netdev - Re: [PATCH] libertas: Avoid reading past end of buffer

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Date:   Wed, 10 May 2017 12:06:02 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        libertas-dev@...ts.infradead.org,
        linux-wireless <linux-wireless@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Micay <danielmicay@...il.com>
Subject: Re: [PATCH] libertas: Avoid reading past end of buffer

On Tue, May 9, 2017 at 9:33 PM, Joe Perches <joe@...ches.com> wrote:
> On Tue, 2017-05-09 at 16:23 -0700, Kees Cook wrote:
>> Using memcpy() from a string that is shorter than the length copied means
>> the destination buffer is being filled with arbitrary data from the kernel
>> rodata segment. Instead, use strncpy() which will fill the trailing bytes
>> with zeros. Additionally adjust indentation to keep checkpatch.pl happy.
>>
>> This was found with the future CONFIG_FORTIFY_SOURCE feature.
> []
>> diff --git a/drivers/net/wireless/marvell/libertas/mesh.c b/drivers/net/wireless/marvell/libertas/mesh.c
> []
>> @@ -1177,9 +1177,9 @@ void lbs_mesh_ethtool_get_strings(struct net_device *dev,
>>       switch (stringset) {
>>       case ETH_SS_STATS:
>>               for (i = 0; i < MESH_STATS_NUM; i++) {
>> -                     memcpy(s + i * ETH_GSTRING_LEN,
>> -                                     mesh_stat_strings[i],
>> -                                     ETH_GSTRING_LEN);
>> +                     strncpy(s + i * ETH_GSTRING_LEN,
>> +                             mesh_stat_strings[i],
>> +                             ETH_GSTRING_LEN);
>>               }
>
> The better solution is to declare
> mesh_stat_strings in in the normal way
>
> ---
>  drivers/net/wireless/marvell/libertas/mesh.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/wireless/marvell/libertas/mesh.c b/drivers/net/wireless/marvell/libertas/mesh.c
> index d0c881dd5846..a535e7f48d2d 100644
> --- a/drivers/net/wireless/marvell/libertas/mesh.c
> +++ b/drivers/net/wireless/marvell/libertas/mesh.c
> @@ -1108,15 +1108,15 @@ void lbs_mesh_set_txpd(struct lbs_private *priv,
>   * Ethtool related
>   */
>
> -static const char * const mesh_stat_strings[] = {
> -                       "drop_duplicate_bcast",
> -                       "drop_ttl_zero",
> -                       "drop_no_fwd_route",
> -                       "drop_no_buffers",
> -                       "fwded_unicast_cnt",
> -                       "fwded_bcast_cnt",
> -                       "drop_blind_table",
> -                       "tx_failed_cnt"
> +static const char mesh_stat_strings[][ETH_GSTRING_LEN] = {
> +       "drop_duplicate_bcast",
> +       "drop_ttl_zero",
> +       "drop_no_fwd_route",
> +       "drop_no_buffers",
> +       "fwded_unicast_cnt",
> +       "fwded_bcast_cnt",
> +       "drop_blind_table",
> +       "tx_failed_cnt",
>  };
>
>  void lbs_mesh_ethtool_get_stats(struct net_device *dev,

Ah yeah! And that simplifies the memcpy too, since it can just do it
in one go. New patch on the way...

-Kees

-- 
Kees Cook
Pixel Security