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

[Thadeu Lima de Souza Cascardo]

On Tue, Mar 02, 2021 at 11:32:08AM -0700, Tim Gardner wrote:
> From: Loris Reiff <loris.reiff at liblor.ch>
> 
> CVE-2021-20194
> 
> 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)
> Signed-off-by: Tim Gardner <tim.gardner at canonical.com>

Acked-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>

Clean cherry-pick.

Thanks.
Cascardo.

> ---
>  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 117a283d278e..e376eef9f107 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -1124,7 +1124,7 @@ 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;
>  	}
> -- 
> 2.17.1
> 
> 
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