[PATCH][V2] e1000: avoid null pointer dereference on invalid stat type

[PATCH][V2] e1000: avoid null pointer dereference on invalid stat type

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

Currently if the stat type is invalid then data[i] is being set
either by dereferencing a null pointer p, or it is reading from
an incorrect previous location if we had a valid stat type
previously.  Fix this by nullify pointer p if a stat type is
invalid and only setting data if p is not null.

Detected by CoverityScan, CID#113385 ("Explicit null dereferenced")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/net/ethernet/intel/e1000/e1000_ethtool.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/intel/e1000/e1000_ethtool.c b/drivers/net/ethernet/intel/e1000/e1000_ethtool.c
index ec8aa4562cc9..724c93a6ea92 100644
--- a/drivers/net/ethernet/intel/e1000/e1000_ethtool.c
+++ b/drivers/net/ethernet/intel/e1000/e1000_ethtool.c
@@ -1824,7 +1824,7 @@ static void e1000_get_ethtool_stats(struct net_device *netdev,
 {
 	struct e1000_adapter *adapter = netdev_priv(netdev);
 	int i;
-	char *p = NULL;
+	char *p;
 	const struct e1000_stats *stat = e1000_gstrings_stats;
 
 	e1000_update_stats(adapter);
@@ -1837,16 +1837,18 @@ static void e1000_get_ethtool_stats(struct net_device *netdev,
 			p = (char *)adapter + stat->stat_offset;
 			break;
 		default:
+			p = NULL;
 			WARN_ONCE(1, "Invalid E1000 stat type: %u index %d\n",
 				  stat->type, i);
 			break;
 		}
 
-		if (stat->sizeof_stat == sizeof(u64))
-			data[i] = *(u64 *)p;
-		else
-			data[i] = *(u32 *)p;
-
+		if (p) {
+			if (stat->sizeof_stat == sizeof(u64))
+				data[i] = *(u64 *)p;
+			else
+				data[i] = *(u32 *)p;
+		}
 		stat++;
 	}
 /* BUG_ON(i != E1000_STATS_LEN); */
-- 
2.14.1

Re: [Intel-wired-lan] [PATCH][V2] e1000: avoid null pointer dereference on invalid stat type

[Alexander Duyck]

On Fri, Sep 22, 2017 at 6:41 AM, Colin King <colin.king@canonical.com> wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> Currently if the stat type is invalid then data[i] is being set
> either by dereferencing a null pointer p, or it is reading from
> an incorrect previous location if we had a valid stat type
> previously.  Fix this by nullify pointer p if a stat type is
> invalid and only setting data if p is not null.
>
> Detected by CoverityScan, CID#113385 ("Explicit null dereferenced")
>
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/net/ethernet/intel/e1000/e1000_ethtool.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/e1000/e1000_ethtool.c b/drivers/net/ethernet/intel/e1000/e1000_ethtool.c
> index ec8aa4562cc9..724c93a6ea92 100644
> --- a/drivers/net/ethernet/intel/e1000/e1000_ethtool.c
> +++ b/drivers/net/ethernet/intel/e1000/e1000_ethtool.c
> @@ -1824,7 +1824,7 @@ static void e1000_get_ethtool_stats(struct net_device *netdev,
>  {
>         struct e1000_adapter *adapter = netdev_priv(netdev);
>         int i;
> -       char *p = NULL;
> +       char *p;
>         const struct e1000_stats *stat = e1000_gstrings_stats;
>
>         e1000_update_stats(adapter);

I was honestly happier with the portion of the first patch that moved
this into the loop.

> @@ -1837,16 +1837,18 @@ static void e1000_get_ethtool_stats(struct net_device *netdev,
>                         p = (char *)adapter + stat->stat_offset;
>                         break;
>                 default:
> +                       p = NULL;
>                         WARN_ONCE(1, "Invalid E1000 stat type: %u index %d\n",
>                                   stat->type, i);
>                         break;
>                 }
>
> -               if (stat->sizeof_stat == sizeof(u64))
> -                       data[i] = *(u64 *)p;
> -               else
> -                       data[i] = *(u32 *)p;
> -
> +               if (p) {
> +                       if (stat->sizeof_stat == sizeof(u64))
> +                               data[i] = *(u64 *)p;
> +                       else
> +                               data[i] = *(u32 *)p;
> +               }
>                 stat++;
>         }

Instead of doing all this why not just call out a "continue;" instead
of a "break" if the type isn't recognized, and move the stat++ into
the loop declaration and process it at the same time as i++? That
would clean most of this up and we don't have to worry about any loop
carried variables and the like.

>  /* BUG_ON(i != E1000_STATS_LEN); */
> --
> 2.14.1
>
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