Re: [PATCH] net/tap: resolve stringop-overflow with gcc 12 on ppc64le

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 22 Mar 2023 17:24:39 -0400
David Christensen <drc@linux.vnet.ibm.com> wrote:

> Building DPDK with gcc 12 on a ppc64le system generates a
> stringop-overflow warning. Replace the local MAC address
> validation function parse_user_mac() with a call to
> rte_ether_unformat_addr() instead.
> 
> Bugzilla ID: 1197
> Cc: stable@dpdk.org
> 
> Signed-off-by: David Christensen <drc@linux.vnet.ibm.com>
> ---
>  drivers/net/tap/rte_eth_tap.c | 25 +------------------------
>  1 file changed, 1 insertion(+), 24 deletions(-)
> 
> diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
> index 089ac202fa..1f83f49c0e 100644
> --- a/drivers/net/tap/rte_eth_tap.c
> +++ b/drivers/net/tap/rte_eth_tap.c
> @@ -2267,29 +2267,6 @@ set_remote_iface(const char *key __rte_unused,
>  	return 0;
>  }
>  
> -static int parse_user_mac(struct rte_ether_addr *user_mac,
> -		const char *value)
> -{
> -	unsigned int index = 0;
> -	char mac_temp[strlen(ETH_TAP_USR_MAC_FMT) + 1], *mac_byte = NULL;
> -
> -	if (user_mac == NULL || value == NULL)
> -		return 0;
> -
> -	strlcpy(mac_temp, value, sizeof(mac_temp));
> -	mac_byte = strtok(mac_temp, ":");
> -
> -	while ((mac_byte != NULL) &&
> -			(strlen(mac_byte) <= 2) &&
> -			(strlen(mac_byte) == strspn(mac_byte,
> -					ETH_TAP_CMP_MAC_FMT))) {
> -		user_mac->addr_bytes[index++] = strtoul(mac_byte, NULL, 16);
> -		mac_byte = strtok(NULL, ":");
> -	}
> -
> -	return index;
> -}
> -
>  static int
>  set_mac_type(const char *key __rte_unused,
>  	     const char *value,
> @@ -2311,7 +2288,7 @@ set_mac_type(const char *key __rte_unused,
>  		goto success;
>  	}
>  
> -	if (parse_user_mac(user_mac, value) != 6)
> +	if (rte_ether_unformat_addr(value, user_mac) < 0)
>  		goto error;
>  success:
>  	TAP_LOG(DEBUG, "TAP user MAC param (%s)", value);

There might still be case where user_mac == NULL since it comes
from extra_args.

Also, this code has this suspicious code:

	if (!strncasecmp(ETH_TAP_MAC_FIXED, value, strlen(ETH_TAP_MAC_FIXED))) {
		static int iface_idx;

		/* fixed mac = 00:64:74:61:70:<iface_idx> */
		memcpy((char *)user_mac->addr_bytes, "\0dtap",
			RTE_ETHER_ADDR_LEN);
		user_mac->addr_bytes[RTE_ETHER_ADDR_LEN - 1] =
			iface_idx++ + '0';
		goto success;
	}

The OUI for that MAC address is not registered but it might be someday.
Choosing magic constants in IANA assigned space is not best practice.
Unless some vendor wants to spend lots of time registering these.

Better to use locally assigned value.  See RFC7042 for more details.