From eed9496a0501357aa326ddd6b71408189ed872eb Mon Sep 17 00:00:00 2001
From: Dan Carpenter <error27@gmail.com>
Date: Tue, 7 Mar 2023 11:00:23 +0100
Subject: [PATCH] media: av7110: prevent underflow in write_ts_to_decoder()
Git-commit: eed9496a0501357aa326ddd6b71408189ed872eb
Patch-mainline: v6.4-rc1
References: git-fixes

The buf[4] value comes from the user via ts_play().  It is a value in
the u8 range.  The final length we pass to av7110_ipack_instant_repack()
is "len - (buf[4] + 1) - 4" so add a check to ensure that the length is
not negative.  It's not clear that passing a negative len value does
anything bad necessarily, but it's not best practice.

With the new bounds checking the "if (!len)" condition is no longer
possible or required so remove that.

Fixes: fd46d16d602a ("V4L/DVB (11759): dvb-ttpci: Add TS replay capability")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/staging/media/av7110/av7110_av.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/media/av7110/av7110_av.c b/drivers/staging/media/av7110/av7110_av.c
index 0bf513c26b6b..a5c5bebad306 100644
--- a/drivers/staging/media/av7110/av7110_av.c
+++ b/drivers/staging/media/av7110/av7110_av.c
@@ -823,10 +823,10 @@ static int write_ts_to_decoder(struct av7110 *av7110, int type, const u8 *buf, s
 		av7110_ipack_flush(ipack);
 
 	if (buf[3] & ADAPT_FIELD) {
+		if (buf[4] > len - 1 - 4)
+			return 0;
 		len -= buf[4] + 1;
 		buf += buf[4] + 1;
-		if (!len)
-			return 0;
 	}
 
 	av7110_ipack_instant_repack(buf + 4, len - 4, ipack);
-- 
2.35.3