ACK: [SRU Groovy 2/2] bpf, cgroup: Fix problematic bounds check

[Colin Ian King]

On 18/02/2021 19:39, Thadeu Lima de Souza Cascardo wrote:
> From: Loris Reiff <loris.reiff at liblor.ch>
> 
> Since ctx.optlen is signed, a larger value than max_value could be
> passed, as it is later on used as unsigned, which causes a WARN_ON_ONCE
> in the copy_to_user.
> 
> Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
> Signed-off-by: Loris Reiff <loris.reiff at liblor.ch>
> Signed-off-by: Daniel Borkmann <daniel at iogearbox.net>
> Reviewed-by: Stanislav Fomichev <sdf at google.com>
> Link: https://lore.kernel.org/bpf/20210122164232.61770-2-loris.reiff@liblor.ch
> (cherry picked from commit f4a2da755a7e1f5d845c52aee71336cee289935a)
> CVE-2021-20194
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
> ---
>  kernel/bpf/cgroup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 7bae3686603e..c1fd5ca6fab6 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -1439,7 +1439,7 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
>  		goto out;
>  	}
>  
> -	if (ctx.optlen > max_optlen) {
> +	if (ctx.optlen > max_optlen || ctx.optlen < 0) {
>  		ret = -EFAULT;
>  		goto out;
>  	}
> 
Acked-by: Colin Ian King <colin.king at canonical.com>