netdev - Re: [PATCH net-next] net: qualcomm: rmnet: fix two pointer math bugs

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Date:   Sat, 19 Jun 2021 13:12:09 -0600
From:   subashab@...eaurora.org
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Sean Tranchetti <stranche@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net-next] net: qualcomm: rmnet: fix two pointer math bugs

On 2021-06-19 07:52, Dan Carpenter wrote:
> We recently changed these two pointers from void pointers to struct
> pointers and it breaks the pointer math so now the "txphdr" points
> beyond the end of the buffer.
> 
> Fixes: 56a967c4f7e5 ("net: qualcomm: rmnet: Remove some unneeded 
> casts")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
>  drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index 3ee5c1a8b46e..3676976c875b 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -168,7 +168,7 @@ static void
> rmnet_map_complement_ipv4_txporthdr_csum_field(struct iphdr *ip4h)
>  	void *txphdr;
>  	u16 *csum;
> 
> -	txphdr = ip4h + ip4h->ihl * 4;
> +	txphdr = (void *)ip4h + ip4h->ihl * 4;
> 
>  	if (ip4h->protocol == IPPROTO_TCP || ip4h->protocol == IPPROTO_UDP) {
>  		csum = (u16 *)rmnet_map_get_csum_field(ip4h->protocol, txphdr);
> @@ -203,7 +203,7 @@
> rmnet_map_complement_ipv6_txporthdr_csum_field(struct ipv6hdr *ip6h)
>  	void *txphdr;
>  	u16 *csum;
> 
> -	txphdr = ip6h + sizeof(struct ipv6hdr);
> +	txphdr = ip6h + 1;
> 
>  	if (ip6h->nexthdr == IPPROTO_TCP || ip6h->nexthdr == IPPROTO_UDP) {
>  		csum = (u16 *)rmnet_map_get_csum_field(ip6h->nexthdr, txphdr);

Hi Dan

Thanks for fixing this. Could you cast the ip4h to char* instead of 
void*.
Looks like gcc might raise issues if -Wpointer-arith is used.

https://gcc.gnu.org/onlinedocs/gcc-4.5.0/gcc/Pointer-Arith.html#Pointer-Arith