netdev - Re: [PATCH net] net/bpfilter: initialize pos in __bpfilter_process

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Date:   Thu, 30 Jul 2020 18:13:03 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Christoph Hellwig <hch@....de>
Cc:     davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, netdev@...r.kernel.org, bpf@...r.kernel.org,
        Rodrigo Madera <rodrigo.madera@...il.com>
Subject: Re: [PATCH net] net/bpfilter: initialize pos in
 __bpfilter_process_sockopt

On Thu, Jul 30, 2020 at 06:09:00PM +0200, Christoph Hellwig wrote:
> __bpfilter_process_sockopt never initialized the pos variable passed to
> the pipe write.  This has been mostly harmless in the past as pipes
> ignore the offset, but the switch to kernel_write no verified the

s/no/now/

> position, which can lead to a failure depending on the exact stack
> initialization patter.  Initialize the variable to zero to make

s/patter/pattern/

> rw_verify_area happy.
> 
> Fixes: 6955a76fbcd5 ("bpfilter: switch to kernel_write")
> Reported-by: Christian Brauner <christian.brauner@...ntu.com>
> Reported-by: Rodrigo Madera <rodrigo.madera@...il.com>
> Signed-off-by: Christoph Hellwig <hch@....de>
> Tested-by: Rodrigo Madera <rodrigo.madera@...il.com>
> ---

Thanks for tracking this down, Christoph! This fixes the logging issue
for me.
Tested-by: Christian Brauner <christian.brauner@...ntu.com>
Reviewed-by: Christian Brauner <christian.brauner@...ntu.com>

>  net/bpfilter/bpfilter_kern.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/bpfilter/bpfilter_kern.c b/net/bpfilter/bpfilter_kern.c
> index 1905e01c3aa9a7..4494ea6056cdb8 100644
> --- a/net/bpfilter/bpfilter_kern.c
> +++ b/net/bpfilter/bpfilter_kern.c
> @@ -39,7 +39,7 @@ static int __bpfilter_process_sockopt(struct sock *sk, int optname,
>  {
>  	struct mbox_request req;
>  	struct mbox_reply reply;
> -	loff_t pos;
> +	loff_t pos = 0;
>  	ssize_t n;
>  	int ret = -EFAULT;
>  
> -- 
> 2.27.0
>