[PATCH] libertas: Avoid reading past end of buffer

[PATCH] libertas: Avoid reading past end of buffer

[Kees Cook]

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.

Cc: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/net/wireless/marvell/libertas/mesh.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/marvell/libertas/mesh.c b/drivers/net/wireless/marvell/libertas/mesh.c
index d0c881dd5846..d0b1948ca242 100644
--- 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);
 		}
 		break;
 	}
-- 
2.7.4


-- 
Kees Cook
Pixel Security

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

[Joe Perches]

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,

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

[Kees Cook]

On Tue, May 9, 2017 at 9:33 PM, Joe Perches <joe@perches.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

[PATCH] libertas: Avoid reading past end of buffer

[Kees Cook]

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, redefine the stat strings to be ETH_GSTRING_LEN
sizes, like other drivers. This lets us use a single memcpy that does not
leak rodata contents. Additionally adjust indentation to keep checkpatch.pl
happy.

This was found with the future CONFIG_FORTIFY_SOURCE feature.

Cc: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
v2: use ETH_GSTRING_LEN; joe
---
 drivers/net/wireless/marvell/libertas/mesh.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/drivers/net/wireless/marvell/libertas/mesh.c b/drivers/net/wireless/marvell/libertas/mesh.c
index d0c881dd5846..6076c83ce5ab 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[MESH_STATS_NUM][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,
@@ -1170,17 +1170,11 @@ int lbs_mesh_ethtool_get_sset_count(struct net_device *dev, int sset)
 void lbs_mesh_ethtool_get_strings(struct net_device *dev,
 	uint32_t stringset, uint8_t *s)
 {
-	int i;
-
 	lbs_deb_enter(LBS_DEB_ETHTOOL);
 
 	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);
-		}
+		memcpy(s, *mesh_stat_strings, sizeof(mesh_stat_strings));
 		break;
 	}
 	lbs_deb_enter(LBS_DEB_ETHTOOL);
-- 
2.7.4


-- 
Kees Cook
Pixel Security

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

[Joe Perches]

On Wed, 2017-05-10 at 12:24 -0700, Kees Cook wrote:
> Using memcpy() from a string that is shorter than the length copied means
[]
> diff --git a/drivers/net/wireless/marvell/libertas/mesh.c b/drivers/net/wireless/marvell/libertas/mesh.c
[]
> @@ -1170,17 +1170,11 @@ int lbs_mesh_ethtool_get_sset_count(struct net_device *dev, int sset)
>  void lbs_mesh_ethtool_get_strings(struct net_device *dev,
>  	uint32_t stringset, uint8_t *s)
>  {
> -	int i;
> -
>  	lbs_deb_enter(LBS_DEB_ETHTOOL);
>  
>  	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);
> -		}
> +		memcpy(s, *mesh_stat_strings, sizeof(mesh_stat_strings));
>  		break;
>  	}
>  	lbs_deb_enter(LBS_DEB_ETHTOOL);

unrelated trivia:

lbs_deb_enter is used incorrectly here at
function exit as both enter and leave calls.

That type of copy/paste defect may be common.

$ git grep -w lbs_deb_enter | wc -l
148
$ git grep -w lbs_deb_leave | wc -l
71

One would expect these numbers to be the same.

Another option would be to delete all these
calls as ftrace function tracing works well.

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

[Joe Perches]

On Wed, 2017-05-10 at 12:24 -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. 

another bit of trivia:

> diff --git a/drivers/net/wireless/marvell/libertas/mesh.c b/drivers/net/wireless/marvell/libertas/mesh.c
[]
> @@ -1170,17 +1170,11 @@ int lbs_mesh_ethtool_get_sset_count(struct net_device *dev, int sset)
[]
> +		memcpy(s, *mesh_stat_strings, sizeof(mesh_stat_strings));

That * isn't necessary.

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

[Kalle Valo]

Joe Perches <joe@perches.com> writes:

> unrelated trivia:
>
> lbs_deb_enter is used incorrectly here at
> function exit as both enter and leave calls.
>
> That type of copy/paste defect may be common.
>
> $ git grep -w lbs_deb_enter | wc -l
> 148
> $ git grep -w lbs_deb_leave | wc -l
> 71
>
> One would expect these numbers to be the same.
>
> Another option would be to delete all these
> calls as ftrace function tracing works well.

Yeah, deleting all the enter/exit calls would be better.

-- 
Kalle Valo