[PATCH] net.c: Don't forget about the first fragment.

[Sascha Hauer]

On Tue, Jul 04, 2023 at 07:55:35PM +0200, Christian Melki wrote:
> It's possible to request very large messages using
> the current code base. F.ex. UDP datagrams with the tftp client.
> The tftp servers will happily reply with fragmented IP frames.
> All these frame parts need to be dropped as BB currently doesn't
> do fragment reassembly.
> 
> The current check was for fragment offsets only (0x1fff).
> But the first frame has fragment offset 0 and would slip through
> this check. That could result in a seemingly OK frame
> for the tftp client, but with broken data.
> 
> Add check for the MF (More Fragments) flag. Should cover the
> first packet too.
> 
> Signed-off-by: Christian Melki <christian.melki at t2data.com>
> ---
>  net/net.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/net/net.c b/net/net.c
> index 19161d2e82..b842041d59 100644
> --- a/net/net.c
> +++ b/net/net.c
> @@ -678,7 +678,12 @@ static int net_handle_ip(struct eth_device *edev, unsigned char *pkt, int len)
>  	if ((ip->hl_v & 0xf0) != 0x40)
>  		goto bad;
>  
> -	if (ip->frag_off & htons(0x1fff)) /* Can't deal w/ fragments */
> +	/* Can't deal w/ fragments.
> +	 * Ether a fragment offset (13 bits), or
> +	 * MF (More Fragments) from frag. flags (3 bits).
> +	 * MF - because first fragment has fragment offset 0
> +	 */
> +	if (ip->frag_off & htons(0x3fff)) 

Nice catch ;)

Applied with typo fixed (Ether->Either)

Sascha

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |