Re: [PATCH] Input: joydev - prevent potential read overflow in ioctl

[Denis Efremov <denis.e.efremov@oracle.com>]

Hi,

CVE-2021-3612 was assigned to this patch.


On 2/17/21 9:10 AM, Dan Carpenter wrote:
> The problem here is that "len" might be less than "joydev->nabs" so the
> loops which verfy abspam[i] and keypam[] might read beyond the buffer.


The added check looks insufficient to me. There are second loops in these
functions with unpatched "i < joydev->nabs;" and "i < joydev->nkey;" checks.

> 
> Fixes: 999b874f4aa3 ("Input: joydev - validate axis/button maps before clobbering current ones")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>  drivers/input/joydev.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/input/joydev.c b/drivers/input/joydev.c
> index a2b5fbba2d3b..750f4513fe20 100644
> --- a/drivers/input/joydev.c
> +++ b/drivers/input/joydev.c
> @@ -456,7 +456,7 @@ static int joydev_handle_JSIOCSAXMAP(struct joydev *joydev,
>  	if (IS_ERR(abspam))
>  		return PTR_ERR(abspam);
>  
> -	for (i = 0; i < joydev->nabs; i++) {
> +	for (i = 0; i < len && i < joydev->nabs; i++) {
>  		if (abspam[i] > ABS_MAX) {
>  			retval = -EINVAL;
>  			goto out;

        memcpy(joydev->abspam, abspam, len);

        for (i = 0; i < joydev->nabs; i++) // <== HERE
                joydev->absmap[joydev->abspam[i]] = i;


> @@ -487,7 +487,7 @@ static int joydev_handle_JSIOCSBTNMAP(struct joydev *joydev,
>  	if (IS_ERR(keypam))
>  		return PTR_ERR(keypam);
>  
> -	for (i = 0; i < joydev->nkey; i++) {
> +	for (i = 0; i < (len / 2) && i < joydev->nkey; i++) {
>  		if (keypam[i] > KEY_MAX || keypam[i] < BTN_MISC) {
>  			retval = -EINVAL;
>  			goto out;
> 

        memcpy(joydev->keypam, keypam, len);

        for (i = 0; i < joydev->nkey; i++) // <== HERE
                joydev->keymap[keypam[i] - BTN_MISC] = i;


Also at the beginning of joydev_handle_JSIOCSAXMAP() there is a
	len = min(len, sizeof(joydev->abspam));
	abspam = memdup_user(argp, len);

Maybe we can call min(len, joydev->nabs) instead or even min3() and
use only len in the for loops then? Same for joydev_handle_JSIOCSBTNMAP.

Thanks,
Denis