Re: [PATCH v2] net/tun: fix ioctl() based info leaks

[Eric Dumazet <eric.dumazet@gmail.com>]

On Mon, 2012-07-30 at 07:45 +0200, Mathias Krause wrote:
> The tun module leaks up to 36 bytes of memory by not fully initializing
> a structure located on the stack that gets copied to user memory by the
> TUNGETIFF and SIOCGIFHWADDR ioctl()s.
> 
> Signed-off-by: Mathias Krause <minipli@googlemail.com>
> ---
> v2:
> - removed braces around else branch
> - minor adjustment of the commit message
> 
>  drivers/net/tun.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 987aeef..01255ff 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1252,9 +1252,11 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
>  	int vnet_hdr_sz;
>  	int ret;
>  
> -	if (cmd == TUNSETIFF || _IOC_TYPE(cmd) == 0x89)
> +	if (cmd == TUNSETIFF || _IOC_TYPE(cmd) == 0x89) {
>  		if (copy_from_user(&ifr, argp, ifreq_len))
>  			return -EFAULT;
> +	} else
> +		memset(&ifr, 0, sizeof(ifr));
>  
>  	if (cmd == TUNGETFEATURES) {
>  		/* Currently this just means: "what IFF flags are valid?".


Actually braces were better

vi +169 Documentation/CodingStyle

This does not apply if only one branch of a conditional statement is a
single
statement; in the latter case use braces in both branches:

if (condition) {
        do_this();
        do_that();
} else {
        otherwise();
}