linux-kernel - [PATCHv2 2/2] hwrng: optee: fix wait use case

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Date:   Thu, 23 Jul 2020 10:46:22 +0200
From:   Jorge Ramirez-Ortiz <jorge@...ndries.io>
To:     jorge@...ndries.io, sumit.garg@...aro.org, mpm@...enic.com,
        herbert@...dor.apana.org.au
Cc:     jens.wiklander@...aro.org, arnd@...db.de, ricardo@...ndries.io,
        mike@...ndries.io, gregkh@...uxfoundation.org,
        op-tee@...ts.trustedfirmware.org, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCHv2 2/2] hwrng: optee: fix wait use case

The current code waits for data to be available before attempting a
second read. However the second read would not be executed as the
while loop exits.

This fix does not wait if all data has been read and reads a second
time if only partial data was retrieved on the first read.

This fix also does not attempt to read if not data is requested.

Signed-off-by: Jorge Ramirez-Ortiz <jorge@...ndries.io>
---
 v2: tidy up the while loop to avoid reading when no data is requested

 drivers/char/hw_random/optee-rng.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
index 5bc4700c4dae..a99d82949981 100644
--- a/drivers/char/hw_random/optee-rng.c
+++ b/drivers/char/hw_random/optee-rng.c
@@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
 	if (max > MAX_ENTROPY_REQ_SZ)
 		max = MAX_ENTROPY_REQ_SZ;
 
-	while (read == 0) {
+	while (read < max) {
 		rng_size = get_optee_rng_data(pvt_data, data, (max - read));
 
 		data += rng_size;
 		read += rng_size;
 
 		if (wait && pvt_data->data_rate) {
-			if (timeout-- == 0)
+			if ((timeout-- == 0) || (read == max))
 				return read;
 			msleep((1000 * (max - read)) / pvt_data->data_rate);
 		} else {
-- 
2.17.1