[PATCH v2] mmc: core: Add CIDs for cards to the entropy pool

[Linus Walleij <linus.walleij@linaro.org>]

To make the entropy pool a bit better we can toss in the
CID for eMMC and SD cards into it, usually the serial
number portion is at least unique.

This does not count as improvement of the entropy but
in practice it makes it a bit more random to mix in these
numbers.

Cc: Theodore Ts'o <tytso@mit.edu>
Acked-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v1->v2:
- Move the device_add_randomness() into each mmc_decode_cid()
  function for MMC and SD card.
- Use the raw cid, no reason to unpack the data before using
  it for this purpose.
---
 drivers/mmc/core/mmc.c | 7 +++++++
 drivers/mmc/core/sd.c  | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 6b78ae45c4c9..9804a06ffadd 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/stat.h>
 #include <linux/pm_runtime.h>
+#include <linux/random.h>
 #include <linux/sysfs.h>
 
 #include <linux/mmc/host.h>
@@ -71,6 +72,12 @@ static int mmc_decode_cid(struct mmc_card *card)
 {
 	u32 *resp = card->raw_cid;
 
+	/*
+	 * Add the raw card ID (cid) data to the entropy pool. It doesn't
+	 * matter that not all of it is unique, it's just bonus entropy.
+	 */
+	add_device_randomness(&card->raw_cid, sizeof(card->raw_cid));
+
 	/*
 	 * The selection of the format here is based upon published
 	 * specs from sandisk and from what people have reported.
diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
index 68df6b2f49cc..c5f1df6ce4c0 100644
--- a/drivers/mmc/core/sd.c
+++ b/drivers/mmc/core/sd.c
@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/stat.h>
 #include <linux/pm_runtime.h>
+#include <linux/random.h>
 #include <linux/scatterlist.h>
 #include <linux/sysfs.h>
 
@@ -83,6 +84,12 @@ void mmc_decode_cid(struct mmc_card *card)
 {
 	u32 *resp = card->raw_cid;
 
+	/*
+	 * Add the raw card ID (cid) data to the entropy pool. It doesn't
+	 * matter that not all of it is unique, it's just bonus entropy.
+	 */
+	add_device_randomness(&card->raw_cid, sizeof(card->raw_cid));
+
 	/*
 	 * SD doesn't currently have a version field so we will
 	 * have to assume we can parse this.
-- 
2.35.1