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

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(-)

From: Mathias Krause <minipli@googlemail.com>
Date: Mon, 30 Jul 2012 07:45:14 +0200

> 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>

Applied and queued up for -stable, thanks.
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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();
}


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From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 30 Jul 2012 08:22:20 +0200

> 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();
> }

Ok I'll fix this up myself.
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