netdev - Re: [PATCH iproute2 v2] ipaddress: strengthen check on 'label' input

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Date:   Fri, 1 Jun 2018 15:56:41 -0400
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Patrick Talbert <ptalbert@...hat.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH iproute2 v2] ipaddress: strengthen check on 'label'
 input

On Tue, 29 May 2018 16:57:07 +0200
Patrick Talbert <ptalbert@...hat.com> wrote:

> As mentioned in the ip-address man page, an address label must
> be equal to the device name or prefixed by the device name
> followed by a colon. Currently the only check on this input is
> to see if the device name appears at the beginning of the label
> string.
> 
> This commit adds an additional check to ensure label == dev or
> continues with a colon.
> 
> Signed-off-by: Patrick Talbert <ptalbert@...hat.com>
> Suggested-by: Stephen Hemminger <stephen@...workplumber.org>

Yes, this looks better but still have some feedback.

> ---
>  ip/ipaddress.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/ip/ipaddress.c b/ip/ipaddress.c
> index 00da14c..fce2008 100644
> --- a/ip/ipaddress.c
> +++ b/ip/ipaddress.c
> @@ -2040,6 +2040,22 @@ static bool ipaddr_is_multicast(inet_prefix *a)
>  		return false;
>  }
>  
> +static bool is_valid_label(const char *dev, const char *label)
> +{
> +	char alias[strlen(dev) + 1];
> +
> +	if (strlen(label) < strlen(dev))
> +		return false;
> +
> +	strcpy(alias, dev);
> +	strcat(alias, ":");
> +	if (strncmp(label, dev, strlen(dev)) == 0 ||
> +	    strncmp(label, alias, strlen(alias)) == 0)
> +		return true;
> +	else
> +		return false;
> +}

This string copying and comparison still is much more overhead than it
needs to be. The following tests out to be equivalent with a single strncmp
and strlen.

Why not just:
diff --git a/ip/ipaddress.c b/ip/ipaddress.c
index 00da14c6f97c..eac489e94fe4 100644
--- a/ip/ipaddress.c
+++ b/ip/ipaddress.c
@@ -2040,6 +2040,16 @@ static bool ipaddr_is_multicast(inet_prefix *a)
 		return false;
 }
 
+static bool is_valid_label(const char *label, const char *dev)
+{
+	size_t len = strlen(dev);
+
+	if (strncmp(label, dev, len) != 0)
+		return false;
+
+	return label[len] == '\0' || label[len] == ':';
+}
+
 

Doesn't matter much now, but code seems to get copied.