random: fix error in entropy extraction

Fix cast error in entropy extraction.
Add comments explaining the magic 16.
Remove extra confusing loop variable.

Signed-off-by: Matt Mackall <mpm@selenic.com>
Acked-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 5 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 46c1b97748b6..9705b439448a 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -760,7 +760,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
 
 static void extract_buf(struct entropy_store *r, __u8 *out)
 {
-        int i, x;
+        int i;
         __u32 data[16], buf[5 + SHA_WORKSPACE_WORDS];
 
         sha_init(buf);
@@ -772,9 +772,11 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
          * attempts to find previous ouputs), unless the hash
          * function can be inverted.
          */
-        for (i = 0, x = 0; i < r->poolinfo->poolwords; i += 16, x+=2) {
-                sha_transform(buf, (__u8 *)r->pool+i, buf + 5);
-                add_entropy_words(r, &buf[x % 5], 1);
+        for (i = 0; i < r->poolinfo->poolwords; i += 16) {
+                /* hash blocks of 16 words = 512 bits */
+                sha_transform(buf, (__u8 *)(r->pool + i), buf + 5);
+                /* feed back portion of the resulting hash */
+                add_entropy_words(r, &buf[i % 5], 1);
         }
 
         /*
@@ -782,7 +784,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
          * portion of the pool while mixing, and hash one
          * final time.
          */
-        __add_entropy_words(r, &buf[x % 5], 1, data);
+        __add_entropy_words(r, &buf[i % 5], 1, data);
         sha_transform(buf, (__u8 *)data, buf + 5);
 
         /*