[14/17] crypto: ansi_cprng - If DT is omitted, don't buffer old output

Commit Message

George Spelvin Dec. 2, 2014, 8:58 a.m. UTC

This is a separate patch so it may be considered separately.
I think it's in the spirit of the original ANSI specs, but opinions
are solicited.

Signed-off-by: George Spelvin <[e-mail]>
---
 crypto/ansi_cprng.c | 9 +++++++++
 1 file changed, 9 insertions(+)

I'm really not sure what people will think of this.

Patch

diff --git a/crypto/ansi_cprng.c b/crypto/ansi_cprng.c
index c2c285f3..4ed7c0cf 100644
--- a/crypto/ansi_cprng.c
+++ b/crypto/ansi_cprng.c
@@ -213,6 +213,15 @@  static int get_prng_bytes(unsigned char *buf, unsigned int nbytes,
 	len = nbytes - pos;
 	memcpy(buf + pos, ctx->rand_data.bytes + read_pos, len);
 	read_pos += len;
+	/*
+	 * If not in deterministic mode, never buffer old entropy;
+	 * re-seed on each read request.  This is in the spirit of the
+	 * specifications, which are themselves not clear on the subject
+	 * of multiple requests for output over a period of time.
+	 */
+	if (!(ctx->flags & PRNG_DETERMINISTIC))
+		read_pos = DEFAULT_BLK_SZ;
+
 	memzero_explicit(ctx->rand_data.bytes, read_pos);
 	ctx->rand_read_pos = read_pos;
 	err = nbytes;