[PATCH] smackfs: restrict bytes count in smackfs write functions

[Casey Schaufler]

On 1/24/2021 6:36 AM, Sabyrzhan Tasbolatov wrote:
> syzbot found WARNINGs in several smackfs write operations where
> bytes count is passed to memdup_user_nul which exceeds
> GFP MAX_ORDER. Check count size if bigger SMK_LONGLABEL,
> for smk_write_syslog if bigger than PAGE_SIZE - 1.
>
> Reported-by: syzbot+a71a442385a0b2815497 at syzkaller.appspotmail.com
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll at gmail.com>

Thank you for the patch. Unfortunately, SMK_LONGLABEL isn't
the right value in some of these cases. 

> ---
>  security/smack/smackfs.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
> index 5d44b7d258ef..88678c6f1b8c 100644
> --- a/security/smack/smackfs.c
> +++ b/security/smack/smackfs.c
> @@ -1167,7 +1167,7 @@ static ssize_t smk_write_net4addr(struct file *file, const char __user *buf,
>  		return -EPERM;
>  	if (*ppos != 0)
>  		return -EINVAL;
> -	if (count < SMK_NETLBLADDRMIN)
> +	if (count < SMK_NETLBLADDRMIN || count > SMK_LONGLABEL)
>  		return -EINVAL;
>  
>  	data = memdup_user_nul(buf, count);
> @@ -1427,7 +1427,7 @@ static ssize_t smk_write_net6addr(struct file *file, const char __user *buf,
>  		return -EPERM;
>  	if (*ppos != 0)
>  		return -EINVAL;
> -	if (count < SMK_NETLBLADDRMIN)
> +	if (count < SMK_NETLBLADDRMIN || count > SMK_LONGLABEL)
>  		return -EINVAL;
>  
>  	data = memdup_user_nul(buf, count);
> @@ -2647,6 +2647,8 @@ static ssize_t smk_write_syslog(struct file *file, const char __user *buf,
>  
>  	if (!smack_privileged(CAP_MAC_ADMIN))
>  		return -EPERM;
> +	if (count > PAGE_SIZE - 1)
> +		return -EINVAL;
>  
>  	data = memdup_user_nul(buf, count);
>  	if (IS_ERR(data))
> @@ -2744,6 +2746,8 @@ static ssize_t smk_write_relabel_self(struct file *file, const char __user *buf,
>  	 */
>  	if (*ppos != 0)
>  		return -EINVAL;
> +	if (count > SMK_LONGLABEL)
> +		return -EINVAL;
>  
>  	data = memdup_user_nul(buf, count);
>  	if (IS_ERR(data))