netdev - Re: [PATCH v3] net: don't call strlen on non-terminated string in dev_set

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Message-ID: <20170601134737.7dp2pbnek26b6kqf@yury-thinkpad>
Date:   Thu, 1 Jun 2017 16:47:37 +0300
From:   Yury Norov <ynorov@...iumnetworks.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     dvyukov@...gle.com, kcc@...gle.com, edumazet@...gle.com,
        davem@...emloft.net, stephen@...workplumber.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v3] net: don't call strlen on non-terminated string in
 dev_set_alias()

On Thu, Jun 01, 2017 at 02:38:29PM +0200, Alexander Potapenko wrote:
> KMSAN reported a use of uninitialized memory in dev_set_alias(),
> which was caused by calling strlcpy() (which in turn called strlen())
> on the user-supplied non-terminated string.
> 
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> ---
> v3: removed the multi-line comment
> v2: fixed an off-by-one error spotted by Dmitry Vyukov
 
[...]

> ---
>  net/core/dev.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index fca407b4a6ea..3e3b29133cc9 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1254,7 +1254,9 @@ int dev_set_alias(struct net_device *dev, const char *alias, size_t len)
>  		return -ENOMEM;
>  	dev->ifalias = new_ifalias;
>  
> -	strlcpy(dev->ifalias, alias, len+1);
> +	/* alias comes from the userspace and may not be zero-terminated. */

So if the comment is correct, you'd use copy_from_user() instead.

> +	memcpy(dev->ifalias, alias, len);
> +	dev->ifalias[len] = 0;
>  	return len;
>  }
>  
> -- 
> 2.13.0.219.gdb65acc882-goog