netdev - Re: [iproute PATCH v2 7/7] lib/ll_map: Make sure im->name is NULL-terminated

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Message-ID: <20170818093328.4d3eff55@xeon-e3>
Date:   Fri, 18 Aug 2017 09:33:28 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Phil Sutter <phil@....cc>
Cc:     netdev@...r.kernel.org
Subject: Re: [iproute PATCH v2 7/7] lib/ll_map: Make sure im->name is
 NULL-terminated

On Thu, 17 Aug 2017 19:09:32 +0200
Phil Sutter <phil@....cc> wrote:

> Signed-off-by: Phil Sutter <phil@....cc>
> ---
>  lib/ll_map.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/ll_map.c b/lib/ll_map.c
> index 4e4556c9ac80b..4d06eb69f138a 100644
> --- a/lib/ll_map.c
> +++ b/lib/ll_map.c
> @@ -120,11 +120,11 @@ int ll_remember_index(const struct sockaddr_nl *who,
>  		return 0;
>  	}
>  
> -	im = malloc(sizeof(*im));
> +	im = calloc(1, sizeof(*im));
>  	if (im == NULL)
>  		return 0;
>  	im->index = ifi->ifi_index;
> -	strcpy(im->name, ifname);
> +	strncpy(im->name, ifname, IFNAMSIZ - 1);
>  	im->type = ifi->ifi_type;
>  	im->flags = ifi->ifi_flags;
>  

This is not really necessary. kernel won't return
an ifname with a length >= IFNAMSIZ.

If you wanted to future proof it, why not use variable size allocation

--- a/lib/ll_map.c
+++ b/lib/ll_map.c
@@ -30,7 +30,7 @@ struct ll_cache {
        unsigned        flags;
        unsigned        index;
        unsigned short  type;
-       char            name[IFNAMSIZ];
+       char            name[];
 };
 
 #define IDXMAP_SIZE    1024
@@ -120,7 +120,7 @@ int ll_remember_index(const struct sockaddr_nl *who,
                return 0;
        }
 
-       im = malloc(sizeof(*im));
+       im = malloc(sizeof(*im) + strlen(ifname) + 1);
        if (im == NULL)
                return 0;
        im->index = ifi->ifi_index;