Re: [PATCH v2] usb: gadget: configfs: fix OOB read in ext_prop_data_show()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Apr 22, 2026 at 10:39:19AM +0800, Bingquan Chen wrote:
> In ext_prop_data_store(), for unicode property types, the data buffer
> is allocated via kmemdup() with size 'len', but data_len is set to
> len*2+2 to account for the UTF-16 encoding and a 2-byte null
> terminator, as required by the Microsoft OS Extended Properties
> Descriptor specification (dwPropertyDataLength must include the
> terminator).
> 
> However, the null terminator is never actually stored in the data
> buffer. When ext_prop_data_show() reads the data back, it computes the
> read length as data_len >> 1 = len+1, then does memcpy(page, data,
> len+1), reading 1 byte past the allocated buffer. This is a
> slab-out-of-bounds read that leaks 1 byte of adjacent heap data to
> userspace via configfs.
> 
> KASAN report (5.10.252):
> 
>   BUG: KASAN: slab-out-of-bounds in ext_prop_data_show+0x4a/0x60
>   Read of size 9 at addr ffff888005546008 by task poc/62
> 
>   Allocated by task 62:
>    kmemdup+0x17/0x40
>    ext_prop_data_store+0x52/0x130
>    configfs_write_file+0x168/0x200
> 
>   The buggy address belongs to the object at ffff888005546008
>    which belongs to the cache kmalloc-8 of size 8
> 
> Fix by allocating len+2 bytes and explicitly zero-terminating with a
> full 2-byte UTF-16 null terminator. This ensures the buffer fully
> matches the dwPropertyDataLength semantics (len*2+2) while eliminating
> the OOB read.
> 
> Fixes: 7419485f197c ("usb: gadget: configfs: OS Extended Properties descriptors support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Bingquan Chen <patzilla007@gmail.com>
> ---
>  drivers/usb/gadget/configfs.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
> index 183a25f65ac8..b2c3d4e5f6a7 100644
> --- a/drivers/usb/gadget/configfs.c
> +++ b/drivers/usb/gadget/configfs.c
> @@ -1352,8 +1352,12 @@ static ssize_t ext_prop_data_store(struct config_item *item,
> 
>  	if (page[len - 1] == '\n' || page[len - 1] == '\0')
>  		--len;
> -	new_data = kmemdup(page, len, GFP_KERNEL);
> +	new_data = kmalloc(len + 2, GFP_KERNEL);
>  	if (!new_data)
>  		return -ENOMEM;
> +	memcpy(new_data, page, len);
> +	new_data[len]     = '\0';
> +	new_data[len + 1] = '\0';
> 
>  	if (desc->opts_mutex)
> --
> 2.43.0

This patch is corrupted and can not be applied :(