadget_info(item)->composite.gadget_driver.udc_name;
+ struct gadget_info *gi = to_gadget_info(item);
+ char *udc_name;
+ int ret;
+
+ mutex_lock(&gi->lock);
+ udc_name = gi->composite.gadget_driver.udc_name;
+ ret = sprintf(page, "%s\n", udc_name ?: "");
+ mutex_unlock(&gi->lock);

- return sprintf(page, "%s\n", udc_name ?: "");
+ return ret;
}

static int unregister_gadget(struct gadget_info *gi)
--
1.7.9.5

2020-10-29 08:57:35

by Macpaul Lin

Subject: Re: [PATCH v2] usb: gadget: configfs: Fix use-after-free issue with udc_name

On Thu, 2020-10-29 at 01:55 +0800, Macpaul Lin wrote:
> From: Eddie Hung <[email protected]>
>
> There is a use-after-free issue, if access udc_name
> in function gadget_dev_desc_UDC_store after another context
> free udc_name in function unregister_gadget.
>
> Context 1:
> gadget_dev_desc_UDC_store()->unregister_gadget()->
> free udc_name->set udc_name to NULL
>
> Context 2:
> gadget_dev_desc_UDC_show()-> access udc_name
>
> Call trace:
> dump_backtrace+0x0/0x340
> show_stack+0x14/0x1c
> dump_stack+0xe4/0x134
> print_address_description+0x78/0x478
> __kasan_report+0x270/0x2ec
> kasan_report+0x10/0x18
> __asan_report_load1_noabort+0x18/0x20
> string+0xf4/0x138
> vsnprintf+0x428/0x14d0
> sprintf+0xe4/0x12c
> gadget_dev_desc_UDC_show+0x54/0x64
> configfs_read_file+0x210/0x3a0
> __vfs_read+0xf0/0x49c
> vfs_read+0x130/0x2b4
> SyS_read+0x114/0x208
> el0_svc_naked+0x34/0x38
>
> Add mutex_lock to protect this kind of scenario.
>
> Signed-off-by: Eddie Hung <[email protected]>
> Signed-off-by: Macpaul Lin <[email protected]>
> Reviewed-by: Peter Chen <[email protected]>
> Cc: [email protected]
> ---
> Changes for v2:
> - Fix typo %s/contex/context, Thanks Peter.
>
> drivers/usb/gadget/configfs.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
> index 56051bb..d9743f4 100644
> --- a/drivers/usb/gadget/configfs.c
> +++ b/drivers/usb/gadget/configfs.c
> @@ -221,9 +221,16 @@ static ssize_t gadget_dev_desc_bcdUSB_store(struct config_item *item,
>
> static ssize_t gadget_dev_desc_UDC_show(struct config_item *item, char *page)
> {
> - char *udc_name = to_gadget_info(item)->composite.gadget_driver.udc_name;
> + struct gadget_info *gi = to_gadget_info(item);
> + char *udc_name;
> + int ret;
> +
> + mutex_lock(&gi->lock);
> + udc_name = gi->composite.gadget_driver.udc_name;
> + ret = sprintf(page, "%s\n", udc_name ?: "");
> + mutex_unlock(&gi->lock);
>
> - return sprintf(page, "%s\n", udc_name ?: "");
> + return ret;
> }
>
> static int unregister_gadget(struct gadget_info *gi)

Sorry, it looks like still a base64 encoded mail.
I'll feedback to our IT department again.
Please ignore this mail.

Thanks
Macpaul Lin