net/tun: fix ioctl() based info leaks

The tun module leaks up to 36 bytes of memory by not 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>
---
 drivers/net/tun.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

On Sun, Jul 29, 2012 at 10:58 PM, Mathias Krause <minipli@googlemail.com> wrote:
> The tun module leaks up to 36 bytes of memory by not 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>
> ---
>  drivers/net/tun.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 987aeef..cadeb94 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1252,9 +1252,12 @@ 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?".

The fix makes sense to me.

Beside of the fix, why are you adding braces to if and else?
We don't use braces on single statements.

On Mon, Jul 30, 2012 at 1:11 AM, richard -rw- weinberger
<richard.weinberger@gmail.com> wrote:
> On Sun, Jul 29, 2012 at 10:58 PM, Mathias Krause <minipli@googlemail.com> wrote:
>> -       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?".
>
> The fix makes sense to me.
>
> Beside of the fix, why are you adding braces to if and else?

The pair of braces around the "if" is needed to attach the "else"
branch to the right "if". The braces around the "else" are just for
consistency.

> We don't use braces on single statements.

Even tun.c isn't consistently following this rule but I'll send a new
patch without the "else" braces.


Thanks,
Mathias
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