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From:   YongSu Yoo <yongsuyoo0215@gmail.com>
To:     linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        mchehab@kernel.org, hps@selasky.org,
        kieran.bingham@ideasonboard.com
Cc:     YongSu Yoo <yongsuyoo0215@gmail.com>
Subject: [PATCH] media: dvb_ringbuffer : Fix a bug in dvb_ringbuffer.c
Date:   Thu, 23 Jun 2022 10:35:43 +0000
Message-Id: <20220623103543.4138-1-yongsuyoo0215@gmail.com>
Precedence: bulk

Signed-off-by:Yongsu Yoo <yongsuyoo0215@gmail.com>

The function dvb_ringbuffer_pkt_next in
/linux-next/drviers/media/dvb-core/dvb_ringbuffer.c,
which searches the idx of the next valid packet in the ring
buffer of the ca->slot_info[slot].rx_buffer at
/linux-next/drivers/media/dvb-core/dvb_ca_en50221.c,
has the following problem.
In calculating the amounts of the consumed address of the ring
buffer, if the read address(rbuf->pread) of the ring buffer is
smaller than the idx, the amounts of the searched address
should be (idx - rbuf->pread),
whereas if the read address(rbuf->pread) of the ring buffer is
larger than the idx, the amounts of the consumed address should
be (idx - rbuf->pread + rbug->size). But there exists an
incorrect logic that the rbug-size was not properly added on
(idx - rbug->pread) in the later case. With this commit, we
fixed this bug.
---
 drivers/media/dvb-core/dvb_ringbuffer.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c b/drivers/media/dvb-core/dvb_ringbuffer.c
index d1d471af0636..7d4558de8e83 100644
--- a/drivers/media/dvb-core/dvb_ringbuffer.c
+++ b/drivers/media/dvb-core/dvb_ringbuffer.c
@@ -335,7 +335,9 @@ ssize_t dvb_ringbuffer_pkt_next(struct dvb_ringbuffer *rbuf, size_t idx, size_t*
 		idx = (idx + curpktlen + DVB_RINGBUFFER_PKTHDRSIZE) % rbuf->size;
 	}
 
-	consumed = (idx - rbuf->pread) % rbuf->size;
+	consumed = (idx - rbuf->pread);
+	if (consumed < 0)
+		consumed += rbuf->size;
 
 	while((dvb_ringbuffer_avail(rbuf) - consumed) > DVB_RINGBUFFER_PKTHDRSIZE) {
 
-- 
2.17.1