[v2] RANDOM: ATH9K RNG delivers zero bits of entropy

Commit Message

Stephan Mueller Aug. 7, 2016, 9:36 a.m. UTC

The ATH9K driver implements an RNG which is completely bypassing the
standard Linux HW generator logic.

The RNG may or may not deliver entropy. Considering the conservative
approach in treating entropy with respect to non-auditable sources, this
patch changes the delivered entropy value to zero. The RNG still feeds
data into the input_pool but it is assumed to have no entropy.

When the ATH9K RNG changes to use the HW RNG framework, it may re-enable
the entropy estimation considering that a user can change that value at
boot and runtime.

Reviewed-by: Jason Cooper <[e-mail]>
Signed-off-by: Stephan Mueller <[e-mail]>
---
 drivers/net/wireless/ath/ath9k/rng.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

Comments

Kalle Valo Sept. 27, 2016, 2:44 p.m. UTC | #1

Stephan Mueller <[e-mail]> wrote:
> The ATH9K driver implements an RNG which is completely bypassing the
> standard Linux HW generator logic.
> 
> The RNG may or may not deliver entropy. Considering the conservative
> approach in treating entropy with respect to non-auditable sources, this
> patch changes the delivered entropy value to zero. The RNG still feeds
> data into the input_pool but it is assumed to have no entropy.
> 
> When the ATH9K RNG changes to use the HW RNG framework, it may re-enable
> the entropy estimation considering that a user can change that value at
> boot and runtime.
> 
> Reviewed-by: Jason Cooper <[e-mail]>
> Signed-off-by: Stephan Mueller <[e-mail]>

Based on the discussion I'm dropping this patch. But the discussion was
hard to follow so please let me know if I misunderstood.

Patch set to Rejected.

Stephan Mueller Sept. 27, 2016, 3:17 p.m. UTC | #2

Am Dienstag, 27. September 2016, 16:44:16 CEST schrieb Kalle Valo:

Hi Kalle,

> Stephan Mueller <[e-mail]> wrote:
> > The ATH9K driver implements an RNG which is completely bypassing the
> > standard Linux HW generator logic.
> > 
> > The RNG may or may not deliver entropy. Considering the conservative
> > approach in treating entropy with respect to non-auditable sources, this
> > patch changes the delivered entropy value to zero. The RNG still feeds
> > data into the input_pool but it is assumed to have no entropy.
> > 
> > When the ATH9K RNG changes to use the HW RNG framework, it may re-enable
> > the entropy estimation considering that a user can change that value at
> > boot and runtime.
> > 
> > Reviewed-by: Jason Cooper <[e-mail]>
> > Signed-off-by: Stephan Mueller <[e-mail]>
> 
> Based on the discussion I'm dropping this patch. But the discussion was
> hard to follow so please let me know if I misunderstood.

I guess the rejection is appropriate, but something needs to be done: 
add_hwgenerator_randomness should not be used in this scenario.
> 
> Patch set to Rejected.



Ciao
Stephan
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Patch

diff --git a/drivers/net/wireless/ath/ath9k/rng.c b/drivers/net/wireless/ath/ath9k/rng.c
index d38e50f..1ed8338 100644
--- a/drivers/net/wireless/ath/ath9k/rng.c
+++ b/drivers/net/wireless/ath/ath9k/rng.c
@@ -22,7 +22,6 @@ 
 #include "ar9003_phy.h"
 
 #define ATH9K_RNG_BUF_SIZE	320
-#define ATH9K_RNG_ENTROPY(x)	(((x) * 8 * 320) >> 10) /* quality: 320/1024 */
 
 static int ath9k_rng_data_read(struct ath_softc *sc, u32 *buf, u32 buf_size)
 {
@@ -92,8 +91,7 @@  static int ath9k_rng_kthread(void *data)
 		fail_stats = 0;
 
 		/* sleep until entropy bits under write_wakeup_threshold */
-		add_hwgenerator_randomness((void *)rng_buf, bytes_read,
-					   ATH9K_RNG_ENTROPY(bytes_read));
+		add_hwgenerator_randomness((void *)rng_buf, bytes_read, 0);
 	}
 
 	kfree(rng_buf);