[PATCH] ethtool: Use kcalloc instead of kmalloc for ethtool_get_strings

[Joe Perches <joe@perches.com>]

It seems that kernel memory can leak into userspace by a
kmalloc, ethtool_get_strings, then copy_to_user sequence.

Avoid this by using kcalloc to zero fill the copied buffer.

Signed-off-by: Joe Perches <joe@perches.com>
---

stable too...

On Tue, 2015-10-13 at 23:59 -0700, Jeff Kirsher wrote:
> From: Jacob Keller <jacob.e.keller@intel.com>
[]
> diff --git a/drivers/net/ethernet/intel/fm10k/fm10k_ethtool.c b/drivers/net/ethernet/intel/fm10k/fm10k_ethtool.c
[]
> @@ -206,13 +206,13 @@ static void fm10k_get_stat_strings(struct net_device *dev, u8 *data)
>  	}
>  
>  	for (i = 0; i < interface->hw.mac.max_queues; i++) {
> -		sprintf(p, "tx_queue_%u_packets", i);
> +		snprintf(p, ETH_GSTRING_LEN, "tx_queue_%u_packets", i);

It seems these need a memset after the snprintf to zero fill
bytes after the string terminating \0 to avoid leaking
contents of any unset bytes.

It'd probably be better to allocate a zeroed buffer instead.

>  		p += ETH_GSTRING_LEN;
> -		sprintf(p, "tx_queue_%u_bytes", i);
> +		snprintf(p, ETH_GSTRING_LEN, "tx_queue_%u_bytes", i);

so...

 net/core/ethtool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index b495ab1..29edf74 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -1284,7 +1284,7 @@ static int ethtool_get_strings(struct net_device *dev, void __user *useraddr)
 
 	gstrings.len = ret;
 
-	data = kmalloc(gstrings.len * ETH_GSTRING_LEN, GFP_USER);
+	data = kcalloc(gstrings.len, ETH_GSTRING_LEN, GFP_USER);
 	if (!data)
 		return -ENOMEM;