crypto: ansi_prng - Use just a BH lock

The current code uses a mix of sping_lock() & spin_lock_irqsave(). This can
lead to deadlock with the correct timming & cprng_get_random() + cprng_reset()
sequence.
I've converted them to bottom half locks since all three user grab just a BH
lock so this runs probably in softirq :)
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/ansi_cprng.c

@@ -187,7 +187,6 @@ static int _get_more_prng_bytes(struct prng_context *ctx)
 /* Our exported functions */
 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx)
 {
-	unsigned long flags;
 	unsigned char *ptr = buf;
 	unsigned int byte_count = (unsigned int)nbytes;
 	int err;
@@ -196,7 +195,7 @@ static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx)
 	if (nbytes < 0)
 		return -EINVAL;
 
-	spin_lock_irqsave(&ctx->prng_lock, flags);
+	spin_lock_bh(&ctx->prng_lock);
 
 	err = -EINVAL;
 	if (ctx->flags & PRNG_NEED_RESET)
@@ -268,7 +267,7 @@ empty_rbuf:
 		goto remainder;
 
 done:
-	spin_unlock_irqrestore(&ctx->prng_lock, flags);
+	spin_unlock_bh(&ctx->prng_lock);
 	dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
 		err, ctx);
 	return err;
@@ -287,7 +286,7 @@ static int reset_prng_context(struct prng_context *ctx,
 	int rc = -EINVAL;
 	unsigned char *prng_key;
 
-	spin_lock(&ctx->prng_lock);
+	spin_lock_bh(&ctx->prng_lock);
 	ctx->flags |= PRNG_NEED_RESET;
 
 	prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
@@ -332,7 +331,7 @@ static int reset_prng_context(struct prng_context *ctx,
 	rc = 0;
 	ctx->flags &= ~PRNG_NEED_RESET;
 out:
-	spin_unlock(&ctx->prng_lock);
+	spin_unlock_bh(&ctx->prng_lock);
 
 	return rc;