Subject: Re: [ETH]: Combine format_addr() with print_mac().

From: Joe Perches <[email-masked]>
Date: Fri, 21 Dec 2007 14:36:59 -0800

On Fri, 2007-12-21 at 14:05 -0800, Michael Chan wrote:
> [ETH]: Combine format_addr() with print_mac().
> print_mac() used by most net drivers and format_addr() used by
> net-sysfs.c are very similar and they can be integrated.
> format_addr() is also identically redefined in the qla4xxx iscsi
> driver.
> diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
> index 6b2e454..f760d41 100644
> --- a/net/ethernet/eth.c
> +++ b/net/ethernet/eth.c
> @@ -359,10 +359,33 @@ struct net_device *alloc_etherdev_mq(int sizeof_priv, unsigned int queue_count)
>  }
>  EXPORT_SYMBOL(alloc_etherdev_mq);
>  
> +static ssize_t _format_mac_addr(char *buf, const unsigned char *addr, int len)
> +{
> +	int i;
> +	char *cp = buf;
> +
> +	for (i = 0; i < len; i++) {
> +		cp += sprintf(cp, "%02x", addr[i]);
> +		if (i == len - 1)
> +			break;
> +		*cp++ = ':';
> +	}
> +	return cp - buf;
> +}
> +
> +ssize_t format_mac_addr(char *buf, const unsigned char *addr, int len)
> +{
> +	ssize_t l;
> +
> +	l = _format_mac_addr(buf, addr, len);
> +	strcpy(buf + l, "\n");
> +	return l + 1;
> +}
> +EXPORT_SYMBOL(format_mac_addr);
> +
>  char *print_mac(char *buf, const u8 *addr)
>  {
> -	sprintf(buf, MAC_FMT,
> -		addr[0], addr[1], addr[2], addr[3], addr[4], addr[5]);
> +	_format_mac_addr(buf, addr, ETH_ALEN);
>  	return buf;
>  }
>  EXPORT_SYMBOL(print_mac);

I think const unsigned char *addr should be const u8 *addr
ssize_t? shouldn't it be size_t?
Indexing buf by int len is unchecked.
That could lead to unintended buffer overruns.
Maybe add a buflen argument and use snprintf?

I had a patch that added some type-safety to print_mac
and prevented this unintended buffer overrun.

It seems it wasn't applied.

---------------------------------------

Subject: Re: [PATCH net-2.6.24] introduce MAC_FMT/MAC_ARG
Date: Mon, 24 Sep 2007 10:28:36 -0700

Here is a patch that adds some type safety to print_mac
by using a struct print_mac_buf * instead of char *.

It also reduces the defconfig vmlinux size by 8 bytes.

Signed-off-by:  Joe Perches <[email-masked]>

--

 include/linux/if_ether.h |   12 ++++++++++--
 net/ethernet/eth.c       |    6 +++---
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/include/linux/if_ether.h b/include/linux/if_ether.h
index 57abca1..620d6b1 100644
--- a/include/linux/if_ether.h
+++ b/include/linux/if_ether.h
@@ -126,7 +126,15 @@ extern struct ctl_table ether_table[];
  *     Display a 6 byte device address (MAC) in a readable format.
  */
 #define MAC_FMT "%02x:%02x:%02x:%02x:%02x:%02x"
-extern char *print_mac(char *buf, const u8 *addr);
-#define DECLARE_MAC_BUF(var) char var[18] __maybe_unused
+
+struct print_mac_buf {
+       char formatted_mac_addr[18];
+};
+
+#define DECLARE_MAC_BUF(var) \
+       struct print_mac_buf __maybe_unused _##var; \
+       struct print_mac_buf __maybe_unused *var = &_##var
+
+extern char *print_mac(struct print_mac_buf *buf, const u8 *addr);
 
 #endif /* _LINUX_IF_ETHER_H */
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 2aaf6fa..ad82613 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -338,10 +338,10 @@ struct net_device *alloc_etherdev_mq(int
sizeof_priv, unsigned int queue_count)
 }
 EXPORT_SYMBOL(alloc_etherdev_mq);
 
-char *print_mac(char *buf, const u8 *addr)
+char *print_mac(struct print_mac_buf *buf, const u8 *addr)
 {
-       sprintf(buf, MAC_FMT,
+       sprintf(buf->formatted_mac_addr, MAC_FMT,
                addr[0], addr[1], addr[2], addr[3], addr[4], addr[5]);
-       return buf;
+       return buf->formatted_mac_addr;
 }
 EXPORT_SYMBOL(print_mac);